nalu_reader.cc

// Copyright 2016 Google LLC. All rights reserved.
//
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file or at
// https://developers.google.com/open-source/licenses/bsd
 
#include <packager/media/codecs/nalu_reader.h>
 
#include <cstddef>
#include <cstdint>
#include <iostream>
#include <vector>
 
#include <absl/log/check.h>
#include <absl/log/log.h>
 
#include <packager/media/base/buffer_reader.h>
#include <packager/media/base/decrypt_config.h>
 
namespace shaka {
namespace media {
 
namespace {
inline bool IsStartCode(const uint8_t* data) {
  return data[0] == 0x00 && data[1] == 0x00 && data[2] == 0x01;
}
 
// Edits |subsamples| given the number of consumed bytes.
void UpdateSubsamples(uint64_t consumed_bytes,
                      std::vector<SubsampleEntry>* subsamples) {
  if (consumed_bytes == 0 || subsamples->empty()) {
    return;
  }
  size_t num_entries_to_delete = 0;
  for (SubsampleEntry& subsample : *subsamples) {
    if (subsample.clear_bytes > consumed_bytes) {
      subsample.clear_bytes -= consumed_bytes;
      consumed_bytes = 0;
      break;
    }
    consumed_bytes -= subsample.clear_bytes;
    subsample.clear_bytes = 0;
 
    if (subsample.cipher_bytes > consumed_bytes) {
      subsample.cipher_bytes -= consumed_bytes;
      consumed_bytes = 0;
      break;
    }
    consumed_bytes -= subsample.cipher_bytes;
    subsample.cipher_bytes = 0;
    ++num_entries_to_delete;
  }
 
  subsamples->erase(subsamples->begin(),
                    subsamples->begin() + num_entries_to_delete);
}
 
bool IsNaluLengthEncrypted(uint8_t nalu_length_size,
                           const std::vector<SubsampleEntry>& subsamples) {
  if (subsamples.empty())
    return false;
 
  for (const SubsampleEntry& subsample : subsamples) {
    if (subsample.clear_bytes >= nalu_length_size) {
      return false;
    }
    nalu_length_size -= subsample.clear_bytes;
    if (subsample.cipher_bytes > 0) {
      return true;
    }
  }
  // Ran out of subsamples. Assume the rest is in the clear.
  return false;
}
}  // namespace
 
Nalu::Nalu() = default;
 
bool Nalu::Initialize(CodecType type, const uint8_t* data, uint64_t size) {
  if (type == Nalu::kH264) {
    return InitializeFromH264(data, size);
  } else {
    DCHECK_EQ(Nalu::kH265, type);
    return InitializeFromH265(data, size);
  }
}
 
// ITU-T H.264 (02/2014) 7.4.1 NAL unit semantics
bool Nalu::InitializeFromH264(const uint8_t* data, uint64_t size) {
  DCHECK(data);
  if (size == 0)
    return false;
  const uint8_t header = data[0];
  if ((header & 0x80) != 0) {
    LOG(WARNING) << "forbidden_zero_bit shall be equal to 0 (header 0x"
                 << std::hex << static_cast<int>(header) << ").";
    return false;
  }
 
  data_ = data;
  header_size_ = 1;
  payload_size_ = size - header_size_;
  ref_idc_ = (header >> 5) & 0x3;
  type_ = header & 0x1F;
 
  // Reserved NAL units are not treated as valid NAL units here.
  if (type_ == Nalu::H264_Unspecified || type_ == Nalu::H264_Reserved17 ||
      type_ == Nalu::H264_Reserved18 || type_ >= Nalu::H264_Reserved22) {
    VLOG(1) << "Unspecified or reserved nal_unit_type " << type_
            << " (header 0x" << std::hex << static_cast<int>(header) << ").";
    // Allow reserved NAL units. Some encoders and extended codecs use the
    // reserved NAL units to carry their private data.
  } else if (type_ == Nalu::H264_IDRSlice || type_ == Nalu::H264_SPS ||
             type_ == Nalu::H264_SPSExtension ||
             type_ == Nalu::H264_SubsetSPS || type_ == Nalu::H264_PPS) {
    if (ref_idc_ == 0) {
      LOG(WARNING) << "nal_ref_idc shall not be equal to 0 for nalu type "
                   << type_ << " (header 0x" << std::hex
                   << static_cast<int>(header) << ").";
      return false;
    }
  } else if (type_ == Nalu::H264_SEIMessage ||
             (type_ >= Nalu::H264_AUD && type_ <= Nalu::H264_FillerData)) {
    if (ref_idc_ != 0) {
      LOG(WARNING) << "nal_ref_idc shall be equal to 0 for nalu type " << type_
                   << " (header 0x" << std::hex << static_cast<int>(header)
                   << ").";
      return false;
    }
  }
 
  is_aud_ = type_ == H264_AUD;
  is_vcl_ = (type_ >= Nalu::H264_NonIDRSlice && type_ <= Nalu::H264_IDRSlice);
  is_video_slice_ =
      (type_ == Nalu::H264_NonIDRSlice || type_ == Nalu::H264_IDRSlice);
  can_start_access_unit_ =
      (is_vcl_ || type_ == Nalu::H264_AUD || type_ == Nalu::H264_SPS ||
       type_ == Nalu::H264_PPS || type_ == Nalu::H264_SEIMessage ||
       (type_ >= Nalu::H264_PrefixNALUnit && type_ <= Nalu::H264_Reserved18));
  return true;
}
 
