mpeg4-generic parsing for AAC over RFC3640

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文章來源:http://my-tech-knowledge.blogspot.com/2008/02/aac-parsing-over-rfc3640.html

Preface

Reference

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

AU-header structure


AAC frame in AU-header


!!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.

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