[asterisk-bugs] [Asterisk 0010741]: [patch] AMR NB pass-through

[noreply at bugs.digium.com]

A NOTE has been added to this issue. 
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http://bugs.digium.com/view.php?id=10741 
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Reported By:                klaus3000
Assigned To:                
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Project:                    Asterisk
Issue ID:                   10741
Category:                   Core-General
Reproducibility:            always
Severity:                   minor
Priority:                   normal
Status:                     new
Asterisk Version:            SVN 
SVN Branch (only for SVN checkouts, not tarball releases):  trunk 
SVN Revision (number only!): 82546 
Disclaimer on File?:        N/A 
Request Review:              
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Date Submitted:             09-17-2007 08:30 CDT
Last Modified:              09-17-2007 16:27 CDT
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Summary:                    [patch] AMR NB pass-through
Description: 
This adds pass-through of AMR narrow band to Asterisk's core, chan_sip and
rtp.

Further, a format_amrnb.c was added which should store in RFC conform AMR
files.
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---------------------------------------------------------------------- 
 klaus3000 - 09-17-07 16:27  
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This is a pass-through patch - thus transcoding is not support. We also
have a working AMR codec for Asterisk
http://sip.fontventa.com/trac/asterisk/browser/amr but:
1. Including a codec would require paying license fees
2. The code is GPL and not disclaimed

These are the main reasons that I have submitted a pass through patch to
avoid the legal issus (pretty the same as G.729).

Recording: I tried Record(myfile.amr,10) but it did not worked. It tried
to convert to slinear. Maybe it was due to the silence option (which is
mandatory according to the documentation). I will try again tomorrow.

SDP options: The mode set is not only requested withthe SDP, but also with
the CMR (codec mode request) byte in the RTP packet (the first byte of the
payload).   Why not just forward the mode-set too (if the SDP was not
already sent back)?

Nevertheless I would prefer starting with AMR pass through with all the
SDP options support and add them when we encounter problems.

It think the octed-aligned mode option is more important to handle then
the mode-set. Currently the patch only handles octed-aligned mode. This is
also what is used by rtsp streaming servers and 3gp files. Thus, we used
the RTP octed-aligned format in ast_frames. To support other modes too (and
for reencdoing) we would either need a second frame format or
ast_frame->subsubtype.

Conclusion: This is pass-through patch and thus can not handle transcoding
issues (just like g729 or video pass through) 

Issue History 
Date Modified   Username       Field                    Change               
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09-17-07 16:27  klaus3000      Note Added: 0070703                          
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