[Libav-user] FFMPEG decoding H264 and Multithreading

Jérôme SALAYET jerome.salayet at hymatom.fr
Fri Feb 8 18:49:46 CET 2013

Hello, I'm using FFMPEG to decode video streaming from an IP Camera. all seems good but I try to decrease the CPU usage of my application when I decompress several differents streams.
In fact, I have a dual core processor, and if I decode one stream, my CPU usage is very low (so good). If I decompress two streams, it's ok too. But if I had a third decompression, my CPU increase from 2-5% to 25-30%.

So, I try to activate Mutlithreading in FFMPEG (compiling with --enable-w32threads) with Mingw.

But if I initialize my AVCodecContext with thread_count=3 (because I have a dual core processor) and thread_type = FF_THREAD_FRAME|FF_THREAD_SLICE, when I use avcodec_open2, I always got an result error -22: The maximum value for lowres supported by the decoder is 0. I read where this message appear in FFMPEG code source and it's in utils.c

if (avctx->codec->max_lowres < avctx->lowres || avctx->lowres < 0)

But in my code before call avcodec_open2( lpCodecCtx, lpCodec, ...) I have m_lpCodec->max_lowres=0 and m_lpCodecCtx->lowres=0, so I don't understa,nd why I always have this error.

After add some traces in Utils.c, it seems I have avctx->codec->max_lowres=0 and avctx->lowres=3 but I don't understand why...

Perhaps, trying Multithreading isn"t the good solution to decrease the CPU usage, I'm not very sure of this point.

Thanks for your answers,


Ingénieur Informatique
Tél :    04 67 87 61 12
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Site web : www.hymatom.fr <http://www.hymatom.fr/> 
Email : jerome.salayet at hymatom.fr <mailto:jerome.salayet at hymatom.fr> 


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