root/media/formats/mpeg/mpeg_audio_stream_parser_base.cc

DEFINITIONS

1. LocateEndOfHeaders
2. audio_codec_
3. Init
4. Flush
5. ChangeState
6. ParseFrame
7. ParseIcecastHeader
8. ParseID3v1
9. ParseID3v2
10. ParseSyncSafeInt
11. FindNextValidStartCode
12. SendBuffers

// Copyright 2014 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#include "media/formats/mpeg/mpeg_audio_stream_parser_base.h"

#include "base/bind.h"
#include "base/callback_helpers.h"
#include "base/message_loop/message_loop.h"
#include "media/base/buffers.h"
#include "media/base/stream_parser_buffer.h"
#include "media/base/text_track_config.h"
#include "media/base/video_decoder_config.h"

namespace media {

static const uint32 kICYStartCode = 0x49435920; // 'ICY '

// Arbitrary upper bound on the size of an IceCast header before it
// triggers an error.
static const int kMaxIcecastHeaderSize = 4096;

static const uint32 kID3StartCodeMask = 0xffffff00;
static const uint32 kID3v1StartCode = 0x54414700; // 'TAG\0'
static const int kID3v1Size = 128;
static const int kID3v1ExtendedSize = 227;
static const uint32 kID3v2StartCode = 0x49443300; // 'ID3\0'

static int LocateEndOfHeaders(const uint8_t* buf, int buf_len, int i) {
  bool was_lf = false;
  char last_c = '\0';
  for (; i < buf_len; ++i) {
    char c = buf[i];
    if (c == '\n') {
      if (was_lf)
        return i + 1;
      was_lf = true;
    } else if (c != '\r' || last_c != '\n') {
      was_lf = false;
    }
    last_c = c;
  }
  return -1;
}

MPEGAudioStreamParserBase::MPEGAudioStreamParserBase(uint32 start_code_mask,
                                                     AudioCodec audio_codec)
    : state_(UNINITIALIZED),
      in_media_segment_(false),
      start_code_mask_(start_code_mask),
      audio_codec_(audio_codec) {}

MPEGAudioStreamParserBase::~MPEGAudioStreamParserBase() {}

void MPEGAudioStreamParserBase::Init(const InitCB& init_cb,
                                     const NewConfigCB& config_cb,
                                     const NewBuffersCB& new_buffers_cb,
                                     bool ignore_text_tracks,
                                     const NeedKeyCB& need_key_cb,
                                     const NewMediaSegmentCB& new_segment_cb,
                                     const base::Closure& end_of_segment_cb,
                                     const LogCB& log_cb) {
  DVLOG(1) << __FUNCTION__;
  DCHECK_EQ(state_, UNINITIALIZED);
  init_cb_ = init_cb;
  config_cb_ = config_cb;
  new_buffers_cb_ = new_buffers_cb;
  new_segment_cb_ = new_segment_cb;
  end_of_segment_cb_ = end_of_segment_cb;
  log_cb_ = log_cb;

  ChangeState(INITIALIZED);
}

void MPEGAudioStreamParserBase::Flush() {
  DVLOG(1) << __FUNCTION__;
  DCHECK_NE(state_, UNINITIALIZED);
  queue_.Reset();
  timestamp_helper_->SetBaseTimestamp(base::TimeDelta());
  in_media_segment_ = false;
}

bool MPEGAudioStreamParserBase::Parse(const uint8* buf, int size) {
  DVLOG(1) << __FUNCTION__ << "(" << size << ")";
  DCHECK(buf);
  DCHECK_GT(size, 0);
  DCHECK_NE(state_, UNINITIALIZED);

  if (state_ == PARSE_ERROR)
    return false;

  DCHECK_EQ(state_, INITIALIZED);

  queue_.Push(buf, size);

  bool end_of_segment = true;
  BufferQueue buffers;
  for (;;) {
    const uint8* data;
    int data_size;
    queue_.Peek(&data, &data_size);

    if (data_size < 4)
      break;

    uint32 start_code = data[0] << 24 | data[1] << 16 | data[2] << 8 | data[3];
    int bytes_read = 0;
    bool parsed_metadata = true;
    if ((start_code & start_code_mask_) == start_code_mask_) {
      bytes_read = ParseFrame(data, data_size, &buffers);

