yt-dlp/yt_dlp/postprocessor/ffmpeg.py

from __future__ import unicode_literals

import io
import itertools
import os
import subprocess
import time
import re
import json

from .common import AudioConversionError, PostProcessor

from ..compat import compat_str
from ..utils import (
    dfxp2srt,
    encodeArgument,
    encodeFilename,
    float_or_none,
    _get_exe_version_output,
    detect_exe_version,
    is_outdated_version,
    ISO639Utils,
    orderedSet,
    Popen,
    PostProcessingError,
    prepend_extension,
    replace_extension,
    shell_quote,
    traverse_obj,
    variadic,
)


EXT_TO_OUT_FORMATS = {
    'aac': 'adts',
    'flac': 'flac',
    'm4a': 'ipod',
    'mka': 'matroska',
    'mkv': 'matroska',
    'mpg': 'mpeg',
    'ogv': 'ogg',
    'ts': 'mpegts',
    'wma': 'asf',
    'wmv': 'asf',
    'vtt': 'webvtt',
}
ACODECS = {
    'mp3': 'libmp3lame',
    'aac': 'aac',
    'flac': 'flac',
    'm4a': 'aac',
    'opus': 'libopus',
    'vorbis': 'libvorbis',
    'wav': None,
}


class FFmpegPostProcessorError(PostProcessingError):
    pass


class FFmpegPostProcessor(PostProcessor):
    def __init__(self, downloader=None):
        PostProcessor.__init__(self, downloader)
        self._determine_executables()

    def check_version(self):
        if not self.available:
            raise FFmpegPostProcessorError('ffmpeg not found. Please install or provide the path using --ffmpeg-location')

        required_version = '10-0' if self.basename == 'avconv' else '1.0'
        if is_outdated_version(
                self._versions[self.basename], required_version):
            warning = 'Your copy of %s is outdated, update %s to version %s or newer if you encounter any errors.' % (
                self.basename, self.basename, required_version)
            self.report_warning(warning)

    @staticmethod
    def get_versions_and_features(downloader=None):
        pp = FFmpegPostProcessor(downloader)
        return pp._versions, pp._features

    @staticmethod
    def get_versions(downloader=None):
        return FFmpegPostProcessor.get_version_and_features(downloader)[0]

    def _determine_executables(self):
        programs = ['avprobe', 'avconv', 'ffmpeg', 'ffprobe']

        def get_ffmpeg_version(path, prog):
            out = _get_exe_version_output(path, ['-bsfs'])
            ver = detect_exe_version(out) if out else False
            if ver:
                regexs = [
                    r'(?:\d+:)?([0-9.]+)-[0-9]+ubuntu[0-9.]+$',  # Ubuntu, see [1]
                    r'n([0-9.]+)$',  # Arch Linux
                    # 1. http://www.ducea.com/2006/06/17/ubuntu-package-version-naming-explanation/
                ]
                for regex in regexs:
                    mobj = re.match(regex, ver)
                    if mobj:
                        ver = mobj.group(1)
            self._versions[prog] = ver
            if prog != 'ffmpeg' or not out:
                return

            mobj = re.search(r'(?m)^\s+libavformat\s+(?:[0-9. ]+)\s+/\s+(?P<runtime>[0-9. ]+)', out)
            lavf_runtime_version = mobj.group('runtime').replace(' ', '') if mobj else None
            self._features = {
                'fdk': '--enable-libfdk-aac' in out,
                'setts': 'setts' in out.splitlines(),
                'needs_adtstoasc': is_outdated_version(lavf_runtime_version, '57.56.100', False),
            }

        self.basename = None
        self.probe_basename = None
        self._paths = None
        self._versions = None
        self._features = {}

        prefer_ffmpeg = self.get_param('prefer_ffmpeg', True)
        location = self.get_param('ffmpeg_location')
        if location is None:
            self._paths = {p: p for p in programs}
        else:
            if not os.path.exists(location):
                self.report_warning(
                    'ffmpeg-location %s does not exist! '
                    'Continuing without ffmpeg.' % (location))
                self._versions = {}
                return
            elif os.path.isdir(location):
                dirname, basename = location, None
            else:
                basename = os.path.splitext(os.path.basename(location))[0]
                basename = next((p for p in programs if basename.startswith(p)), 'ffmpeg')
                dirname = os.path.dirname(os.path.abspath(location))
                if basename in ('ffmpeg', 'ffprobe'):
                    prefer_ffmpeg = True

            self._paths = dict(
                (p, os.path.join(dirname, p)) for p in programs)
            if basename:
                self._paths[basename] = location

        self._versions = {}
        for p in programs:
            get_ffmpeg_version(self._paths[p], p)

        if prefer_ffmpeg is False:
            prefs = ('avconv', 'ffmpeg')
        else:
            prefs = ('ffmpeg', 'avconv')
        for p in prefs:
            if self._versions[p]:
                self.basename = p
                break

        if prefer_ffmpeg is False:
            prefs = ('avprobe', 'ffprobe')
        else:
            prefs = ('ffprobe', 'avprobe')
        for p in prefs:
            if self._versions[p]:
                self.probe_basename = p
                break

