[Libav-user] mjr to opus audio conversion - corrupted results

[Mateusz Koslacz]

Hi,

In our project we use janus-gateway (http://janus.conf.meetecho.com/) as a
webRTC gateway and also as a stream recorder. We are on the tests stage of
our project, and after very long development time we have ecountered a bug
that is a blocker for whole project. After real tests of recording streams
using janus we realized that audio and video are out of sync in recordings,
despite of fact, that live they are perfectly in sync.

Janus records two *.mjr files for each recording - one for video, and one
for audio. Janus also provides own converter to convert this files to
*.webm for video and *.opus for audio. After that, we use ffmpeg to merge
this files. By recording stopwatch view on the stream we concluded, that
video has correct length and speed, so most probably this is something
wrong with audio recording or converting.

Firstly, janus was using libogg for converting *.mjr audio to *.opus.
Regarding described issues author decided to switch to libav audio
processing. You can check how it's done in this file
https://github.com/meetecho/janus-gateway/blob/pprec-opus-libav/postprocessing/pp-opus.c
starting
from 90 line.

Returned data is a lil bit smaller than data obtained using libogg:

-rw-r--r-- 1 mateusz mateusz  17987445 lip  8 11:58
> rec-2215547545-audio-nolibogg.opus
> -rw-r--r-- 1 mateusz mateusz 221841174 lip  8 11:56
> rec-2215547545-video.webm
> -rw-r--r-- 1 mateusz mateusz  18074102 lip  8 11:52
> rec-2215547545-audio-libogg.opus


Unfortunately, returned data is somehow corrupted - ffprobe results for
libav processing output:

[ogg @ 0x4336540] Codec not found
> rec-2215547545-audio-nolibogg.opus: End of file


and for compare, for libogg version:

Input #0, ogg, from 'rec-2215547545-audio-libogg.opus':
>   Duration: 01:20:32.98, start: 0.000000, bitrate: 29 kb/s
>     Stream #0:0: Audio: opus, 48000 Hz, stereo, fltp


Moreover, no player can play this file - VLC just does nothing, and
Rythmbox says "Can't play file: {null}".


Is this because of improper use of libav api, or maybe it is some libav
bug? How could we possibly overcome this problems?

For more details you can read our whole conversation with janus author here:
https://groups.google.com/forum/#!topic/meetecho-janus/lMCtBm7VbMY


Regards,

Mateusz Koślacz
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