sdk/objc/components/video_codec/nalu_rewriter.cc - src.git - Git at Google

 /*
  *  Copyright (c) 2015 The WebRTC project authors. All Rights Reserved.
  *
  *  Use of this source code is governed by a BSD-style license
  *  that can be found in the LICENSE file in the root of the source
  *  tree. An additional intellectual property rights grant can be found
  *  in the file PATENTS.  All contributing project authors may
  *  be found in the AUTHORS file in the root of the source tree.
  *
  */

 #include "sdk/objc/components/video_codec/nalu_rewriter.h"

 #include <CoreFoundation/CoreFoundation.h>
 #include <memory>
 #include <vector>

 #include "rtc_base/checks.h"
 #include "rtc_base/logging.h"

 namespace webrtc {

 using H264::kAud;
 using H264::kSps;
 using H264::NaluIndex;
 using H264::NaluType;
 using H264::ParseNaluType;

 const char kAnnexBHeaderBytes[4] = {0, 0, 0, 1};
 const size_t kAvccHeaderByteSize = sizeof(uint32_t);

 bool H264CMSampleBufferToAnnexBBuffer(
     CMSampleBufferRef avcc_sample_buffer,
     bool is_keyframe,
     rtc::Buffer* annexb_buffer,
     std::unique_ptr<RTPFragmentationHeader>* out_header) {
   RTC_DCHECK(avcc_sample_buffer);
   RTC_DCHECK(out_header);
   out_header->reset(nullptr);

   // Get format description from the sample buffer.
   CMVideoFormatDescriptionRef description =
       CMSampleBufferGetFormatDescription(avcc_sample_buffer);
   if (description == nullptr) {
     RTC_LOG(LS_ERROR) << "Failed to get sample buffer's description.";
     return false;
   }

   // Get parameter set information.
   int nalu_header_size = 0;
   size_t param_set_count = 0;
   OSStatus status = CMVideoFormatDescriptionGetH264ParameterSetAtIndex(
       description, 0, nullptr, nullptr, &param_set_count, &nalu_header_size);
   if (status != noErr) {
     RTC_LOG(LS_ERROR) << "Failed to get parameter set.";
     return false;
   }
   RTC_CHECK_EQ(nalu_header_size, kAvccHeaderByteSize);
   RTC_DCHECK_EQ(param_set_count, 2);

   // Truncate any previous data in the buffer without changing its capacity.
   annexb_buffer->SetSize(0);

   size_t nalu_offset = 0;
   std::vector<size_t> frag_offsets;
   std::vector<size_t> frag_lengths;

   // Place all parameter sets at the front of buffer.
   if (is_keyframe) {
     size_t param_set_size = 0;
     const uint8_t* param_set = nullptr;
     for (size_t i = 0; i < param_set_count; ++i) {
       status = CMVideoFormatDescriptionGetH264ParameterSetAtIndex(
           description, i, &param_set, &param_set_size, nullptr, nullptr);
       if (status != noErr) {
         RTC_LOG(LS_ERROR) << "Failed to get parameter set.";
         return false;
       }
       // Update buffer.
       annexb_buffer->AppendData(kAnnexBHeaderBytes, sizeof(kAnnexBHeaderBytes));
       annexb_buffer->AppendData(reinterpret_cast<const char*>(param_set),
                                 param_set_size);
       // Update fragmentation.
       frag_offsets.push_back(nalu_offset + sizeof(kAnnexBHeaderBytes));
       frag_lengths.push_back(param_set_size);
       nalu_offset += sizeof(kAnnexBHeaderBytes) + param_set_size;
     }
   }

   // Get block buffer from the sample buffer.
   CMBlockBufferRef block_buffer =
       CMSampleBufferGetDataBuffer(avcc_sample_buffer);
   if (block_buffer == nullptr) {
     RTC_LOG(LS_ERROR) << "Failed to get sample buffer's block buffer.";
     return false;
   }
   CMBlockBufferRef contiguous_buffer = nullptr;
   // Make sure block buffer is contiguous.
   if (!CMBlockBufferIsRangeContiguous(block_buffer, 0, 0)) {
     status = CMBlockBufferCreateContiguous(
         nullptr, block_buffer, nullptr, nullptr, 0, 0, 0, &contiguous_buffer);
     if (status != noErr) {
       RTC_LOG(LS_ERROR) << "Failed to flatten non-contiguous block buffer: "
                         << status;
       return false;
     }
   } else {
     contiguous_buffer = block_buffer;
     // Retain to make cleanup easier.
     CFRetain(contiguous_buffer);
     block_buffer = nullptr;
   }

