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      1 // Copyright (c) 2012 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/mp4/es_descriptor.h"
      6 
      7 #include "media/base/bit_reader.h"
      8 #include "media/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
    118