    @property
    def available(self):
        return self.basename is not None

    @property
    def executable(self):
        return self._paths[self.basename]

    @property
    def probe_available(self):
        return self.probe_basename is not None

    @property
    def probe_executable(self):
        return self._paths[self.probe_basename]

    def get_audio_codec(self, path):
        if not self.probe_available and not self.available:
            raise PostProcessingError('ffprobe and ffmpeg not found. Please install or provide the path using --ffmpeg-location')
        try:
            if self.probe_available:
                cmd = [
                    encodeFilename(self.probe_executable, True),
                    encodeArgument('-show_streams')]
            else:
                cmd = [
                    encodeFilename(self.executable, True),
                    encodeArgument('-i')]
            cmd.append(encodeFilename(self._ffmpeg_filename_argument(path), True))
            self.write_debug('%s command line: %s' % (self.basename, shell_quote(cmd)))
            handle = Popen(cmd, stdin=subprocess.PIPE, stdout=subprocess.PIPE, stderr=subprocess.PIPE)
            stdout_data, stderr_data = handle.communicate_or_kill()
            expected_ret = 0 if self.probe_available else 1
            if handle.wait() != expected_ret:
                return None
        except (IOError, OSError):
            return None
        output = (stdout_data if self.probe_available else stderr_data).decode('ascii', 'ignore')
        if self.probe_available:
            audio_codec = None
            for line in output.split('\n'):
                if line.startswith('codec_name='):
                    audio_codec = line.split('=')[1].strip()
                elif line.strip() == 'codec_type=audio' and audio_codec is not None:
                    return audio_codec
        else:
            # Stream #FILE_INDEX:STREAM_INDEX[STREAM_ID](LANGUAGE): CODEC_TYPE: CODEC_NAME
            mobj = re.search(
                r'Stream\s*#\d+:\d+(?:\[0x[0-9a-f]+\])?(?:\([a-z]{3}\))?:\s*Audio:\s*([0-9a-z]+)',
                output)
            if mobj:
                return mobj.group(1)
        return None

    def get_metadata_object(self, path, opts=[]):
        if self.probe_basename != 'ffprobe':
            if self.probe_available:
                self.report_warning('Only ffprobe is supported for metadata extraction')
            raise PostProcessingError('ffprobe not found. Please install or provide the path using --ffmpeg-location')
        self.check_version()

        cmd = [
            encodeFilename(self.probe_executable, True),
            encodeArgument('-hide_banner'),
            encodeArgument('-show_format'),
            encodeArgument('-show_streams'),
            encodeArgument('-print_format'),
            encodeArgument('json'),
        ]

        cmd += opts
        cmd.append(encodeFilename(self._ffmpeg_filename_argument(path), True))
        self.write_debug('ffprobe command line: %s' % shell_quote(cmd))
        p = Popen(cmd, stdout=subprocess.PIPE, stderr=subprocess.PIPE, stdin=subprocess.PIPE)
        stdout, stderr = p.communicate()
        return json.loads(stdout.decode('utf-8', 'replace'))

    def get_stream_number(self, path, keys, value):
        streams = self.get_metadata_object(path)['streams']
        num = next(
            (i for i, stream in enumerate(streams) if traverse_obj(stream, keys, casesense=False) == value),
            None)
        return num, len(streams)

    def _get_real_video_duration(self, info, fatal=True):
        try:
            if '_real_duration' not in info:
                info['_real_duration'] = float_or_none(
                    traverse_obj(self.get_metadata_object(info['filepath']), ('format', 'duration')))
            if not info['_real_duration']:
                raise PostProcessingError('ffprobe returned empty duration')
        except PostProcessingError as e:
            if fatal:
                raise PostProcessingError(f'Unable to determine video duration; {e}')
        return info.setdefault('_real_duration', None)

    def _duration_mismatch(self, d1, d2):
        if not d1 or not d2:
            return None
        return abs(d1 - d2) > 1

    def run_ffmpeg_multiple_files(self, input_paths, out_path, opts, **kwargs):
        return self.real_run_ffmpeg(
            [(path, []) for path in input_paths],
            [(out_path, opts)], **kwargs)

    def real_run_ffmpeg(self, input_path_opts, output_path_opts, *, expected_retcodes=(0,)):
        self.check_version()

        oldest_mtime = min(
            os.stat(encodeFilename(path)).st_mtime for path, _ in input_path_opts if path)

        cmd = [encodeFilename(self.executable, True), encodeArgument('-y')]
        # avconv does not have repeat option
        if self.basename == 'ffmpeg':
            cmd += [encodeArgument('-loglevel'), encodeArgument('repeat+info')]

        def make_args(file, args, name, number):
            keys = ['_%s%d' % (name, number), '_%s' % name]
            if name == 'o' and number == 1:
                keys.append('')
            args += self._configuration_args(self.basename, keys)
            if name == 'i':
                args.append('-i')
            return (
                [encodeArgument(arg) for arg in args]
                + [encodeFilename(self._ffmpeg_filename_argument(file), True)])

        for arg_type, path_opts in (('i', input_path_opts), ('o', output_path_opts)):
            cmd += itertools.chain.from_iterable(
                make_args(path, list(opts), arg_type, i + 1)
                for i, (path, opts) in enumerate(path_opts) if path)

