media/formats/mp4/es_descriptor.cc

   1 // Copyright 2014 The Chromium Authors. All rights reserved.
   2 // Use of this source code is governed by a BSD-style license that can be
   3 // found in the LICENSE file.
   4
   5 #include "media/formats/mp4/es_descriptor.h"
   6
   7 #include "media/base/bit_reader.h"
   8 #include "media/formats/mp4/rcheck.h"
   9
  10 // The elementary stream size is specific by up to 4 bytes.
  11 // The MSB of a byte indicates if there are more bytes for the size.
  12 static bool ReadESSize(media::BitReader* reader, uint32* size) {
  13   uint8 msb;
  14   uint8 byte;
  15
  16   *size = 0;
  17
  18   for (size_t i = 0; i < 4; ++i) {
  19     RCHECK(reader->ReadBits(1, &msb));
  20     RCHECK(reader->ReadBits(7, &byte));
  21     *size = (*size << 7) + byte;
  22
  23     if (msb == 0)
  24       break;
  25   }
  26
  27   return true;
  28 }
  29
  30 namespace media {
  31
  32 namespace mp4 {
  33
  34 // static
  35 bool ESDescriptor::IsAAC(uint8 object_type) {
  36   return object_type == kISO_14496_3 || object_type == kISO_13818_7_AAC_LC;
  37 }
  38
  39 ESDescriptor::ESDescriptor()
  40     : object_type_(kForbidden) {
  41 }
  42
  43 ESDescriptor::~ESDescriptor() {}
  44
  45 bool ESDescriptor::Parse(const std::vector<uint8>& data) {
  46   BitReader reader(&data[0], data.size());
  47   uint8 tag;
  48   uint32 size;
  49   uint8 stream_dependency_flag;
  50   uint8 url_flag;
  51   uint8 ocr_stream_flag;
  52   uint16 dummy;
  53
  54   RCHECK(reader.ReadBits(8, &tag));
  55   RCHECK(tag == kESDescrTag);
  56   RCHECK(ReadESSize(&reader, &size));
  57
  58   RCHECK(reader.ReadBits(16, &dummy));  // ES_ID
  59   RCHECK(reader.ReadBits(1, &stream_dependency_flag));
  60   RCHECK(reader.ReadBits(1, &url_flag));
  61   RCHECK(!url_flag);  // We don't support url flag
  62   RCHECK(reader.ReadBits(1, &ocr_stream_flag));
  63   RCHECK(reader.ReadBits(5, &dummy));  // streamPriority
  64
  65   if (stream_dependency_flag)
  66     RCHECK(reader.ReadBits(16, &dummy));  // dependsOn_ES_ID
  67   if (ocr_stream_flag)
  68     RCHECK(reader.ReadBits(16, &dummy));  // OCR_ES_Id
  69
  70   RCHECK(ParseDecoderConfigDescriptor(&reader));
  71
  72   return true;
  73 }
  74
  75 uint8 ESDescriptor::object_type() const {
  76   return object_type_;
  77 }
  78
  79 const std::vector<uint8>& ESDescriptor::decoder_specific_info() const {
  80   return decoder_specific_info_;
  81 }
  82
  83 bool ESDescriptor::ParseDecoderConfigDescriptor(BitReader* reader) {
  84   uint8 tag;
  85   uint32 size;
  86   uint64 dummy;
  87
  88   RCHECK(reader->ReadBits(8, &tag));
  89   RCHECK(tag == kDecoderConfigDescrTag);
  90   RCHECK(ReadESSize(reader, &size));
  91
  92   RCHECK(reader->ReadBits(8, &object_type_));
  93   RCHECK(reader->ReadBits(64, &dummy));
  94   RCHECK(reader->ReadBits(32, &dummy));
  95   RCHECK(ParseDecoderSpecificInfo(reader));
  96
  97   return true;
  98 }
  99
 100 bool ESDescriptor::ParseDecoderSpecificInfo(BitReader* reader) {
 101   uint8 tag;
 102   uint32 size;
 103
 104   RCHECK(reader->ReadBits(8, &tag));
 105   RCHECK(tag == kDecoderSpecificInfoTag);
 106   RCHECK(ReadESSize(reader, &size));
 107
 108   decoder_specific_info_.resize(size);
 109   for (uint32 i = 0; i < size; ++i)
 110     RCHECK(reader->ReadBits(8, &decoder_specific_info_[i]));
 111
 112   return true;
 113 }
 114
 115 }  // namespace mp4
 116
 117 }  // namespace media