Could be. With JPEG, if you wanted to go crazy, you could perhaps decompress each macroblock on a separate thread...
On Tue, Feb 10, 2015 at 9:46 AM, Renaud BOBIN <[email protected]> wrote: > That’s is why on MJPEG there is no latency ? > > Frame N doesn’t depend on N-1 nor N+1 so each thread is independent ? > > > > > > *De :* [email protected] [mailto:[email protected]] > *De la part de* Robin Stevens > *Envoyé :* mardi 10 février 2015 10:33 > *À :* This list is about using libavcodec, libavformat, libavutil, > libavdevice and libavfilter. > *Objet :* Re: [Libav-user] Real time camera IP RTSP H264 > > > > > > On Tuesday, February 10, 2015, Maziar Mehrabi <[email protected]> > wrote: > > Hi, > > I wonder why multithreading causes latency. > > My understanding is that having concurrent threads should improve > performance. > > Is there any explanation for this? > > Thanks, > > > > > > Without any knowledge of the code in question: concurrency can increase > overall throughput (for particular kinds of task) but increased latency is > a common payoff. > > > > Imagine each thread as a separate decoder with carefully controlled access > to some common data/state. To fully decode the Nth frame probably requires > at least a partial decode (possibly a complete decode) of the N-1 frame. > Therefore although the decoding for the Nth frame may happen on a separate > processor core, it's likely not truly independent of the other cores. > > > > So if you have 4 threads, T4 is waiting on T3, which is waiting on T2 and > on T1. Even though T1 may have finished frame 1, it probably can't fully > decode frame 5 until 4 is available from T4... > > > > But that's just my guess! > > > ------------------------------ > <http://www.avast.com/> > > Ce courrier électronique ne contient aucun virus ou logiciel malveillant > parce que la protection Antivirus avast! <http://www.avast.com/> est > active. > > > _______________________________________________ > Libav-user mailing list > [email protected] > http://ffmpeg.org/mailman/listinfo/libav-user > >
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