        self.write_debug('ffmpeg command line: %s' % shell_quote(cmd))
        p = Popen(cmd, stdout=subprocess.PIPE, stderr=subprocess.PIPE, stdin=subprocess.PIPE)
        stdout, stderr = p.communicate_or_kill()
        if p.returncode not in variadic(expected_retcodes):
            stderr = stderr.decode('utf-8', 'replace').strip()
            self.write_debug(stderr)
            raise FFmpegPostProcessorError(stderr.split('\n')[-1])
        for out_path, _ in output_path_opts:
            if out_path:
                self.try_utime(out_path, oldest_mtime, oldest_mtime)
        return stderr.decode('utf-8', 'replace')

    def run_ffmpeg(self, path, out_path, opts, **kwargs):
        return self.run_ffmpeg_multiple_files([path], out_path, opts, **kwargs)

    @staticmethod
    def _ffmpeg_filename_argument(fn):
        # Always use 'file:' because the filename may contain ':' (ffmpeg
        # interprets that as a protocol) or can start with '-' (-- is broken in
        # ffmpeg, see https://ffmpeg.org/trac/ffmpeg/ticket/2127 for details)
        # Also leave '-' intact in order not to break streaming to stdout.
        if fn.startswith(('http://', 'https://')):
            return fn
        return 'file:' + fn if fn != '-' else fn

    @staticmethod
    def _quote_for_ffmpeg(string):
        # See https://ffmpeg.org/ffmpeg-utils.html#toc-Quoting-and-escaping
        # A sequence of '' produces '\'''\'';
        # final replace removes the empty '' between \' \'.
        string = string.replace("'", r"'\''").replace("'''", "'")
        # Handle potential ' at string boundaries.
        string = string[1:] if string[0] == "'" else "'" + string
        return string[:-1] if string[-1] == "'" else string + "'"

    def force_keyframes(self, filename, timestamps):
        timestamps = orderedSet(timestamps)
        if timestamps[0] == 0:
            timestamps = timestamps[1:]
        keyframe_file = prepend_extension(filename, 'keyframes.temp')
        self.to_screen(f'Re-encoding "{filename}" with appropriate keyframes')
        self.run_ffmpeg(filename, keyframe_file, ['-force_key_frames', ','.join(
            f'{t:.6f}' for t in timestamps)])
        return keyframe_file

    def concat_files(self, in_files, out_file, concat_opts=None):
        """
        Use concat demuxer to concatenate multiple files having identical streams.

        Only inpoint, outpoint, and duration concat options are supported.
        See https://ffmpeg.org/ffmpeg-formats.html#concat-1 for details
        """
        concat_file = f'{out_file}.concat'
        self.write_debug(f'Writing concat spec to {concat_file}')
        with open(concat_file, 'wt', encoding='utf-8') as f:
            f.writelines(self._concat_spec(in_files, concat_opts))

        out_flags = ['-c', 'copy']
        if out_file.rpartition('.')[-1] in ('mp4', 'mov'):
            # For some reason, '-c copy' is not enough to copy subtitles
            out_flags.extend(['-c:s', 'mov_text', '-movflags', '+faststart'])

        try:
            self.real_run_ffmpeg(
                [(concat_file, ['-hide_banner', '-nostdin', '-f', 'concat', '-safe', '0'])],
                [(out_file, out_flags)])
        finally:
            os.remove(concat_file)

    @classmethod
    def _concat_spec(cls, in_files, concat_opts=None):
        if concat_opts is None:
            concat_opts = [{}] * len(in_files)
        yield 'ffconcat version 1.0\n'
        for file, opts in zip(in_files, concat_opts):
            yield f'file {cls._quote_for_ffmpeg(cls._ffmpeg_filename_argument(file))}\n'
            # Iterate explicitly to yield the following directives in order, ignoring the rest.
            for directive in 'inpoint', 'outpoint', 'duration':
                if directive in opts:
                    yield f'{directive} {opts[directive]}\n'


class FFmpegExtractAudioPP(FFmpegPostProcessor):
    COMMON_AUDIO_EXTS = ('wav', 'flac', 'm4a', 'aiff', 'mp3', 'ogg', 'mka', 'opus', 'wma')
    SUPPORTED_EXTS = ('best', 'aac', 'flac', 'mp3', 'm4a', 'opus', 'vorbis', 'wav')

    def __init__(self, downloader=None, preferredcodec=None, preferredquality=None, nopostoverwrites=False):
        FFmpegPostProcessor.__init__(self, downloader)
        self._preferredcodec = preferredcodec or 'best'
        self._preferredquality = float_or_none(preferredquality)
        self._nopostoverwrites = nopostoverwrites

    def _quality_args(self, codec):
        if self._preferredquality is None:
            return []
        elif self._preferredquality > 10:
            return ['-b:a', f'{self._preferredquality}k']

        limits = {
            'libmp3lame': (10, 0),
            # FFmpeg's AAC encoder does not have an upper limit for the value of -q:a.
            # Experimentally, with values over 4, bitrate changes were minimal or non-existent
            'aac': (0.1, 4),
            'vorbis': (0, 10),
            'libfdk_aac': (1, 5),
            'opus': None,  # doesn't support -q:a
            'wav': None,
            'flac': None,
        }[codec]
        if not limits:
            return []

