On Thu, 2010-09-16 at 20:11 +0400, Kulti wrote: > On Thu, Sep 16, 2010 at 5:34 PM, Tomas Härdin <[email protected]>wrote: > > > Please don't top post on this list. It makes it harder for people to > > read it. > > > > On Thu, 2010-09-16 at 17:02 +0400, Kulti wrote: > > > Hm... Thanks, I'm use flv-container, but how to set VFR? It's mean, that > > I > > > need to modify AVCodecContext.time_base before encoding every frames? > > > > > > On Thu, Sep 16, 2010 at 4:43 PM, Tomas Härdin <[email protected] > > >wrote: > > > > > > > On Thu, 2010-09-16 at 13:36 +0400, Kulti wrote: > > > > > Hi, all. > > > > > > > > > > I have a webcam and need to transcode mjpeg to any formats, but > > sometime > > > > > webcam lagged and fps fall down. Can ffmpeg atuo fill dropped frames > > to > > > > > constantly fps? > > > > > > > > Why do you want constant fps? Just use a container that handles VFR > > > > (avi, flv, mov etc.). > > > > > > > > Anyway, assuming the frames are timestamped correctly ffmpeg should > > > > behave correctly. If not, try forcing constant framerate with -r. > > > > > > > > /Tomas > > > > > > > > FLV has a fixed time base of 1 kHz, so it's always VFR. In other cases, > > like AVI, you can set time_base to be less than or equal to the inverse > > of the maximum fps. > > > > In other words, if you know your camera can't deliver more than 50 fps > > you can set time_base to 1/50, 1/123, 1/10000 or whatever. In the > > specific case of AVI you shouldn't set it too low though, since it pads > > with empty packets for the "missing" time stamps (IIRC something like > > 39*16 = 624 B overhead if you mux 25 fps with a time base of 1 kHz). FLV > > does not have this problem though. > > > > Hope that helps :) > > > > /Tomas > > > > _______________________________________________ > > libav-user mailing list > > [email protected] > > https://lists.mplayerhq.hu/mailman/listinfo/libav-user > > > > > Sorry for top-post... and thanks for your help. > > So, I set time_base to fixed value 1/25 (that I get from AVCodecContext for > mjpeg-decoder). Then I added timer and frame-counter before > av_write_frame(). I see, that fps is 19-21. But I need live-streaming. So, I > hardcoded time_base to 1/20, and all works fine before webcam is not lag, > but after fall down fps to 15 transcoding process broken. > > Yes, I understand, that must be working for transcoding into file, but I > need real-time transoding for live streaming. I can't see any way instead > inserting frames, when some drops...
What you do is convert the current time to the stream's time base, and stick that value in as the packet's DTS. Sort of like this: //remember what the time was when the program started int64_t t0 = get_microseconds_time(); //replace with whatever function is suitable ... //for each AVPacket int64_t t = get_microseconds_time(); pkt->dts = av_rescale_q(t - t0, AV_TIME_BASE_Q, st->time_base); av_write_frame(...); That seconds line converts your zero-centered times from microseconds to the stream's time base. This means if the camera suddenly slows down a bit, the DTS value will have gaps. This is fine as long as the muxer can handle VFR (such as AVI and FLV). /Tomas
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