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encoders/codecs/h264: Basic support for parsing NALs

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This commit is contained in:
Michael Fabian 'Xaymar' Dirks 2021-12-02 16:48:16 +01:00
parent afa47646f5
commit bc5de8061f
2 changed files with 101 additions and 0 deletions
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65
source/encoders/codecs/h264.cpp
View file

@ -20,3 +20,68 @@
// SOFTWARE.
#include "h264.hpp"
uint8_t* is_nal_start(uint8_t* ptr, uint8_t* end_ptr, size_t& size)
{
// Ensure that the remaining space actually can contain a prefix and NAL header.
if ((ptr + (3 + 1)) >= end_ptr)
return nullptr;
if (*ptr != 0x0)
return nullptr;
if (*(ptr + 1) != 0x0)
return nullptr;
// 3-Byte NAL prefix.
if (*(ptr + 2) == 0x1) {
size = 3;
return ptr + 3;
}
// 4-Byte NAL Prefix
if ((ptr + (4 + 1)) >= end_ptr)
return nullptr;
if (*(ptr + 2) != 0x0)
return nullptr;
if (*(ptr + 3) != 0x01)
return nullptr;
size = 4;
return ptr + 4;
}
uint8_t* streamfx::encoder::codec::h264::find_closest_nal(uint8_t* ptr, uint8_t* end_ptr, size_t& size)
{
for (uint8_t* seek_ptr = ptr; seek_ptr < end_ptr; seek_ptr++) {
if (auto nal_ptr = is_nal_start(seek_ptr, end_ptr, size); nal_ptr != nullptr)
return nal_ptr;
}
return nullptr;
}
uint32_t streamfx::encoder::codec::h264::get_packet_reference_count(uint8_t* ptr, uint8_t* end_ptr)
{
size_t nal_ptr_prefix = 0;
uint8_t* nal_ptr = find_closest_nal(ptr, end_ptr, nal_ptr_prefix);
while ((nal_ptr != nullptr) && (nal_ptr < end_ptr)) {
// Try and figure out the actual size of the NAL.
size_t nal_end_ptr_prefix = 0;
uint8_t* nal_end_ptr = find_closest_nal(nal_ptr, end_ptr, nal_end_ptr_prefix);
size_t nal_size = (nal_end_ptr ? nal_end_ptr : end_ptr) - nal_ptr - nal_end_ptr_prefix;
// Try and figure out the ideal priority.
switch (static_cast<nal_unit_type>((*nal_ptr) & 0x5)) {
case nal_unit_type::CODED_SLICE_NONIDR:
return (*nal_ptr >> 5) & 0x2;
case nal_unit_type::CODED_SLICE_IDR:
return (*nal_ptr >> 5) & 0x2;
default:
break;
}
// Update our NAL pointer.
nal_ptr = nal_end_ptr;
}
return std::numeric_limits<uint32_t>::max();
}

36
source/encoders/codecs/h264.hpp
View file

@ -60,4 +60,40 @@ namespace streamfx::encoder::codec::h264 {
L6_2,
UNKNOWN = -1,
};
// See ITU-T H.264
enum class nal_unit_type : uint8_t {
UNSPECIFIED = 0,
CODED_SLICE_NONIDR = 1,
CODED_SLICE_DATA_PARTITION_A = 2,
CODED_SLICE_DATA_PARTITION_B = 3,
CODED_SLICE_DATA_PARTITION_C = 4,
CODED_SLICE_IDR = 5,
SUPPLEMENTAL_ENHANCEMENT_INFORMATION = 6,
SEQUENCE_PARAMETER_SET = 7,
PICTURE_PARAMETER_SET = 8,
ACCESS_UNIT_DELIMITER = 9,
END_OF_SEQUENCE = 10,
END_OF_STREAM = 11,
FILLER_DATA = 12,
SEQUENCE_PARAMETER_SET_EXTENSION = 13,
PREFIX_NAL_UNIT = 14,
SUBSET_SEQUENCE_PARAMETER_SET = 15,
DEPTH_PARAMETER_SET = 16,
CODED_SLICE_AUXILIARY_PICTURE = 19,
CODED_SLICE_EXTENSION = 20,
CODED_SLICE_EXTENSION_DEPTH_VIEW = 21,
};
/** Search for the closest NAL unit.
*
* \param ptr Beginning of the search range.
* \param endptr End of the search range (exclusive).
*
* \return A valid pointer if a NAL was found, otherwise \ref nullptr.
*/
uint8_t* find_closest_nal(uint8_t* ptr, uint8_t* endptr, size_t& size);
uint32_t get_packet_reference_count(uint8_t* ptr, uint8_t* endptr);
} // namespace streamfx::encoder::codec::h264