        q = limits[1] + (limits[0] - limits[1]) * (self._preferredquality / 10)
        if codec == 'libfdk_aac':
            return ['-vbr', f'{int(q)}']
        return ['-q:a', f'{q}']

    def run_ffmpeg(self, path, out_path, codec, more_opts):
        if codec is None:
            acodec_opts = []
        else:
            acodec_opts = ['-acodec', codec]
        opts = ['-vn'] + acodec_opts + more_opts
        try:
            FFmpegPostProcessor.run_ffmpeg(self, path, out_path, opts)
        except FFmpegPostProcessorError as err:
            raise AudioConversionError(err.msg)

    @PostProcessor._restrict_to(images=False)
    def run(self, information):
        path = information['filepath']
        orig_ext = information['ext']

        if self._preferredcodec == 'best' and orig_ext in self.COMMON_AUDIO_EXTS:
            self.to_screen('Skipping audio extraction since the file is already in a common audio format')
            return [], information

        filecodec = self.get_audio_codec(path)
        if filecodec is None:
            raise PostProcessingError('WARNING: unable to obtain file audio codec with ffprobe')

        more_opts = []
        if self._preferredcodec == 'best' or self._preferredcodec == filecodec or (self._preferredcodec == 'm4a' and filecodec == 'aac'):
            if filecodec == 'aac' and self._preferredcodec in ['m4a', 'best']:
                # Lossless, but in another container
                acodec = 'copy'
                extension = 'm4a'
                more_opts = ['-bsf:a', 'aac_adtstoasc']
            elif filecodec in ['aac', 'flac', 'mp3', 'vorbis', 'opus']:
                # Lossless if possible
                acodec = 'copy'
                extension = filecodec
                if filecodec == 'aac':
                    more_opts = ['-f', 'adts']
                if filecodec == 'vorbis':
                    extension = 'ogg'
            else:
                # MP3 otherwise.
                acodec = 'libmp3lame'
                extension = 'mp3'
                more_opts = self._quality_args(acodec)
        else:
            # We convert the audio (lossy if codec is lossy)
            acodec = ACODECS[self._preferredcodec]
            if acodec == 'aac' and self._features.get('fdk'):
                acodec = 'libfdk_aac'
            extension = self._preferredcodec
            more_opts = self._quality_args(acodec)
            if self._preferredcodec == 'aac':
                more_opts += ['-f', 'adts']
            if self._preferredcodec == 'm4a':
                more_opts += ['-bsf:a', 'aac_adtstoasc']
            if self._preferredcodec == 'vorbis':
                extension = 'ogg'
            if self._preferredcodec == 'wav':
                extension = 'wav'
                more_opts += ['-f', 'wav']

        prefix, sep, ext = path.rpartition('.')  # not os.path.splitext, since the latter does not work on unicode in all setups
        new_path = prefix + sep + extension

        information['filepath'] = new_path
        information['ext'] = extension

        # If we download foo.mp3 and convert it to... foo.mp3, then don't delete foo.mp3, silly.
        if (new_path == path
                or (self._nopostoverwrites and os.path.exists(encodeFilename(new_path)))):
            self.to_screen('Post-process file %s exists, skipping' % new_path)
            return [], information

        try:
            self.to_screen('Destination: ' + new_path)
            self.run_ffmpeg(path, new_path, acodec, more_opts)
        except AudioConversionError as e:
            raise PostProcessingError(
                'audio conversion failed: ' + e.msg)
        except Exception:
            raise PostProcessingError('error running ' + self.basename)

        # Try to update the date time for extracted audio file.
        if information.get('filetime') is not None:
            self.try_utime(
                new_path, time.time(), information['filetime'],
                errnote='Cannot update utime of audio file')

        return [path], information


class FFmpegVideoConvertorPP(FFmpegPostProcessor):
    SUPPORTED_EXTS = ('mp4', 'mkv', 'flv', 'webm', 'mov', 'avi', 'mp3', 'mka', 'm4a', 'ogg', 'opus')
    FORMAT_RE = re.compile(r'{0}(?:/{0})*$'.format(r'(?:\w+>)?(?:%s)' % '|'.join(SUPPORTED_EXTS)))
    _ACTION = 'converting'

    def __init__(self, downloader=None, preferedformat=None):
        super(FFmpegVideoConvertorPP, self).__init__(downloader)
        self._preferedformats = preferedformat.lower().split('/')

    def _target_ext(self, source_ext):
        for pair in self._preferedformats:
            kv = pair.split('>')
            if len(kv) == 1 or kv[0].strip() == source_ext:
                return kv[-1].strip()

    @staticmethod
    def _options(target_ext):
        if target_ext == 'avi':
            return ['-c:v', 'libxvid', '-vtag', 'XVID']
        return []