// ITU-T H.265 (04/2015) 7.4.2.2 NAL unit header semantics
bool Nalu::InitializeFromH265(const uint8_t* data, uint64_t size) {
  DCHECK(data);
  if (size < 2)
    return false;
  const uint16_t header = (data[0] << 8) | data[1];
  if ((header & 0x8000) != 0) {
    LOG(WARNING) << "forbidden_zero_bit shall be equal to 0 (header 0x"
                 << std::hex << header << ").";
    return false;
  }
 
  data_ = data;
  header_size_ = 2;
  payload_size_ = size - header_size_;
 
  type_ = (header >> 9) & 0x3F;
  nuh_layer_id_ = (header >> 3) & 0x3F;
  const int nuh_temporal_id_plus1 = header & 0x7;
  if (nuh_temporal_id_plus1 == 0) {
    LOG(WARNING) << "nul_temporal_id_plus1 shall not be equal to 0 (header 0x"
                 << std::hex << header << ").";
    return false;
  }
  nuh_temporal_id_ = nuh_temporal_id_plus1 - 1;
 
  if (type_ == Nalu::H265_EOB && nuh_layer_id_ != 0) {
    LOG(WARNING) << "nuh_layer_id shall be equal to 0 for nalu type " << type_
                 << " (header 0x" << std::hex << header << ").";
    return false;
  }
 
  // Reserved NAL units are not treated as valid NAL units here.
  if ((type_ >= Nalu::H265_RSV_VCL_N10 && type_ <= Nalu::H265_RSV_VCL_R15) ||
      (type_ >= Nalu::H265_RSV_IRAP_VCL22 && type_ < Nalu::H265_RSV_VCL31) ||
      (type_ >= Nalu::H265_RSV_NVCL41)) {
    VLOG(1) << "Unspecified or reserved nal_unit_type " << type_
            << " (header 0x" << std::hex << header << ").";
    // Allow reserved NAL units. Some encoders and extended codecs use the
    // reserved NAL units to carry their private data. For example, Dolby Vision
    // uses NAL unit type 62.
  } else if ((type_ >= Nalu::H265_BLA_W_LP &&
              type_ <= Nalu::H265_RSV_IRAP_VCL23) ||
             type_ == Nalu::H265_VPS || type_ == Nalu::H265_SPS ||
             type_ == Nalu::H265_EOS || type_ == Nalu::H265_EOB) {
    if (nuh_temporal_id_ != 0) {
      LOG(WARNING) << "TemporalId shall be equal to 0 for nalu type " << type_
                   << " (header 0x" << std::hex << header << ").";
      return false;
    }
  } else if (type_ == Nalu::H265_TSA_N || type_ == Nalu::H265_TSA_R ||
             (nuh_layer_id_ == 0 &&
              (type_ == Nalu::H265_STSA_N || type_ == Nalu::H265_STSA_R))) {
    if (nuh_temporal_id_ == 0) {
      LOG(WARNING) << "TemporalId shall not be equal to 0 for nalu type "
                   << type_ << " (header 0x" << std::hex << header << ").";
      return false;
    }
  }
 
  is_aud_ = type_ == H265_AUD;
  is_vcl_ = type_ >= Nalu::H265_TRAIL_N && type_ <= Nalu::H265_RSV_VCL31;
  is_video_slice_ = is_vcl_;
  can_start_access_unit_ =
      nuh_layer_id_ == 0 &&
      (is_vcl_ || type_ == Nalu::H265_AUD || type_ == Nalu::H265_VPS ||
       type_ == Nalu::H265_SPS || type_ == Nalu::H265_PPS ||
       type_ == Nalu::H265_PREFIX_SEI ||
       (type_ >= Nalu::H265_RSV_NVCL41 && type_ <= Nalu::H265_RSV_NVCL44) ||
       (type_ >= Nalu::H265_UNSPEC48 && type_ <= Nalu::H265_UNSPEC55));
  return true;
}
 
NaluReader::NaluReader(Nalu::CodecType type,
                       uint8_t nal_length_size,
                       const uint8_t* stream,
                       uint64_t stream_size)
    : NaluReader(type,
                 nal_length_size,
                 stream,
                 stream_size,
                 std::vector<SubsampleEntry>()) {}
 