   // Now copy the actual data.
   char* data_ptr = nullptr;
   size_t block_buffer_size = CMBlockBufferGetDataLength(contiguous_buffer);
   status = CMBlockBufferGetDataPointer(contiguous_buffer, 0, nullptr, nullptr,
                                        &data_ptr);
   if (status != noErr) {
     RTC_LOG(LS_ERROR) << "Failed to get block buffer data.";
     CFRelease(contiguous_buffer);
     return false;
   }
   size_t bytes_remaining = block_buffer_size;
   while (bytes_remaining > 0) {
     // The size type here must match |nalu_header_size|, we expect 4 bytes.
     // Read the length of the next packet of data. Must convert from big endian
     // to host endian.
     RTC_DCHECK_GE(bytes_remaining, (size_t)nalu_header_size);
     uint32_t* uint32_data_ptr = reinterpret_cast<uint32_t*>(data_ptr);
     uint32_t packet_size = CFSwapInt32BigToHost(*uint32_data_ptr);
     // Update buffer.
     annexb_buffer->AppendData(kAnnexBHeaderBytes, sizeof(kAnnexBHeaderBytes));
     annexb_buffer->AppendData(data_ptr + nalu_header_size, packet_size);
     // Update fragmentation.
     frag_offsets.push_back(nalu_offset + sizeof(kAnnexBHeaderBytes));
     frag_lengths.push_back(packet_size);
     nalu_offset += sizeof(kAnnexBHeaderBytes) + packet_size;

     size_t bytes_written = packet_size + sizeof(kAnnexBHeaderBytes);
     bytes_remaining -= bytes_written;
     data_ptr += bytes_written;
   }
   RTC_DCHECK_EQ(bytes_remaining, (size_t)0);

   std::unique_ptr<RTPFragmentationHeader> header(new RTPFragmentationHeader());
   header->VerifyAndAllocateFragmentationHeader(frag_offsets.size());
   RTC_DCHECK_EQ(frag_lengths.size(), frag_offsets.size());
   for (size_t i = 0; i < frag_offsets.size(); ++i) {
     header->fragmentationOffset[i] = frag_offsets[i];
     header->fragmentationLength[i] = frag_lengths[i];
     header->fragmentationPlType[i] = 0;
     header->fragmentationTimeDiff[i] = 0;
   }
   *out_header = std::move(header);
   CFRelease(contiguous_buffer);
   return true;
 }

 bool H264AnnexBBufferToCMSampleBuffer(const uint8_t* annexb_buffer,
                                       size_t annexb_buffer_size,
                                       CMVideoFormatDescriptionRef video_format,
                                       CMSampleBufferRef* out_sample_buffer) {
   RTC_DCHECK(annexb_buffer);
   RTC_DCHECK(out_sample_buffer);
   RTC_DCHECK(video_format);
   *out_sample_buffer = nullptr;

   AnnexBBufferReader reader(annexb_buffer, annexb_buffer_size);
   if (reader.SeekToNextNaluOfType(kSps)) {
     // Buffer contains an SPS NALU - skip it and the following PPS
     const uint8_t* data;
     size_t data_len;
     if (!reader.ReadNalu(&data, &data_len)) {
       RTC_LOG(LS_ERROR) << "Failed to read SPS";
       return false;
     }
     if (!reader.ReadNalu(&data, &data_len)) {
       RTC_LOG(LS_ERROR) << "Failed to read PPS";
       return false;
     }
   } else {
     // No SPS NALU - start reading from the first NALU in the buffer
     reader.SeekToStart();
   }