      // Only allow the current segment to end if a full frame has been parsed.
      end_of_segment = bytes_read > 0;
      parsed_metadata = false;
    } else if (start_code == kICYStartCode) {
      bytes_read = ParseIcecastHeader(data, data_size);
    } else if ((start_code & kID3StartCodeMask) == kID3v1StartCode) {
      bytes_read = ParseID3v1(data, data_size);
    } else if ((start_code & kID3StartCodeMask) == kID3v2StartCode) {
      bytes_read = ParseID3v2(data, data_size);
    } else {
      bytes_read = FindNextValidStartCode(data, data_size);

      if (bytes_read > 0) {
        DVLOG(1) << "Unexpected start code 0x" << std::hex << start_code;
        DVLOG(1) << "SKIPPING " << bytes_read << " bytes of garbage.";
      }
    }

    CHECK_LE(bytes_read, data_size);

    if (bytes_read < 0) {
      ChangeState(PARSE_ERROR);
      return false;
    } else if (bytes_read == 0) {
      // Need more data.
      break;
    }

    // Send pending buffers if we have encountered metadata.
    if (parsed_metadata && !buffers.empty() && !SendBuffers(&buffers, true))
      return false;

    queue_.Pop(bytes_read);
    end_of_segment = true;
  }

  if (buffers.empty())
    return true;

  // Send buffers collected in this append that haven't been sent yet.
  return SendBuffers(&buffers, end_of_segment);
}

void MPEGAudioStreamParserBase::ChangeState(State state) {
  DVLOG(1) << __FUNCTION__ << "() : " << state_ << " -> " << state;
  state_ = state;
}

int MPEGAudioStreamParserBase::ParseFrame(const uint8* data,
                                          int size,
                                          BufferQueue* buffers) {
  DVLOG(2) << __FUNCTION__ << "(" << size << ")";

  int sample_rate;
  ChannelLayout channel_layout;
  int frame_size;
  int sample_count;
  int bytes_read = ParseFrameHeader(
      data, size, &frame_size, &sample_rate, &channel_layout, &sample_count);

  if (bytes_read <= 0)
    return bytes_read;

  // Make sure data contains the entire frame.
  if (size < frame_size)
    return 0;

  DVLOG(2) << " sample_rate " << sample_rate
           << " channel_layout " << channel_layout
           << " frame_size " << frame_size
           << " sample_count " << sample_count;

  if (config_.IsValidConfig() &&
      (config_.samples_per_second() != sample_rate ||
       config_.channel_layout() != channel_layout)) {
    // Clear config data so that a config change is initiated.
    config_ = AudioDecoderConfig();

    // Send all buffers associated with the previous config.
    if (!buffers->empty() && !SendBuffers(buffers, true))
      return -1;
  }

  if (!config_.IsValidConfig()) {
    config_.Initialize(audio_codec_, kSampleFormatF32, channel_layout,
                       sample_rate, NULL, 0, false, false,
                       base::TimeDelta(), base::TimeDelta());

    base::TimeDelta base_timestamp;
    if (timestamp_helper_)
      base_timestamp = timestamp_helper_->GetTimestamp();

    timestamp_helper_.reset(new AudioTimestampHelper(sample_rate));
    timestamp_helper_->SetBaseTimestamp(base_timestamp);

    VideoDecoderConfig video_config;
    bool success = config_cb_.Run(config_, video_config, TextTrackConfigMap());

    if (!init_cb_.is_null())
      base::ResetAndReturn(&init_cb_).Run(success, kInfiniteDuration(), true);

    if (!success)
      return -1;
  }

  // TODO(wolenetz/acolwell): Validate and use a common cross-parser TrackId
  // type and allow multiple audio tracks, if applicable. See
  // https://crbug.com/341581.
  scoped_refptr<StreamParserBuffer> buffer =
      StreamParserBuffer::CopyFrom(data, frame_size, true,
                                   DemuxerStream::AUDIO, 0);
  buffer->set_timestamp(timestamp_helper_->GetTimestamp());
  buffer->set_duration(timestamp_helper_->GetFrameDuration(sample_count));
  buffers->push_back(buffer);

  timestamp_helper_->AddFrames(sample_count);

  return frame_size;
}

int MPEGAudioStreamParserBase::ParseIcecastHeader(const uint8* data, int size) {
  DVLOG(1) << __FUNCTION__ << "(" << size << ")";

  if (size < 4)
    return 0;

  if (memcmp("ICY ", data, 4))
    return -1;

  int locate_size = std::min(size, kMaxIcecastHeaderSize);
  int offset = LocateEndOfHeaders(data, locate_size, 4);
  if (offset < 0) {
    if (locate_size == kMaxIcecastHeaderSize) {
      MEDIA_LOG(log_cb_) << "Icecast header is too large.";
      return -1;
    }

    return 0;
  }

  return offset;
}

int MPEGAudioStreamParserBase::ParseID3v1(const uint8* data, int size) {
  DVLOG(1) << __FUNCTION__ << "(" << size << ")";

  if (size < kID3v1Size)
    return 0;