    @PostProcessor._restrict_to(images=False)
    def run(self, info):
        filename, source_ext = info['filepath'], info['ext'].lower()
        target_ext = self._target_ext(source_ext)
        _skip_msg = (
            f'could not find a mapping for {source_ext}' if not target_ext
            else f'already is in target format {source_ext}' if source_ext == target_ext
            else None)
        if _skip_msg:
            self.to_screen(f'Not {self._ACTION} media file {filename!r}; {_skip_msg}')
            return [], info

        outpath = replace_extension(filename, target_ext, source_ext)
        self.to_screen(f'{self._ACTION.title()} video from {source_ext} to {target_ext}; Destination: {outpath}')
        self.run_ffmpeg(filename, outpath, self._options(target_ext))

        info['filepath'] = outpath
        info['format'] = info['ext'] = target_ext
        return [filename], info


class FFmpegVideoRemuxerPP(FFmpegVideoConvertorPP):
    _ACTION = 'remuxing'

    @staticmethod
    def _options(target_ext):
        options = ['-c', 'copy', '-map', '0', '-dn']
        if target_ext in ['mp4', 'm4a', 'mov']:
            options.extend(['-movflags', '+faststart'])
        return options


class FFmpegEmbedSubtitlePP(FFmpegPostProcessor):
    def __init__(self, downloader=None, already_have_subtitle=False):
        super(FFmpegEmbedSubtitlePP, self).__init__(downloader)
        self._already_have_subtitle = already_have_subtitle

    @PostProcessor._restrict_to(images=False)
    def run(self, information):
        if information['ext'] not in ('mp4', 'webm', 'mkv'):
            self.to_screen('Subtitles can only be embedded in mp4, webm or mkv files')
            return [], information
        subtitles = information.get('requested_subtitles')
        if not subtitles:
            self.to_screen('There aren\'t any subtitles to embed')
            return [], information

        filename = information['filepath']
        if information.get('duration') and self._duration_mismatch(
                self._get_real_video_duration(information, False), information['duration']):
            self.to_screen(f'Skipping {self.pp_key()} since the real and expected durations mismatch')
            return [], information

        ext = information['ext']
        sub_langs, sub_names, sub_filenames = [], [], []
        webm_vtt_warn = False
        mp4_ass_warn = False

        for lang, sub_info in subtitles.items():
            if not os.path.exists(sub_info.get('filepath', '')):
                self.report_warning(f'Skipping embedding {lang} subtitle because the file is missing')
                continue
            sub_ext = sub_info['ext']
            if sub_ext == 'json':
                self.report_warning('JSON subtitles cannot be embedded')
            elif ext != 'webm' or ext == 'webm' and sub_ext == 'vtt':
                sub_langs.append(lang)
                sub_names.append(sub_info.get('name'))
                sub_filenames.append(sub_info['filepath'])
            else:
                if not webm_vtt_warn and ext == 'webm' and sub_ext != 'vtt':
                    webm_vtt_warn = True
                    self.report_warning('Only WebVTT subtitles can be embedded in webm files')
            if not mp4_ass_warn and ext == 'mp4' and sub_ext == 'ass':
                mp4_ass_warn = True
                self.report_warning('ASS subtitles cannot be properly embedded in mp4 files; expect issues')

        if not sub_langs:
            return [], information

        input_files = [filename] + sub_filenames

        opts = [
            '-c', 'copy', '-map', '0', '-dn',
            # Don't copy the existing subtitles, we may be running the
            # postprocessor a second time
            '-map', '-0:s',
            # Don't copy Apple TV chapters track, bin_data (see #19042, #19024,
            # https://trac.ffmpeg.org/ticket/6016)
            '-map', '-0:d',
        ]
        if information['ext'] == 'mp4':
            opts += ['-c:s', 'mov_text']
        for i, (lang, name) in enumerate(zip(sub_langs, sub_names)):
            opts.extend(['-map', '%d:0' % (i + 1)])
            lang_code = ISO639Utils.short2long(lang) or lang
            opts.extend(['-metadata:s:s:%d' % i, 'language=%s' % lang_code])
            if name:
                opts.extend(['-metadata:s:s:%d' % i, 'handler_name=%s' % name,
                             '-metadata:s:s:%d' % i, 'title=%s' % name])

        temp_filename = prepend_extension(filename, 'temp')
        self.to_screen('Embedding subtitles in "%s"' % filename)
        self.run_ffmpeg_multiple_files(input_files, temp_filename, opts)
        os.replace(temp_filename, filename)

        files_to_delete = [] if self._already_have_subtitle else sub_filenames
        return files_to_delete, information


class FFmpegMetadataPP(FFmpegPostProcessor):

    def __init__(self, downloader, add_metadata=True, add_chapters=True):
        FFmpegPostProcessor.__init__(self, downloader)
        self._add_metadata = add_metadata
        self._add_chapters = add_chapters

    @staticmethod
    def _options(target_ext):
        yield from ('-map', '0', '-dn')
        if target_ext == 'm4a':
            yield from ('-vn', '-acodec', 'copy')
        else:
            yield from ('-c', 'copy')