   // Allocate memory as a block buffer.
   // TODO(tkchin): figure out how to use a pool.
   CMBlockBufferRef block_buffer = nullptr;
   OSStatus status = CMBlockBufferCreateWithMemoryBlock(
       nullptr, nullptr, reader.BytesRemaining(), nullptr, nullptr, 0,
       reader.BytesRemaining(), kCMBlockBufferAssureMemoryNowFlag,
       &block_buffer);
   if (status != kCMBlockBufferNoErr) {
     RTC_LOG(LS_ERROR) << "Failed to create block buffer.";
     return false;
   }

   // Make sure block buffer is contiguous.
   CMBlockBufferRef contiguous_buffer = nullptr;
   if (!CMBlockBufferIsRangeContiguous(block_buffer, 0, 0)) {
     status = CMBlockBufferCreateContiguous(
         nullptr, block_buffer, nullptr, nullptr, 0, 0, 0, &contiguous_buffer);
     if (status != noErr) {
       RTC_LOG(LS_ERROR) << "Failed to flatten non-contiguous block buffer: "
                         << status;
       CFRelease(block_buffer);
       return false;
     }
   } else {
     contiguous_buffer = block_buffer;
     block_buffer = nullptr;
   }

   // Get a raw pointer into allocated memory.
   size_t block_buffer_size = 0;
   char* data_ptr = nullptr;
   status = CMBlockBufferGetDataPointer(contiguous_buffer, 0, nullptr,
                                        &block_buffer_size, &data_ptr);
   if (status != kCMBlockBufferNoErr) {
     RTC_LOG(LS_ERROR) << "Failed to get block buffer data pointer.";
     CFRelease(contiguous_buffer);
     return false;
   }
   RTC_DCHECK(block_buffer_size == reader.BytesRemaining());

   // Write Avcc NALUs into block buffer memory.
   AvccBufferWriter writer(reinterpret_cast<uint8_t*>(data_ptr),
                           block_buffer_size);
   while (reader.BytesRemaining() > 0) {
     const uint8_t* nalu_data_ptr = nullptr;
     size_t nalu_data_size = 0;
     if (reader.ReadNalu(&nalu_data_ptr, &nalu_data_size)) {
       writer.WriteNalu(nalu_data_ptr, nalu_data_size);
     }
   }

   // Create sample buffer.
   status = CMSampleBufferCreate(nullptr, contiguous_buffer, true, nullptr,
                                 nullptr, video_format, 1, 0, nullptr, 0,
                                 nullptr, out_sample_buffer);
   if (status != noErr) {
     RTC_LOG(LS_ERROR) << "Failed to create sample buffer.";
     CFRelease(contiguous_buffer);
     return false;
   }
   CFRelease(contiguous_buffer);
   return true;
 }

 CMVideoFormatDescriptionRef CreateVideoFormatDescription(
     const uint8_t* annexb_buffer,
     size_t annexb_buffer_size) {
   const uint8_t* param_set_ptrs[2] = {};
   size_t param_set_sizes[2] = {};
   AnnexBBufferReader reader(annexb_buffer, annexb_buffer_size);
   // Skip everyting before the SPS, then read the SPS and PPS
   if (!reader.SeekToNextNaluOfType(kSps)) {
     return nullptr;
   }
   if (!reader.ReadNalu(&param_set_ptrs[0], &param_set_sizes[0])) {
     RTC_LOG(LS_ERROR) << "Failed to read SPS";
     return nullptr;
   }
   if (!reader.ReadNalu(&param_set_ptrs[1], &param_set_sizes[1])) {
     RTC_LOG(LS_ERROR) << "Failed to read PPS";
     return nullptr;
   }

   // Parse the SPS and PPS into a CMVideoFormatDescription.
   CMVideoFormatDescriptionRef description = nullptr;
   OSStatus status = CMVideoFormatDescriptionCreateFromH264ParameterSets(
       kCFAllocatorDefault, 2, param_set_ptrs, param_set_sizes, 4, &description);
   if (status != noErr) {
     RTC_LOG(LS_ERROR) << "Failed to create video format description.";
     return nullptr;
   }
   return description;
 }

 AnnexBBufferReader::AnnexBBufferReader(const uint8_t* annexb_buffer,
                                        size_t length)
     : start_(annexb_buffer), length_(length) {
   RTC_DCHECK(annexb_buffer);
   offsets_ = H264::FindNaluIndices(annexb_buffer, length);
   offset_ = offsets_.begin();
 }

