[FFmpeg-devel] [Jack-Devel] [PATCH] libavdevice: JACK demuxer

Olivier Guilyardi list
Fri Feb 27 20:31:01 CET 2009

J?rn Nettingsmeier wrote:
> Olivier Guilyardi wrote:
>> Hi Jack and FFmpeg developers,
>> below is a patch against ffmpeg svn r17646 for using JACK as an audio input
>> device in ffmpeg, as in:
>> ffmpeg -f jack -ac 2 -i ffmpeg out.wav
>> This connects to JACK with two input ports: ffmpeg:input_1 and ffmpeg:input_2.
>> You still need to connect these ports using jack_connect or qjackctl.
>> This demuxer is already being used in pre-production for teaching lessons
>> broadcasting, using a DV camera, several mics and icecast.
>> A downloadable version is available here:
>> http://www.samalyse.com/code/misc/patches/ffmpeg-r17646-jack-0.3.diff
> lovely. can you give some more info about your usage scenario? are you
> broadcasting live as well?
> is there any chance to use this solution for a live broadcast toolchain with
> dvgrab (no audio) | ffmpeg2theora -f jack (audio comes via soundcard) |
> oggfwd

This is precisely what we are doing :) Except that we're using ffmpeg directly
to produce theora (with the libtheora encoder), because ffmpeg2theora doesn't
support several inputs.

In regard to the current scenario, the audio is recorded using several mics, one
on the desk, another at the back of the classroom, etc.., a bit as in a concert.
Then, this is all mixed through jack, merged with video in ffmpeg, and
broadcasted on the web with icecast.

We are currently using dvgrab, and the A/V sync is good. But it requires playing
with the buffer sizes at various places. It should be easier/better to directly
use the ffmpeg dv input devices (dv1394 or libdc1394), but we can't do that
because our camera is not IIDC compliant.


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