es_descriptor.cc 2.9 KB

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  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. #include "media/formats/mp4/es_descriptor.h"
  5. #include <stddef.h>
  6. #include "media/base/bit_reader.h"
  7. #include "media/formats/mp4/rcheck.h"
  8. // The elementary stream size is specific by up to 4 bytes.
  9. // The MSB of a byte indicates if there are more bytes for the size.
  10. static bool ReadESSize(media::BitReader* reader, uint32_t* size) {
  11. uint8_t msb;
  12. uint8_t byte;
  13. *size = 0;
  14. for (size_t i = 0; i < 4; ++i) {
  15. RCHECK(reader->ReadBits(1, &msb));
  16. RCHECK(reader->ReadBits(7, &byte));
  17. *size = (*size << 7) + byte;
  18. if (msb == 0)
  19. break;
  20. }
  21. return true;
  22. }
  23. namespace media {
  24. namespace mp4 {
  25. // static
  26. bool ESDescriptor::IsAAC(uint8_t object_type) {
  27. return object_type == kISO_14496_3 || object_type == kISO_13818_7_AAC_LC;
  28. }
  29. ESDescriptor::ESDescriptor()
  30. : object_type_(kForbidden) {
  31. }
  32. ESDescriptor::~ESDescriptor() = default;
  33. bool ESDescriptor::Parse(const std::vector<uint8_t>& data) {
  34. BitReader reader(&data[0], data.size());
  35. uint8_t tag;
  36. uint32_t size;
  37. uint8_t stream_dependency_flag;
  38. uint8_t url_flag;
  39. uint8_t ocr_stream_flag;
  40. uint16_t dummy;
  41. RCHECK(reader.ReadBits(8, &tag));
  42. RCHECK(tag == kESDescrTag);
  43. RCHECK(ReadESSize(&reader, &size));
  44. RCHECK(reader.ReadBits(16, &dummy)); // ES_ID
  45. RCHECK(reader.ReadBits(1, &stream_dependency_flag));
  46. RCHECK(reader.ReadBits(1, &url_flag));
  47. RCHECK(!url_flag); // We don't support url flag
  48. RCHECK(reader.ReadBits(1, &ocr_stream_flag));
  49. RCHECK(reader.ReadBits(5, &dummy)); // streamPriority
  50. if (stream_dependency_flag)
  51. RCHECK(reader.ReadBits(16, &dummy)); // dependsOn_ES_ID
  52. if (ocr_stream_flag)
  53. RCHECK(reader.ReadBits(16, &dummy)); // OCR_ES_Id
  54. RCHECK(ParseDecoderConfigDescriptor(&reader));
  55. return true;
  56. }
  57. uint8_t ESDescriptor::object_type() const {
  58. return object_type_;
  59. }
  60. const std::vector<uint8_t>& ESDescriptor::decoder_specific_info() const {
  61. return decoder_specific_info_;
  62. }
  63. bool ESDescriptor::ParseDecoderConfigDescriptor(BitReader* reader) {
  64. uint8_t tag;
  65. uint32_t size;
  66. uint64_t dummy;
  67. RCHECK(reader->ReadBits(8, &tag));
  68. RCHECK(tag == kDecoderConfigDescrTag);
  69. RCHECK(ReadESSize(reader, &size));
  70. RCHECK(reader->ReadBits(8, &object_type_));
  71. RCHECK(reader->ReadBits(64, &dummy));
  72. RCHECK(reader->ReadBits(32, &dummy));
  73. RCHECK(ParseDecoderSpecificInfo(reader));
  74. return true;
  75. }
  76. bool ESDescriptor::ParseDecoderSpecificInfo(BitReader* reader) {
  77. uint8_t tag;
  78. uint32_t size;
  79. RCHECK(reader->ReadBits(8, &tag));
  80. RCHECK(tag == kDecoderSpecificInfoTag);
  81. RCHECK(ReadESSize(reader, &size));
  82. decoder_specific_info_.resize(size);
  83. for (uint32_t i = 0; i < size; ++i)
  84. RCHECK(reader->ReadBits(8, &decoder_specific_info_[i]));
  85. return true;
  86. }
  87. } // namespace mp4
  88. } // namespace media