NaluReader::NaluReader(Nalu::CodecType type,
                       uint8_t nal_length_size,
                       const uint8_t* stream,
                       uint64_t stream_size,
                       const std::vector<SubsampleEntry>& subsamples)
    : stream_(stream),
      stream_size_(stream_size),
      nalu_type_(type),
      nalu_length_size_(nal_length_size),
      format_(nal_length_size == 0 ? kAnnexbByteStreamFormat
                                   : kNalUnitStreamFormat),
      subsamples_(subsamples) {
  DCHECK(stream);
}
 
NaluReader::~NaluReader() {}
 
NaluReader::Result NaluReader::Advance(Nalu* nalu) {
  if (stream_size_ <= 0)
    return NaluReader::kEOStream;
 
  uint8_t nalu_length_size_or_start_code_size;
  uint64_t nalu_length;
  if (format_ == kAnnexbByteStreamFormat) {
    // This will move |stream_| to the start code.
    uint64_t nalu_length_with_header;
    if (!LocateNaluByStartCode(&nalu_length_with_header,
                               &nalu_length_size_or_start_code_size)) {
      LOG(ERROR) << "Could not find next NALU, bytes left in stream: "
                 << stream_size_;
      // This is actually an error.  Since we always move to past the end of
      // each NALU, if there is no next start code, then this is the first call
      // and there are no start codes in the stream.
      return NaluReader::kInvalidStream;
    }
    nalu_length = nalu_length_with_header - nalu_length_size_or_start_code_size;
  } else {
    BufferReader reader(stream_, stream_size_);
    if (IsNaluLengthEncrypted(nalu_length_size_, subsamples_)) {
      LOG(ERROR) << "NALU length is encrypted.";
      return NaluReader::kInvalidStream;
    }
    if (!reader.ReadNBytesInto8(&nalu_length, nalu_length_size_))
      return NaluReader::kInvalidStream;
    nalu_length_size_or_start_code_size = nalu_length_size_;
 
    if (nalu_length + nalu_length_size_ > stream_size_) {
      LOG(ERROR) << "NALU length exceeds stream size: " << stream_size_ << " < "
                 << nalu_length;
      return NaluReader::kInvalidStream;
    }
    if (nalu_length == 0) {
      LOG(ERROR) << "NALU size 0";
      return NaluReader::kInvalidStream;
    }
  }
 
  const uint8_t* nalu_data = stream_ + nalu_length_size_or_start_code_size;
  if (!nalu->Initialize(nalu_type_, nalu_data, nalu_length))
    return NaluReader::kInvalidStream;
 
  // Move parser state to after this NALU, so next time Advance
  // is called, we will effectively be skipping it.
  stream_ += nalu_length_size_or_start_code_size + nalu_length;
  stream_size_ -= nalu_length_size_or_start_code_size + nalu_length;
  UpdateSubsamples(nalu_length_size_or_start_code_size + nalu_length,
                   &subsamples_);
 
  DVLOG(4) << "NALU type: " << static_cast<int>(nalu->type())
           << " at: " << reinterpret_cast<const void*>(nalu->data())
           << " data size: " << nalu->payload_size();
 
  return NaluReader::kOk;
}
 
bool NaluReader::StartsWithStartCode() {
  if (stream_size_ >= 3) {
    if (IsStartCode(stream_))
      return true;
  }
  if (stream_size_ >= 4) {
    if (stream_[0] == 0x00 && IsStartCode(stream_ + 1))
      return true;
  }
  return false;
}
 
// static
bool NaluReader::FindStartCode(const uint8_t* data,
                               uint64_t data_size,
                               uint64_t* offset,
                               uint8_t* start_code_size) {
  uint64_t bytes_left = data_size;
 
  while (bytes_left >= 3) {
    if (IsStartCode(data)) {
      // Found three-byte start code, set pointer at its beginning.
      *offset = data_size - bytes_left;
      *start_code_size = 3;
 
      // If there is a zero byte before this start code,
      // then it's actually a four-byte start code, so backtrack one byte.
      if (*offset > 0 && *(data - 1) == 0x00) {
        --(*offset);
        ++(*start_code_size);
      }
 
      return true;
    }
 
    ++data;
    --bytes_left;
  }
 
  // End of data: offset is pointing to the first byte that was not considered
  // as a possible start of a start code.
  *offset = data_size - bytes_left;
  *start_code_size = 0;
  return false;
}
 