    @PostProcessor._restrict_to(images=False)
    def run(self, info):
        filename, metadata_filename = info['filepath'], None
        options = []
        if self._add_chapters and info.get('chapters'):
            metadata_filename = replace_extension(filename, 'meta')
            options.extend(self._get_chapter_opts(info['chapters'], metadata_filename))
        if self._add_metadata:
            options.extend(self._get_metadata_opts(info))

        if not options:
            self.to_screen('There isn\'t any metadata to add')
            return [], info

        temp_filename = prepend_extension(filename, 'temp')
        self.to_screen('Adding metadata to "%s"' % filename)
        self.run_ffmpeg_multiple_files(
            (filename, metadata_filename), temp_filename,
            itertools.chain(self._options(info['ext']), *options))
        if metadata_filename:
            os.remove(metadata_filename)
        os.replace(temp_filename, filename)
        return [], info

    @staticmethod
    def _get_chapter_opts(chapters, metadata_filename):
        with io.open(metadata_filename, 'wt', encoding='utf-8') as f:
            def ffmpeg_escape(text):
                return re.sub(r'([\\=;#\n])', r'\\\1', text)

            metadata_file_content = ';FFMETADATA1\n'
            for chapter in chapters:
                metadata_file_content += '[CHAPTER]\nTIMEBASE=1/1000\n'
                metadata_file_content += 'START=%d\n' % (chapter['start_time'] * 1000)
                metadata_file_content += 'END=%d\n' % (chapter['end_time'] * 1000)
                chapter_title = chapter.get('title')
                if chapter_title:
                    metadata_file_content += 'title=%s\n' % ffmpeg_escape(chapter_title)
            f.write(metadata_file_content)
        yield ('-map_metadata', '1')

    def _get_metadata_opts(self, info):
        metadata = {}
        meta_prefix = 'meta_'

        def add(meta_list, info_list=None):
            value = next((
                str(info[key]) for key in [meta_prefix] + list(variadic(info_list or meta_list))
                if info.get(key) is not None), None)
            if value not in ('', None):
                metadata.update({meta_f: value for meta_f in variadic(meta_list)})

        # See [1-4] for some info on media metadata/metadata supported
        # by ffmpeg.
        # 1. https://kdenlive.org/en/project/adding-meta-data-to-mp4-video/
        # 2. https://wiki.multimedia.cx/index.php/FFmpeg_Metadata
        # 3. https://kodi.wiki/view/Video_file_tagging

        add('title', ('track', 'title'))
        add('date', 'upload_date')
        add(('description', 'synopsis'), 'description')
        add(('purl', 'comment'), 'webpage_url')
        add('track', 'track_number')
        add('artist', ('artist', 'creator', 'uploader', 'uploader_id'))
        add('genre')
        add('album')
        add('album_artist')
        add('disc', 'disc_number')
        add('show', 'series')
        add('season_number')
        add('episode_id', ('episode', 'episode_id'))
        add('episode_sort', 'episode_number')

        for key, value in info.items():
            if value is not None and key != meta_prefix and key.startswith(meta_prefix):
                metadata[key[len(meta_prefix):]] = value

        for name, value in metadata.items():
            yield ('-metadata', f'{name}={value}')

        stream_idx = 0
        for fmt in info.get('requested_formats') or []:
            stream_count = 2 if 'none' not in (fmt.get('vcodec'), fmt.get('acodec')) else 1
            if fmt.get('language'):
                lang = ISO639Utils.short2long(fmt['language']) or fmt['language']
                for i in range(stream_count):
                    yield ('-metadata:s:%d' % (stream_idx + i), 'language=%s' % lang)
            stream_idx += stream_count

        if ('no-attach-info-json' not in self.get_param('compat_opts', [])
                and '__infojson_filename' in info and info['ext'] in ('mkv', 'mka')):
            old_stream, new_stream = self.get_stream_number(info['filepath'], ('tags', 'mimetype'), 'application/json')
            if old_stream is not None:
                yield ('-map', '-0:%d' % old_stream)
                new_stream -= 1

            yield ('-attach', info['__infojson_filename'],
                   '-metadata:s:%d' % new_stream, 'mimetype=application/json')


class FFmpegMergerPP(FFmpegPostProcessor):
    @PostProcessor._restrict_to(images=False)
    def run(self, info):
        filename = info['filepath']
        temp_filename = prepend_extension(filename, 'temp')
        args = ['-c', 'copy']
        audio_streams = 0
        for (i, fmt) in enumerate(info['requested_formats']):
            if fmt.get('acodec') != 'none':
                args.extend(['-map', f'{i}:a:0'])
                aac_fixup = fmt['protocol'].startswith('m3u8') and self.get_audio_codec(fmt['filepath']) == 'aac'
                if aac_fixup:
                    args.extend([f'-bsf:a:{audio_streams}', 'aac_adtstoasc'])
                audio_streams += 1
            if fmt.get('vcodec') != 'none':
                args.extend(['-map', '%u:v:0' % (i)])
        self.to_screen('Merging formats into "%s"' % filename)
        self.run_ffmpeg_multiple_files(info['__files_to_merge'], temp_filename, args)
        os.rename(encodeFilename(temp_filename), encodeFilename(filename))
        return info['__files_to_merge'], info

    def can_merge(self):
        # TODO: figure out merge-capable ffmpeg version
        if self.basename != 'avconv':
            return True

