arc/codec-test/encoded_data_helper.cc

// Copyright 2019 The Chromium OS Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

// #define LOG_NDEBUG 0
#define LOG_TAG "EncodedDataHelper"

#include "arc/codec-test/encoded_data_helper.h"

#include <assert.h>
#include <string.h>

#include <utility>

#include <utils/Log.h>

namespace android {

namespace {

bool IsAnnexb3ByteStartCode(const std::string& data, size_t pos) {
  // The Annex-B 3-byte start code "\0\0\1" will be prefixed by NALUs per AU
  // except for the first one.
  return data[pos] == 0 && data[pos + 1] == 0 && data[pos + 2] == 1;
}

bool IsAnnexb4ByteStartCode(const std::string& data, size_t pos) {
  // The Annex-B 4-byte start code "\0\0\0\1" will be prefixed by first NALU per
  // AU.
  return data[pos] == 0 && data[pos + 1] == 0 && data[pos + 2] == 0 &&
         data[pos + 3] == 1;
}

// Get the next position of NALU header byte in |data| from |next_header_pos|,
// and update to |next_header_pos|. Return true if there is one; false
// otherwise.
// Note: this function should be used within an AU.
bool GetPosForNextNALUHeader(const std::string& data, size_t* next_header_pos) {
  size_t pos = *next_header_pos;

  // Annex-B 4-byte could be also found by IsAnnexb3ByteStartCode().
  while (pos + 3 <= data.size() && !IsAnnexb3ByteStartCode(data, pos)) {
    ++pos;
  }
  if (pos + 3 >= data.size())
    return false;  // No more NALUs

  // NALU header is the first byte after Annex-B start code.
  *next_header_pos = pos + 3;
  return true;
}

// For H264, return data bytes of next AU fragment in |data| from |next_pos|,
// and update the position to |next_pos|.
std::string GetBytesForNextAU(const std::string& data, size_t* next_pos) {
  // Helpful description:
  // https://en.wikipedia.org/wiki/Network_Abstraction_Layer
  size_t start_pos = *next_pos;
  size_t pos = start_pos;
  if (pos + 4 > data.size()) {
    ALOGE("Invalid AU: Start code is less than 4 bytes.\n");
    *next_pos = data.size();
    return std::string();
  }

  assert(IsAnnexb4ByteStartCode(data, pos));

  pos += 4;
  // The first 4 bytes must be Annex-B 4-byte start code for an AU.
  while (pos + 4 <= data.size() && !IsAnnexb4ByteStartCode(data, pos)) {
    ++pos;
  }
  if (pos + 3 >= data.size())
    pos = data.size();

  // Update next_pos.
  *next_pos = pos;
  return data.substr(start_pos, pos - start_pos);
}

// For VP8/9, return data bytes of next frame in |data| from |next_pos|, and
// update the position to |next_pos|.
std::string GetBytesForNextFrame(const std::string& data, size_t* next_pos) {
  // Helpful description: http://wiki.multimedia.cx/index.php?title=IVF
  size_t pos = *next_pos;
  std::string bytes;
  if (pos == 0)
    pos = 32;  // Skip IVF header.

  const uint32_t frame_size = *reinterpret_cast<const uint32_t*>(&data[pos]);
  pos += 12;  // Skip frame header.

  // Update next_pos.
  *next_pos = pos + frame_size;
  return data.substr(pos, frame_size);
}

}  // namespace

EncodedDataHelper::EncodedDataHelper(const std::string& file_path,
                                     VideoCodecType type)
    : type_(type) {
  InputFileStream input(file_path);
  if (!input.IsValid()) {
    ALOGE("Failed to open file: %s", file_path.c_str());
    return;
  }

  int file_size = input.GetLength();
  if (file_size <= 0) {
    ALOGE("Stream byte size (=%d) is invalid", file_size);
    return;
  }
  input.Rewind();

  char* read_bytes = new char[file_size];
  if (input.Read(read_bytes, file_size) != file_size) {
    ALOGE("Failed to read input stream from file to buffer.");
    return;
  }

  // Note: must assign |file_size| here otherwise the constuctor will terminate
  // copting at the first '\0' in |read_bytes|.
  std::string data(read_bytes, file_size);
  delete[] read_bytes;

  SliceToFragments(data);
}

EncodedDataHelper::~EncodedDataHelper() {}

const EncodedDataHelper::Fragment* const EncodedDataHelper::GetNextFragment() {
  if (ReachEndOfStream())
    return nullptr;
  return next_fragment_iter_++->get();
}

bool EncodedDataHelper::AtHeadOfStream() const {
  return next_fragment_iter_ == fragments_.begin();
}

bool EncodedDataHelper::ReachEndOfStream() const {
  return next_fragment_iter_ == fragments_.end();
}

void EncodedDataHelper::SliceToFragments(const std::string& data) {
  size_t next_pos = 0;
  bool seen_csd = false;
  while (next_pos < data.size()) {
    std::unique_ptr<Fragment> fragment(new Fragment());
    switch (type_) {
      case VideoCodecType::H264:
        fragment->data = GetBytesForNextAU(data, &next_pos);
        if (!ParseAUFragmentType(fragment.get()))
          continue;
        if (!seen_csd && !fragment->csd_flag)
          // Skip all AUs beforehand until we get SPS NALU.
          continue;
        seen_csd = true;
        break;
      case VideoCodecType::VP8:
      case VideoCodecType::VP9:
        fragment->data = GetBytesForNextFrame(data, &next_pos);
        break;
      default:
        ALOGE("Unknown video codec type.");
        return;
    }
    fragments_.push_back(std::move(fragment));
  }

  ALOGD("Total %zu fragments in interest from input stream.",
        NumValidFragments());
  next_fragment_iter_ = fragments_.begin();
}

bool EncodedDataHelper::ParseAUFragmentType(Fragment* fragment) {
  size_t next_header_pos = 0;
  while (GetPosForNextNALUHeader(fragment->data, &next_header_pos)) {
    // Read the NALU header (first byte) which contains unit type.
    uint8_t nalu_header = static_cast<uint8_t>(fragment->data[next_header_pos]);

    // Check forbidden_zero_bit (MSB of NALU header) is 0;
    if (nalu_header & 0x80) {
      ALOGE("NALU header forbidden_zero_bit is 1.");
      return false;
    }

    // Check NALU type ([3:7], 5-bit).
    uint8_t nalu_type = nalu_header & 0x1f;
    switch (nalu_type) {
      case NON_IDR_SLICE:
      case IDR_SLICE:
        // If AU contains both CSD and VCL NALUs (e.g. PPS + IDR_SLICE), don't
        // raise csd_flag, treat this fragment as VCL one.
        fragment->csd_flag = false;
        return true;  // fragment in interest as VCL.
      case SPS:
      case PPS:
        fragment->csd_flag = true;
        // Continue on finding the subsequent NALUs, it may have VCL data.
        break;
      default:
        // Skip uninterested NALU type.
        break;
    }
  }
  return fragment->csd_flag;  // fragment in interest as CSD.
}

}  // namespace android