[Libav-user] "no picture" from decoding single h264 keyframe

cyril poulet xenosender at gmail.com
Thu Apr 3 10:11:26 CEST 2014

are you sure that the packet contains the entire frame ?
You might just miss some data, try decoding the next packets until you get
a picture decoded...

2014-04-03 3:28 GMT+02:00 Andrey Utkin <andrey.krieger.utkin at gmail.com>:

> Hi all!
> I am checking a C application using ffmpeg libs, which does the following:
> it demuxes h264 stream from RTSP channel, and, when an event happens,
> it waits for next keyframe (determined with AVPacket.flags &
> AV_PKT_FLAG_KEY), creates appropriate decoder AVCodecContext for it,
> and decodes the frame for further processing. The idea is that having
> a keyframe, we can decode just single encoded frame and get valid
> picture. This approach must have been working correctly in practice,
> but now i have it not working with h264 stream from IP camera Axis
> M1034-W; the decoding operation indicates that we got no picture (by a
> avcodec_decode_video2() flag parameter), and prints
> [h264 @ blah] no picture
> This shouldn't be RTP loss, the camera is connected directly to my PC
> with a patchcord.
> If that is needed, i can share a remuxed stream dump.
> BTW Is there an easy way to print out the types of encoded h264 frames
> (I, P, B...)?
> Could please somebody elaborate what exactly happens? Is above
> approach generally broken, or it can be fixed (without decoding a lot
> more frames)?
> --
> Andrey Utkin
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> Libav-user at ffmpeg.org
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