Technical Knowledge: mpeg4-generic parsing for AAC over RFC3640【转载】

mpeg4-generic parsing for AAC over RFC3640

Preface

Reference
  • RFC3640
  • ISO/IEC 14496-3
  • ISO/IEC 13818-7, MPEG-2 Advanced Coding (AAC)

AU-header structure

[au-header.png]

AAC frame in AU-header

[rfc3640-aac.png]

!!NOTES:
1) DVB-H supports High bit-rate AAC while streaming

2) The AU-headers are configured using MIME format parameters
may be empty. Don’t know how to know it according to SDP description??
(if anyone knows the answer, please let me know..:P)
3) If AAC frames are carried over RFC3640, ADTS header is needed for each AAC frame

for AAC decoder using the following info.

++++++++++++++++++++++++++
| ADTS header (length may vary) |
++++++++++++++++++++++++++
| AAC frame (length may vary) |

++++++++++++++++++++++++++

Example:
[ADTS header]
Please refer to adts_frame() of ISO/IEC 13818-7
[SDP info]
a=rtpmap:97 mpeg4-generic/32000/1
a=fmtp:97 streamType=5;profile-level-id=41;mode=AAC-hbr;sizelength=13;indexlength=3;indexdeltalength=3;config=1288

=> clock-rate = 32000

=> “config” should be parsed based on AudioSpecificConfig() in ISO/IEC 14496-3,

and when forming a ADTS header for an AAC frame,

sampling_frequency_index, channel_configuration needs to be

extracted from “config” field and

frame_length is calculated from RTP payload when parsing AU-header.

来源: Technical Knowledge: mpeg4-generic parsing for AAC over RFC3640

发表评论

电子邮件地址不会被公开。 必填项已用*标注