On 04/08/17 14:06, Jorge Ramirez wrote: > On 08/04/2017 01:51 PM, Mark Thompson wrote: >>> + if (ret) >>> + return 0; >>> + >>> + return avpriv_v4l_dequeue(cap_pool, frame, NULL, timeout); >>> +} >> What happens to the decoder if some parameters like resolution change >> mid-stream? (Try the stream h264/reinit-large_420_8-to-small_420_8.h264 in >> the fate samples.) > > yes, it breaks - the player still shows and image but it is corrupted. > I am not sure how to handle this situation to be honest...so need to look > into this.
There should be some way to detect it from the decoder, I think? (I don't actually know how this works in V4L2.) To compare, if you look at MMAL (perhaps the most similar API in current lavc) there is a special FORMAT_CHANGED return when dequeuing a frame, and the decoder is reconfigured with new buffers when that happens: <http://git.videolan.org/?p=ffmpeg.git;a=blob;f=libavcodec/mmaldec.c;h=0b1195dc3e6f09beb74e3e47404456114596c499;hb=HEAD#l713>. >> >> Also, are the frames returned here actually still used by the decoder >> internally as reference frames, or is the reference frame copied somewhere >> else? > > I think once the buffers are dequeued, the v4l2 decoder doesnt keep any > references to it. >> (Seems slightly unlikely that they would be copied given the additional >> memory requirements, but I know discrete desktop GPUs (which admittedly have >> 9001x the memory bandwidth and power budget) do do this to hide the possible >> issues.) I think, though I'm not entirely sure because I haven't run it, >> that the returned buffers will only have the user reference, so will appear >> to be writable to following filters - if that ends up writing on reference >> frames then the decoder will break. > > ack Ok. I'm a bit surprised because of the performance implications of writing everything twice, but if we don't have to think about it at all then whatever. - Mark _______________________________________________ ffmpeg-devel mailing list ffmpeg-devel@ffmpeg.org http://ffmpeg.org/mailman/listinfo/ffmpeg-devel