        required_version = '10-0'
        if is_outdated_version(
                self._versions[self.basename], required_version):
            warning = ('Your copy of %s is outdated and unable to properly mux separate video and audio files, '
                       'yt-dlp will download single file media. '
                       'Update %s to version %s or newer to fix this.') % (
                           self.basename, self.basename, required_version)
            self.report_warning(warning)
            return False
        return True


class FFmpegFixupPostProcessor(FFmpegPostProcessor):
    def _fixup(self, msg, filename, options):
        temp_filename = prepend_extension(filename, 'temp')

        self.to_screen(f'{msg} of "{filename}"')
        self.run_ffmpeg(filename, temp_filename, options)

        os.replace(temp_filename, filename)


class FFmpegFixupStretchedPP(FFmpegFixupPostProcessor):
    @PostProcessor._restrict_to(images=False, audio=False)
    def run(self, info):
        stretched_ratio = info.get('stretched_ratio')
        if stretched_ratio not in (None, 1):
            self._fixup('Fixing aspect ratio', info['filepath'], [
                '-c', 'copy', '-map', '0', '-dn', '-aspect', '%f' % stretched_ratio])
        return [], info


class FFmpegFixupM4aPP(FFmpegFixupPostProcessor):
    @PostProcessor._restrict_to(images=False, video=False)
    def run(self, info):
        if info.get('container') == 'm4a_dash':
            self._fixup('Correcting container', info['filepath'], [
                '-c', 'copy', '-map', '0', '-dn', '-f', 'mp4'])
        return [], info


class FFmpegFixupM3u8PP(FFmpegFixupPostProcessor):
    @PostProcessor._restrict_to(images=False)
    def run(self, info):
        if self.get_audio_codec(info['filepath']) == 'aac':
            self._fixup('Fixing malformed AAC bitstream', info['filepath'], [
                '-c', 'copy', '-map', '0', '-dn', '-f', 'mp4', '-bsf:a', 'aac_adtstoasc'])
        return [], info


class FFmpegFixupTimestampPP(FFmpegFixupPostProcessor):

    def __init__(self, downloader=None, trim=0.001):
        # "trim" should be used when the video contains unintended packets
        super(FFmpegFixupTimestampPP, self).__init__(downloader)
        assert isinstance(trim, (int, float))
        self.trim = str(trim)

    @PostProcessor._restrict_to(images=False)
    def run(self, info):
        if not self._features.get('setts'):
            self.report_warning(
                'A re-encode is needed to fix timestamps in older versions of ffmpeg. '
                'Please install ffmpeg 4.4 or later to fixup without re-encoding')
            opts = ['-vf', 'setpts=PTS-STARTPTS']
        else:
            opts = ['-c', 'copy', '-bsf', 'setts=ts=TS-STARTPTS']
        self._fixup('Fixing frame timestamp', info['filepath'], opts + ['-map', '0', '-dn', '-ss', self.trim])
        return [], info


class FFmpegFixupDurationPP(FFmpegFixupPostProcessor):
    @PostProcessor._restrict_to(images=False)
    def run(self, info):
        self._fixup('Fixing video duration', info['filepath'], ['-c', 'copy', '-map', '0', '-dn'])
        return [], info


class FFmpegSubtitlesConvertorPP(FFmpegPostProcessor):
    SUPPORTED_EXTS = ('srt', 'vtt', 'ass', 'lrc')

    def __init__(self, downloader=None, format=None):
        super(FFmpegSubtitlesConvertorPP, self).__init__(downloader)
        self.format = format

    def run(self, info):
        subs = info.get('requested_subtitles')
        new_ext = self.format
        new_format = new_ext
        if new_format == 'vtt':
            new_format = 'webvtt'
        if subs is None:
            self.to_screen('There aren\'t any subtitles to convert')
            return [], info
        self.to_screen('Converting subtitles')
        sub_filenames = []
        for lang, sub in subs.items():
            if not os.path.exists(sub.get('filepath', '')):
                self.report_warning(f'Skipping embedding {lang} subtitle because the file is missing')
                continue
            ext = sub['ext']
            if ext == new_ext:
                self.to_screen('Subtitle file for %s is already in the requested format' % new_ext)
                continue
            elif ext == 'json':
                self.to_screen(
                    'You have requested to convert json subtitles into another format, '
                    'which is currently not possible')
                continue
            old_file = sub['filepath']
            sub_filenames.append(old_file)
            new_file = replace_extension(old_file, new_ext)

            if ext in ('dfxp', 'ttml', 'tt'):
                self.report_warning(
                    'You have requested to convert dfxp (TTML) subtitles into another format, '
                    'which results in style information loss')

                dfxp_file = old_file
                srt_file = replace_extension(old_file, 'srt')

                with open(dfxp_file, 'rb') as f:
                    srt_data = dfxp2srt(f.read())

                with io.open(srt_file, 'wt', encoding='utf-8') as f:
                    f.write(srt_data)
                old_file = srt_file

                subs[lang] = {
                    'ext': 'srt',
                    'data': srt_data,
                    'filepath': srt_file,
                }

                if new_ext == 'srt':
                    continue
                else:
                    sub_filenames.append(srt_file)

            self.run_ffmpeg(old_file, new_file, ['-f', new_format])

