Desynchronization issue with FLV stream

[elesouef]

Hi,

My goal is to stream from a bt878 acquisition card.

For testing purpose, I streamed really great a XVID file without desynchronization at all with the following command-line :

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--sout '#transcode{vcodec=FLV1,acodec=mp3,vb=2000,samplerate=44100,ab=96}:standard{access=http,mux=ffmpeg{mux=flv},dst=server.fqdn:8080/stream.flv}' --sout-keep

Now, I would like to stream from a bt878 card with the following command-line :

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cvlc -I dummy $VLC_DEV --sout '#transcode{vcodec=FLV1,acodec=mp3,vb=1000,samplerate=44100,ab=96,scale=0.5,vfilter={croppadd{cropbottom=10,cropleft=10,cropright=10}}}:standard{access=http,mux=ffmpeg{mux=flv},dst=server.fqdn:8080/stream.flv}' --sout-keep

with $VLC_DEV :

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VLC_DEV="v4l2:// :v4l2-dev='/dev/video0' :input-slave=alsa://hw:1,0 :v4l2-standard=0:v4l2-standard=0 :v4l2-chroma= :v4l2-input=3 :v4l2-audio-input=0 :v4l2-io=0 :v4l2-width=-1 :v4l2-height=-1 :v4l2-aspect-ratio=4\:3 :v4l2-fps=0 :v4l2-caching=1000 :v4l2-tuner=0 :v4l2-tuner-frequency=-1 :v4l2-tuner-audio-mode=0 :no-v4l2-controls-reset :v4l2-brightness=-1 :v4l2-contrast=-1 :v4l2-saturation=-1 :v4l2-hue=-1 :v4l2-black-level=-1 :v4l2-auto-white-balance=-1 :v4l2-do-white-balance=-1 :v4l2-red-balance=-1 :v4l2-blue-balance=-1 :v4l2-gamma=-1 :v4l2-exposure=-1 :v4l2-autogain=-1 :v4l2-gain=-1 :v4l2-hflip=-1 :v4l2-vflip=-1 :v4l2-hcenter=-1 :v4l2-vcenter=-1 :v4l2-audio-volume=-1 :v4l2-audio-balance=-1 :no-v4l2-audio-mute :v4l2-audio-bass=-1 :v4l2-audio-treble=-1 :v4l2-audio-loudness=-1 :v4l2-set-ctrls= :file-caching=300"

After almost half an hour, sound is in advance from 1 second to the image...

Do you know what can cause this ?

Thank you very much for your help.

[Rémi Denis-Courmont]

"Normally", if the desync comes from within VLC, the slowest of the two elementary stream will completely drop out of the mux. In this case, it looks more like you audio hardware is drifting away from system clock Then I have no ideas how to fix it.

[elesouef]

Thanks for replying.

An idea : is it possible, if I enable the rc interface, to tell vlc to "resync" or to "make the audio stream" be N seconds in advance, therefore getting a "false resync" ?

[elesouef]

Ok, did some more tests :

Common basis : VLC 1.1.7 compiled under debian 6.0 with ffmpeg 0.6.1 source tree as PKG_PATH_AVCODEC.

Configuration 1 : Dell Precision T3500 with Asus MyCinema PCTV Acquisition Card. The FLV stream is desynchronized after 2 hours of streaming. Audio is late by 3 seconds.

Configuration 2 : Dell Precision T3500 with Hauppauge Acquisition Card and Motherboard Sound Card as sound acquisition. Almost the same latency.

What can I do to solve this issue ? Any idea would be greatly appreciated.

[Greg]

There are several posts relating to audio sync (or desync )
Eg. This one
viewtopic.php?f=4&t=87254

Follow the threads and sub links in the above link for others. Might save you some time experimenting?
I don't think there is a solution at the moment