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
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