            with io.open(new_file, 'rt', encoding='utf-8') as f:
                subs[lang] = {
                    'ext': new_ext,
                    'data': f.read(),
                    'filepath': new_file,
                }

            info['__files_to_move'][new_file] = replace_extension(
                info['__files_to_move'][sub['filepath']], new_ext)

        return sub_filenames, info


class FFmpegSplitChaptersPP(FFmpegPostProcessor):
    def __init__(self, downloader, force_keyframes=False):
        FFmpegPostProcessor.__init__(self, downloader)
        self._force_keyframes = force_keyframes

    def _prepare_filename(self, number, chapter, info):
        info = info.copy()
        info.update({
            'section_number': number,
            'section_title': chapter.get('title'),
            'section_start': chapter.get('start_time'),
            'section_end': chapter.get('end_time'),
        })
        return self._downloader.prepare_filename(info, 'chapter')

    def _ffmpeg_args_for_chapter(self, number, chapter, info):
        destination = self._prepare_filename(number, chapter, info)
        if not self._downloader._ensure_dir_exists(encodeFilename(destination)):
            return

        chapter['filepath'] = destination
        self.to_screen('Chapter %03d; Destination: %s' % (number, destination))
        return (
            destination,
            ['-ss', compat_str(chapter['start_time']),
             '-t', compat_str(chapter['end_time'] - chapter['start_time'])])

    @PostProcessor._restrict_to(images=False)
    def run(self, info):
        chapters = info.get('chapters') or []
        if not chapters:
            self.to_screen('Chapter information is unavailable')
            return [], info

        in_file = info['filepath']
        if self._force_keyframes and len(chapters) > 1:
            in_file = self.force_keyframes(in_file, (c['start_time'] for c in chapters))
        self.to_screen('Splitting video by chapters; %d chapters found' % len(chapters))
        for idx, chapter in enumerate(chapters):
            destination, opts = self._ffmpeg_args_for_chapter(idx + 1, chapter, info)
            self.real_run_ffmpeg([(in_file, opts)], [(destination, ['-c', 'copy'])])
        if in_file != info['filepath']:
            os.remove(in_file)
        return [], info


class FFmpegThumbnailsConvertorPP(FFmpegPostProcessor):
    SUPPORTED_EXTS = ('jpg', 'png')

    def __init__(self, downloader=None, format=None):
        super(FFmpegThumbnailsConvertorPP, self).__init__(downloader)
        self.format = format

    @staticmethod
    def is_webp(path):
        with open(encodeFilename(path), 'rb') as f:
            b = f.read(12)
        return b[0:4] == b'RIFF' and b[8:] == b'WEBP'

    def fixup_webp(self, info, idx=-1):
        thumbnail_filename = info['thumbnails'][idx]['filepath']
        _, thumbnail_ext = os.path.splitext(thumbnail_filename)
        if thumbnail_ext:
            thumbnail_ext = thumbnail_ext[1:].lower()
            if thumbnail_ext != 'webp' and self.is_webp(thumbnail_filename):
                self.to_screen('Correcting thumbnail "%s" extension to webp' % thumbnail_filename)
                webp_filename = replace_extension(thumbnail_filename, 'webp')
                os.replace(thumbnail_filename, webp_filename)
                info['thumbnails'][idx]['filepath'] = webp_filename
                info['__files_to_move'][webp_filename] = replace_extension(
                    info['__files_to_move'].pop(thumbnail_filename), 'webp')

    @staticmethod
    def _options(target_ext):
        if target_ext == 'jpg':
            return ['-bsf:v', 'mjpeg2jpeg']
        return []

    def convert_thumbnail(self, thumbnail_filename, target_ext):
        thumbnail_conv_filename = replace_extension(thumbnail_filename, target_ext)

        self.to_screen('Converting thumbnail "%s" to %s' % (thumbnail_filename, target_ext))
        self.real_run_ffmpeg(
            [(thumbnail_filename, ['-f', 'image2', '-pattern_type', 'none'])],
            [(thumbnail_conv_filename.replace('%', '%%'), self._options(target_ext))])
        return thumbnail_conv_filename

    def run(self, info):
        files_to_delete = []
        has_thumbnail = False

        for idx, thumbnail_dict in enumerate(info['thumbnails']):
            if 'filepath' not in thumbnail_dict:
                continue
            has_thumbnail = True
            self.fixup_webp(info, idx)
            original_thumbnail = thumbnail_dict['filepath']
            _, thumbnail_ext = os.path.splitext(original_thumbnail)
            if thumbnail_ext:
                thumbnail_ext = thumbnail_ext[1:].lower()
            if thumbnail_ext == 'jpeg':
                thumbnail_ext = 'jpg'
            if thumbnail_ext == self.format:
                self.to_screen('Thumbnail "%s" is already in the requested format' % original_thumbnail)
                continue
            thumbnail_dict['filepath'] = self.convert_thumbnail(original_thumbnail, self.format)
            files_to_delete.append(original_thumbnail)
            info['__files_to_move'][thumbnail_dict['filepath']] = replace_extension(
                info['__files_to_move'][original_thumbnail], self.format)

        if not has_thumbnail:
            self.to_screen('There aren\'t any thumbnails to convert')
        return files_to_delete, info