Have to say, this issue has been a long grievance of mine. There is no reason to delay frames when the decoder is set up to ignore B frames as there is no reordering to be done; ideally this should be zero-delay case (packet goes in, frame goes out) yet the most common decoders delay frames anyway, as if to decode B frames. Moreover, with the "new" send/receive API I think there is no reason to delay frames at all - a single send_packet could decode and queue multiple frames to be received, so it makes sense to send frames as soon as possible - yet that is not the case as well.
пт, 24 мая 2024 г. в 13:17, Andreas Rheinhardt <andreas.rheinha...@outlook.com>: > > Michael Henrik Bodenhoff via ffmpeg-devel: > > Hi , > > > > my team recently had to abandon switching to using FFmpeg from specific > > decoder implementations (NvDEC, Intel Media SDK , IPP and quite a few codec > > specific decoders) because of big performance issues because of the way > > FFmpeg works….. or at least we think it is (we’re FFmpeg noobs 😃 ) > > > > It's actually an issue we also had with Intel Media SDK, leading us to pay > > Intel to extend Media SDK to do what we needed. > > > > Our product is a video surveillance system, and that means we have to > > decode a LOT of video streams simultaneously. > > > > For motion detection we want to only decode keyframes, and skip P and B > > frames , and that works fine with FFmpeg most of the time, except for when > > the video stream contains B frames. > > Without B-Frames it’s really simple (simplified pseudocode) : > > > > while(true) > > { > > receiveStreamCompleteFrame(); > > If(KeyFrame) > > { > > avcodec_send_packet(); > > if(avcodec_receive_frame()==0) > > { > > // do motion detection > > } > > } > > } > > > > But! with B Frames FFmpeg doesn’t return keyframes when they are decoded, > > they are kept, and we can’t seem to flush them out. avcodec_flush_buffers > > allow us to continue to next keyframe, but it doesn’t seem to give us the > > keyframe we just gave to FFmpeg with avcodec_send_packet. > > > > while(true) > > { > > receiveStreamCompleteFrame(); > > If(KeyFrame) > > { > > avcodec_send_packet(); > > if(avcodec_receive_frame()==0) > > { > > // do motion detection > > } > > Else > > { > > avcodec_flush_buffers(); > > if(avcodec_receive_frame()==0) > > { > > // do motion detection > > } > > } > > } > > } > > > > Calling avcodec_receive_frame after calling avcodec_flush_buffer results in > > -11 and no frame > > > > is there anyway around this ? And if not, could FFmpeg be made to have this > > functionality ? > > > > I tried contacting one of the FFmpeg consultants from > > https://ffmpeg.org/consulting.html but never got a response > > > > Send your packet with the keyframe, send a NULL packet (to signal EOF), > then the internally stored frames should be output by > avcodec_receive_frame(). Then flush the decoder (to be able to send new > packets to it). > > - Andreas > > _______________________________________________ > ffmpeg-devel mailing list > ffmpeg-devel@ffmpeg.org > https://ffmpeg.org/mailman/listinfo/ffmpeg-devel > > To unsubscribe, visit link above, or email > ffmpeg-devel-requ...@ffmpeg.org with subject "unsubscribe". _______________________________________________ ffmpeg-devel mailing list ffmpeg-devel@ffmpeg.org https://ffmpeg.org/mailman/listinfo/ffmpeg-devel To unsubscribe, visit link above, or email ffmpeg-devel-requ...@ffmpeg.org with subject "unsubscribe".