  // TODO(acolwell): Add code to actually validate ID3v1 data and
  // expose it as a metadata text track.
  return !memcmp(data, "TAG+", 4) ? kID3v1ExtendedSize : kID3v1Size;
}

int MPEGAudioStreamParserBase::ParseID3v2(const uint8* data, int size) {
  DVLOG(1) << __FUNCTION__ << "(" << size << ")";

  if (size < 10)
    return 0;

  BitReader reader(data, size);
  int32 id;
  int version;
  uint8 flags;
  int32 id3_size;

  if (!reader.ReadBits(24, &id) ||
      !reader.ReadBits(16, &version) ||
      !reader.ReadBits(8, &flags) ||
      !ParseSyncSafeInt(&reader, &id3_size)) {
    return -1;
  }

  int32 actual_tag_size = 10 + id3_size;

  // Increment size if 'Footer present' flag is set.
  if (flags & 0x10)
    actual_tag_size += 10;

  // Make sure we have the entire tag.
  if (size < actual_tag_size)
    return 0;

  // TODO(acolwell): Add code to actually validate ID3v2 data and
  // expose it as a metadata text track.
  return actual_tag_size;
}

bool MPEGAudioStreamParserBase::ParseSyncSafeInt(BitReader* reader,
                                                 int32* value) {
  *value = 0;
  for (int i = 0; i < 4; ++i) {
    uint8 tmp;
    if (!reader->ReadBits(1, &tmp) || tmp != 0) {
      MEDIA_LOG(log_cb_) << "ID3 syncsafe integer byte MSb is not 0!";
      return false;
    }

    if (!reader->ReadBits(7, &tmp))
      return false;

    *value <<= 7;
    *value += tmp;
  }

  return true;
}

int MPEGAudioStreamParserBase::FindNextValidStartCode(const uint8* data,
                                                      int size) const {
  const uint8* start = data;
  const uint8* end = data + size;

  while (start < end) {
    int bytes_left = end - start;
    const uint8* candidate_start_code =
        static_cast<const uint8*>(memchr(start, 0xff, bytes_left));

    if (!candidate_start_code)
      return 0;

    bool parse_header_failed = false;
    const uint8* sync = candidate_start_code;
    // Try to find 3 valid frames in a row. 3 was selected to decrease
    // the probability of false positives.
    for (int i = 0; i < 3; ++i) {
      int sync_size = end - sync;
      int frame_size;
      int sync_bytes = ParseFrameHeader(
          sync, sync_size, &frame_size, NULL, NULL, NULL);

      if (sync_bytes == 0)
        return 0;

      if (sync_bytes > 0) {
        DCHECK_LT(sync_bytes, sync_size);

        // Skip over this frame so we can check the next one.
        sync += frame_size;

        // Make sure the next frame starts inside the buffer.
        if (sync >= end)
          return 0;
      } else {
        DVLOG(1) << "ParseFrameHeader() " << i << " failed @" << (sync - data);
        parse_header_failed = true;
        break;
      }
    }

    if (parse_header_failed) {
      // One of the frame header parses failed so |candidate_start_code|
      // did not point to the start of a real frame. Move |start| forward
      // so we can find the next candidate.
      start = candidate_start_code + 1;
      continue;
    }

    return candidate_start_code - data;
  }

  return 0;
}

bool MPEGAudioStreamParserBase::SendBuffers(BufferQueue* buffers,
                                            bool end_of_segment) {
  DCHECK(!buffers->empty());

  if (!in_media_segment_) {
    in_media_segment_ = true;
    new_segment_cb_.Run();
  }

  BufferQueue empty_video_buffers;
  TextBufferQueueMap empty_text_map;
  if (!new_buffers_cb_.Run(*buffers, empty_video_buffers, empty_text_map))
    return false;
  buffers->clear();

  if (end_of_segment) {
    in_media_segment_ = false;
    end_of_segment_cb_.Run();
  }

  timestamp_helper_->SetBaseTimestamp(base::TimeDelta());
  return true;
}

}  // namespace media