 AnnexBBufferReader::~AnnexBBufferReader() = default;

 bool AnnexBBufferReader::ReadNalu(const uint8_t** out_nalu,
                                   size_t* out_length) {
   RTC_DCHECK(out_nalu);
   RTC_DCHECK(out_length);
   *out_nalu = nullptr;
   *out_length = 0;

   if (offset_ == offsets_.end()) {
     return false;
   }
   *out_nalu = start_ + offset_->payload_start_offset;
   *out_length = offset_->payload_size;
   ++offset_;
   return true;
 }

 size_t AnnexBBufferReader::BytesRemaining() const {
   if (offset_ == offsets_.end()) {
     return 0;
   }
   return length_ - offset_->start_offset;
 }

 void AnnexBBufferReader::SeekToStart() {
   offset_ = offsets_.begin();
 }

 bool AnnexBBufferReader::SeekToNextNaluOfType(NaluType type) {
   for (; offset_ != offsets_.end(); ++offset_) {
     if (offset_->payload_size < 1)
       continue;
     if (ParseNaluType(*(start_ + offset_->payload_start_offset)) == type)
       return true;
   }
   return false;
 }
 AvccBufferWriter::AvccBufferWriter(uint8_t* const avcc_buffer, size_t length)
     : start_(avcc_buffer), offset_(0), length_(length) {
   RTC_DCHECK(avcc_buffer);
 }

 bool AvccBufferWriter::WriteNalu(const uint8_t* data, size_t data_size) {
   // Check if we can write this length of data.
   if (data_size + kAvccHeaderByteSize > BytesRemaining()) {
     return false;
   }
   // Write length header, which needs to be big endian.
   uint32_t big_endian_length = CFSwapInt32HostToBig(data_size);
   memcpy(start_ + offset_, &big_endian_length, sizeof(big_endian_length));
   offset_ += sizeof(big_endian_length);
   // Write data.
   memcpy(start_ + offset_, data, data_size);
   offset_ += data_size;
   return true;
 }

 size_t AvccBufferWriter::BytesRemaining() const {
   return length_ - offset_;
 }

 }  // namespace webrtc
	/*
	* Copyright (c) 2015 The WebRTC project authors. All Rights Reserved.
	*
	* Use of this source code is governed by a BSD-style license
	* that can be found in the LICENSE file in the root of the source
	* tree. An additional intellectual property rights grant can be found
	* in the file PATENTS. All contributing project authors may
	* be found in the AUTHORS file in the root of the source tree.
	*
	*/

	#include "sdk/objc/components/video_codec/nalu_rewriter.h"

	#include <CoreFoundation/CoreFoundation.h>
	#include <memory>
	#include <vector>

	#include "rtc_base/checks.h"
	#include "rtc_base/logging.h"

	namespace webrtc {

	using H264::kAud;
	using H264::kSps;
	using H264::NaluIndex;
	using H264::NaluType;
	using H264::ParseNaluType;

	const char kAnnexBHeaderBytes[4] = {0, 0, 0, 1};
	const size_t kAvccHeaderByteSize = sizeof(uint32_t);

	bool H264CMSampleBufferToAnnexBBuffer(
	CMSampleBufferRef avcc_sample_buffer,
	bool is_keyframe,
	rtc::Buffer* annexb_buffer,
	std::unique_ptr<RTPFragmentationHeader>* out_header) {
	RTC_DCHECK(avcc_sample_buffer);
	RTC_DCHECK(out_header);
	out_header->reset(nullptr);

	// Get format description from the sample buffer.
	CMVideoFormatDescriptionRef description =
	CMSampleBufferGetFormatDescription(avcc_sample_buffer);
	if (description == nullptr) {
	RTC_LOG(LS_ERROR) << "Failed to get sample buffer's description.";
	return false;
	}

	// Get parameter set information.
	int nalu_header_size = 0;
	size_t param_set_count = 0;
	OSStatus status = CMVideoFormatDescriptionGetH264ParameterSetAtIndex(
	description, 0, nullptr, nullptr, &param_set_count, &nalu_header_size);
	if (status != noErr) {
	RTC_LOG(LS_ERROR) << "Failed to get parameter set.";
	return false;
	}
	RTC_CHECK_EQ(nalu_header_size, kAvccHeaderByteSize);
	RTC_DCHECK_EQ(param_set_count, 2);

