Re: [LAU] skipping chunks of video with ffmpeg2theora and icecast, DVinput

From: Robin Gareus <robin@email-addr-hidden>
Date: Fri May 20 2011 - 16:07:41 EEST

On 05/20/2011 02:35 PM, Peder Hedlund wrote:
> Quoting Luka Prin?i? // Nova deViator <nova@email-addr-hidden>:
>
>>
>> hi,
>>
>> i have been doing videostreaming now number of times and somehow i
>> always run into the same peculiar problem.
>>
>> whenever there is more action on camera, especially zoomins and a lot
>> of audio (like bass and distorted vocals for example), the stream starts
>> to continously skip chunks of video stream of about 0.5-1 second,
>> every 0.5-1 second.
>
> The obvious guess would be that your CPU is too slow and can't keep up
> with recoding the video stream.
> The other guess is that the camera and/or the interface can't push that
> amount of data in real time to the PC.

Hi Luka,

The problem is likely the former (the DV input is a bitstream with
constant bps and usually no problem): Panning and zooming puts
addidtional some strain on the encoder (motion compensation calc) and
also produces bandwidth spikes.

AT LAC, we were able to kick out some remote-participants with quick
camera panning due to bandwith spikes so we tried to avoid those :) BTW,
we were able to max-out CPU a 2.8GHz quad-core with two ffmpeg2theora
instances.

You can check if decreasing the quality (`-v 3`) helps and give
`--speedlevel 2` a try: it uses less CPU, for increased output bandwidth.

Down-scaling the video decreases CPU usage of the encoder, but requires
a few CPU cycles to perform the scaling, in particular if scaling to non
multiples of 16: try `-x 384 -y 288 -aspect 4:3` instead of
` -x 393 -y 288` (it /should/ not make a difference since Theora
requires the geometry to be multiples of 8 (or 16?), but ffmpeg2theora
may just be scaling/cropping/expanding twice?!).

HTH,
robin
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Received on Fri May 20 16:15:02 2011

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