// static
bool NaluReader::FindStartCodeInClearRange(
    const uint8_t* data,
    uint64_t data_size,
    uint64_t* offset,
    uint8_t* start_code_size,
    const std::vector<SubsampleEntry>& subsamples) {
  if (subsamples.empty()) {
    return FindStartCode(data, data_size, offset, start_code_size);
  }
 
  uint64_t current_offset = 0;
  for (const SubsampleEntry& subsample : subsamples) {
    uint16_t clear_bytes = subsample.clear_bytes;
    if (current_offset + clear_bytes > data_size) {
      LOG(WARNING) << "The sum of subsample sizes is greater than data_size.";
      clear_bytes = data_size - current_offset;
    }
 
    // Note that calling FindStartCode() here should get the correct
    // start_code_size, even tho data + current_offset may be in the middle of
    // the buffer because data + current_offset - 1 is either it shouldn't be
    // accessed because it's data - 1 or it is encrypted.
    const bool found_start_code = FindStartCode(
        data + current_offset, clear_bytes, offset, start_code_size);
    if (found_start_code) {
      *offset += current_offset;
      return true;
    }
    const uint64_t subsample_size =
        subsample.clear_bytes + subsample.cipher_bytes;
    current_offset += subsample_size;
    if (current_offset > data_size) {
      // Assign data_size here so that the returned offset points to the end of
      // the data.
      current_offset = data_size;
      LOG(WARNING) << "The sum of subsamples is greater than data_size.";
      break;
    }
  }
 
  // If there is more that's not specified by the subsample entries, assume it
  // is in the clear.
  if (current_offset < data_size) {
    const bool found_start_code =
        FindStartCode(data + current_offset, data_size - current_offset, offset,
                      start_code_size);
    *offset += current_offset;
    return found_start_code;
  }
 
  // End of data: offset is pointing to the first byte that was not considered
  // as a possible start of a start code.
  *offset = current_offset;
  *start_code_size = 0;
  return false;
}
 
bool NaluReader::LocateNaluByStartCode(uint64_t* nalu_size,
                                       uint8_t* start_code_size) {
  // Find the start code of next NALU.
  uint64_t nalu_start_off = 0;
  uint8_t annexb_start_code_size = 0;
  if (!FindStartCodeInClearRange(stream_, stream_size_, &nalu_start_off,
                                 &annexb_start_code_size, subsamples_)) {
    DVLOG(4) << "Could not find start code, end of stream?";
    return false;
  }
 
  // Move the stream to the beginning of the NALU (pointing at the start code).
  stream_ += nalu_start_off;
  stream_size_ -= nalu_start_off;
  // Shift the subsamples so that next call to FindStartCode() takes the updated
  // subsample info.
  UpdateSubsamples(nalu_start_off, &subsamples_);
 
  const uint8_t* nalu_data = stream_ + annexb_start_code_size;
  // This is a temporary subsample entries for finding next nalu. subsamples_
  // should not be updated below.
  std::vector<SubsampleEntry> subsamples_for_finding_next_nalu;
  if (!subsamples_.empty()) {
    subsamples_for_finding_next_nalu = subsamples_;
    UpdateSubsamples(annexb_start_code_size, &subsamples_for_finding_next_nalu);
  }
  uint64_t max_nalu_data_size = stream_size_ - annexb_start_code_size;
  if (max_nalu_data_size <= 0) {
    DVLOG(3) << "End of stream";
    return false;
  }
 
  // Find the start code of next NALU;
  // if successful, |nalu_size_without_start_code| is the number of bytes from
  // after previous start code to before this one;
  // if next start code is not found, it is still a valid NALU since there
  // are some bytes left after the first start code: all the remaining bytes
  // belong to the current NALU.
  uint64_t nalu_size_without_start_code = 0;
  uint8_t next_start_code_size = 0;
  while (true) {
    if (!FindStartCodeInClearRange(
            nalu_data, max_nalu_data_size, &nalu_size_without_start_code,
            &next_start_code_size, subsamples_for_finding_next_nalu)) {
      nalu_data += max_nalu_data_size;
      break;
    }
 
    nalu_data += nalu_size_without_start_code + next_start_code_size;
    max_nalu_data_size -= nalu_size_without_start_code + next_start_code_size;
    UpdateSubsamples(nalu_size_without_start_code + next_start_code_size,
                     &subsamples_for_finding_next_nalu);
    // If it is not a valid NAL unit, we will continue searching. This is to
    // handle the case where emulation prevention are not applied.
    Nalu nalu;
    if (nalu.Initialize(nalu_type_, nalu_data, max_nalu_data_size)) {
      nalu_data -= next_start_code_size;
      break;
    }
    LOG(WARNING) << "Seeing invalid NAL unit. Emulation prevention may not "
                    "have been applied properly. Assuming it is part of the "
                    "previous NAL unit.";
  }
  *nalu_size = nalu_data - stream_;
  *start_code_size = annexb_start_code_size;
  return true;
}
 
}  // namespace media
}  // namespace shaka