	// Truncate any previous data in the buffer without changing its capacity.
	annexb_buffer->SetSize(0);

	size_t nalu_offset = 0;
	std::vector<size_t> frag_offsets;
	std::vector<size_t> frag_lengths;

	// Place all parameter sets at the front of buffer.
	if (is_keyframe) {
	size_t param_set_size = 0;
	const uint8_t* param_set = nullptr;
	for (size_t i = 0; i < param_set_count; ++i) {
	status = CMVideoFormatDescriptionGetH264ParameterSetAtIndex(
	description, i, &param_set, &param_set_size, nullptr, nullptr);
	if (status != noErr) {
	RTC_LOG(LS_ERROR) << "Failed to get parameter set.";
	return false;
	}
	// Update buffer.
	annexb_buffer->AppendData(kAnnexBHeaderBytes, sizeof(kAnnexBHeaderBytes));
	annexb_buffer->AppendData(reinterpret_cast<const char*>(param_set),
	param_set_size);
	// Update fragmentation.
	frag_offsets.push_back(nalu_offset + sizeof(kAnnexBHeaderBytes));
	frag_lengths.push_back(param_set_size);
	nalu_offset += sizeof(kAnnexBHeaderBytes) + param_set_size;
	}
	}

	// Get block buffer from the sample buffer.
	CMBlockBufferRef block_buffer =
	CMSampleBufferGetDataBuffer(avcc_sample_buffer);
	if (block_buffer == nullptr) {
	RTC_LOG(LS_ERROR) << "Failed to get sample buffer's block buffer.";
	return false;
	}
	CMBlockBufferRef contiguous_buffer = nullptr;
	// Make sure block buffer is contiguous.
	if (!CMBlockBufferIsRangeContiguous(block_buffer, 0, 0)) {
	status = CMBlockBufferCreateContiguous(
	nullptr, block_buffer, nullptr, nullptr, 0, 0, 0, &contiguous_buffer);
	if (status != noErr) {
	RTC_LOG(LS_ERROR) << "Failed to flatten non-contiguous block buffer: "
	<< status;
	return false;
	}
	} else {
	contiguous_buffer = block_buffer;
	// Retain to make cleanup easier.
	CFRetain(contiguous_buffer);
	block_buffer = nullptr;
	}

	// Now copy the actual data.
	char* data_ptr = nullptr;
	size_t block_buffer_size = CMBlockBufferGetDataLength(contiguous_buffer);
	status = CMBlockBufferGetDataPointer(contiguous_buffer, 0, nullptr, nullptr,
	&data_ptr);
	if (status != noErr) {
	RTC_LOG(LS_ERROR) << "Failed to get block buffer data.";
	CFRelease(contiguous_buffer);
	return false;
	}
	size_t bytes_remaining = block_buffer_size;
	while (bytes_remaining > 0) {
	// The size type here must match \|nalu_header_size\|, we expect 4 bytes.
	// Read the length of the next packet of data. Must convert from big endian
	// to host endian.
	RTC_DCHECK_GE(bytes_remaining, (size_t)nalu_header_size);
	uint32_t* uint32_data_ptr = reinterpret_cast<uint32_t*>(data_ptr);
	uint32_t packet_size = CFSwapInt32BigToHost(*uint32_data_ptr);
	// Update buffer.
	annexb_buffer->AppendData(kAnnexBHeaderBytes, sizeof(kAnnexBHeaderBytes));
	annexb_buffer->AppendData(data_ptr + nalu_header_size, packet_size);
	// Update fragmentation.
	frag_offsets.push_back(nalu_offset + sizeof(kAnnexBHeaderBytes));
	frag_lengths.push_back(packet_size);
	nalu_offset += sizeof(kAnnexBHeaderBytes) + packet_size;

	size_t bytes_written = packet_size + sizeof(kAnnexBHeaderBytes);
	bytes_remaining -= bytes_written;
	data_ptr += bytes_written;
	}
	RTC_DCHECK_EQ(bytes_remaining, (size_t)0);

	std::unique_ptr<RTPFragmentationHeader> header(new RTPFragmentationHeader());
	header->VerifyAndAllocateFragmentationHeader(frag_offsets.size());
	RTC_DCHECK_EQ(frag_lengths.size(), frag_offsets.size());
	for (size_t i = 0; i < frag_offsets.size(); ++i) {
	header->fragmentationOffset[i] = frag_offsets[i];
	header->fragmentationLength[i] = frag_lengths[i];
	header->fragmentationPlType[i] = 0;
	header->fragmentationTimeDiff[i] = 0;
	}
	*out_header = std::move(header);
	CFRelease(contiguous_buffer);
	return true;
	}

	bool H264AnnexBBufferToCMSampleBuffer(const uint8_t* annexb_buffer,
	size_t annexb_buffer_size,
	CMVideoFormatDescriptionRef video_format,
	CMSampleBufferRef* out_sample_buffer) {
	RTC_DCHECK(annexb_buffer);
	RTC_DCHECK(out_sample_buffer);
	RTC_DCHECK(video_format);
	*out_sample_buffer = nullptr;

	AnnexBBufferReader reader(annexb_buffer, annexb_buffer_size);
	if (reader.SeekToNextNaluOfType(kSps)) {
	// Buffer contains an SPS NALU - skip it and the following PPS
	const uint8_t* data;
	size_t data_len;
	if (!reader.ReadNalu(&data, &data_len)) {
	RTC_LOG(LS_ERROR) << "Failed to read SPS";
	return false;
	}
	if (!reader.ReadNalu(&data, &data_len)) {
	RTC_LOG(LS_ERROR) << "Failed to read PPS";
	return false;
	}
	} else {
	// No SPS NALU - start reading from the first NALU in the buffer
	reader.SeekToStart();
	}

	// Allocate memory as a block buffer.
	// TODO(tkchin): figure out how to use a pool.
	CMBlockBufferRef block_buffer = nullptr;
	OSStatus status = CMBlockBufferCreateWithMemoryBlock(
	nullptr, nullptr, reader.BytesRemaining(), nullptr, nullptr, 0,
	reader.BytesRemaining(), kCMBlockBufferAssureMemoryNowFlag,
	&block_buffer);
	if (status != kCMBlockBufferNoErr) {
	RTC_LOG(LS_ERROR) << "Failed to create block buffer.";
	return false;
	}

	// Make sure block buffer is contiguous.
	CMBlockBufferRef contiguous_buffer = nullptr;
	if (!CMBlockBufferIsRangeContiguous(block_buffer, 0, 0)) {
	status = CMBlockBufferCreateContiguous(
	nullptr, block_buffer, nullptr, nullptr, 0, 0, 0, &contiguous_buffer);
	if (status != noErr) {
	RTC_LOG(LS_ERROR) << "Failed to flatten non-contiguous block buffer: "
	<< status;
	CFRelease(block_buffer);
	return false;
	}
	} else {
	contiguous_buffer = block_buffer;
	block_buffer = nullptr;
	}

	// Get a raw pointer into allocated memory.
	size_t block_buffer_size = 0;
	char* data_ptr = nullptr;
	status = CMBlockBufferGetDataPointer(contiguous_buffer, 0, nullptr,
	&block_buffer_size, &data_ptr);
	if (status != kCMBlockBufferNoErr) {
	RTC_LOG(LS_ERROR) << "Failed to get block buffer data pointer.";
	CFRelease(contiguous_buffer);
	return false;
	}
	RTC_DCHECK(block_buffer_size == reader.BytesRemaining());

	// Write Avcc NALUs into block buffer memory.
	AvccBufferWriter writer(reinterpret_cast<uint8_t*>(data_ptr),
	block_buffer_size);
	while (reader.BytesRemaining() > 0) {
	const uint8_t* nalu_data_ptr = nullptr;
	size_t nalu_data_size = 0;
	if (reader.ReadNalu(&nalu_data_ptr, &nalu_data_size)) {
	writer.WriteNalu(nalu_data_ptr, nalu_data_size);
	}
	}

	// Create sample buffer.
	status = CMSampleBufferCreate(nullptr, contiguous_buffer, true, nullptr,
	nullptr, video_format, 1, 0, nullptr, 0,
	nullptr, out_sample_buffer);
	if (status != noErr) {
	RTC_LOG(LS_ERROR) << "Failed to create sample buffer.";
	CFRelease(contiguous_buffer);
	return false;
	}
	CFRelease(contiguous_buffer);
	return true;
	}

	CMVideoFormatDescriptionRef CreateVideoFormatDescription(
	const uint8_t* annexb_buffer,
	size_t annexb_buffer_size) {
	const uint8_t* param_set_ptrs[2] = {};
	size_t param_set_sizes[2] = {};
	AnnexBBufferReader reader(annexb_buffer, annexb_buffer_size);
	// Skip everyting before the SPS, then read the SPS and PPS
	if (!reader.SeekToNextNaluOfType(kSps)) {
	return nullptr;
	}
	if (!reader.ReadNalu(&param_set_ptrs[0], &param_set_sizes[0])) {
	RTC_LOG(LS_ERROR) << "Failed to read SPS";
	return nullptr;
	}
	if (!reader.ReadNalu(&param_set_ptrs[1], &param_set_sizes[1])) {
	RTC_LOG(LS_ERROR) << "Failed to read PPS";
	return nullptr;
	}

	// Parse the SPS and PPS into a CMVideoFormatDescription.
	CMVideoFormatDescriptionRef description = nullptr;
	OSStatus status = CMVideoFormatDescriptionCreateFromH264ParameterSets(
	kCFAllocatorDefault, 2, param_set_ptrs, param_set_sizes, 4, &description);
	if (status != noErr) {
	RTC_LOG(LS_ERROR) << "Failed to create video format description.";
	return nullptr;
	}
	return description;
	}

	AnnexBBufferReader::AnnexBBufferReader(const uint8_t* annexb_buffer,
	size_t length)
	: start_(annexb_buffer), length_(length) {
	RTC_DCHECK(annexb_buffer);
	offsets_ = H264::FindNaluIndices(annexb_buffer, length);
	offset_ = offsets_.begin();
	}

	AnnexBBufferReader::~AnnexBBufferReader() = default;

	bool AnnexBBufferReader::ReadNalu(const uint8_t** out_nalu,
	size_t* out_length) {
	RTC_DCHECK(out_nalu);
	RTC_DCHECK(out_length);
	*out_nalu = nullptr;
	*out_length = 0;

	if (offset_ == offsets_.end()) {
	return false;
	}
	*out_nalu = start_ + offset_->payload_start_offset;
	*out_length = offset_->payload_size;
	++offset_;
	return true;
	}

	size_t AnnexBBufferReader::BytesRemaining() const {
	if (offset_ == offsets_.end()) {
	return 0;
	}
	return length_ - offset_->start_offset;
	}

	void AnnexBBufferReader::SeekToStart() {
	offset_ = offsets_.begin();
	}

	bool AnnexBBufferReader::SeekToNextNaluOfType(NaluType type) {
	for (; offset_ != offsets_.end(); ++offset_) {
	if (offset_->payload_size < 1)
	continue;
	if (ParseNaluType(*(start_ + offset_->payload_start_offset)) == type)
	return true;
	}
	return false;
	}
	AvccBufferWriter::AvccBufferWriter(uint8_t* const avcc_buffer, size_t length)
	: start_(avcc_buffer), offset_(0), length_(length) {
	RTC_DCHECK(avcc_buffer);
	}

	bool AvccBufferWriter::WriteNalu(const uint8_t* data, size_t data_size) {
	// Check if we can write this length of data.
	if (data_size + kAvccHeaderByteSize > BytesRemaining()) {
	return false;
	}
	// Write length header, which needs to be big endian.
	uint32_t big_endian_length = CFSwapInt32HostToBig(data_size);
	memcpy(start_ + offset_, &big_endian_length, sizeof(big_endian_length));
	offset_ += sizeof(big_endian_length);
	// Write data.
	memcpy(start_ + offset_, data, data_size);
	offset_ += data_size;
	return true;
	}

	size_t AvccBufferWriter::BytesRemaining() const {
	return length_ - offset_;
	}

	} // namespace webrtc