I think "*For video, the packet contains exactly one frame.*" is not true for all codecs, but is for most of the usual ones. try this one : http://blog.tomaka17.com/2012/03/libavcodeclibavformat-tutorial/ It may be that avcodec_decode_video2 recognizes that the first packet data is header and discards it as irrelevant for image decoding...
2014-07-22 17:14 GMT+02:00 Matt Orlando <[email protected]>: > The documentation > <https://www.ffmpeg.org/doxygen/trunk/group__lavf__decoding.html#ga4fdb3084415a82e3810de6ee60e46a61> > says > "*For video, the packet contains exactly one frame.*" I used this > <http://dranger.com/ffmpeg/> tutorial to understand the flow of what > needs to be done. Some of the calls were deprecated so a few google > searches got me the replacements. What appears to be happening is those > lost frames are just gone...the data isn't being accumulated. Is it > possible my av_free_packet call is in a bad spot? > > > On Tue, Jul 22, 2014 at 10:58 AM, cyril poulet < > [email protected]> wrote: > >> what av_read_frame does is take some data and fill your packet with it. >> There is no guaranty that a full frame is in the packet, or even image data. >> avcodec_decode_video2 is the only way to know if you have decoded an >> image : you feed it your successive packets, it accumulates data, and tells >> you when the data allowed him to successfully decode an image (through >> frameFinished) >> You should look online for basic examples of how to decode safely vids, >> there is in particular a tutorial which introduces the structure SafePacket >> (first version has been updated for latest versions of the libs) >> >> >> 2014-07-22 16:49 GMT+02:00 Matt Orlando <[email protected]>: >> >> Thanks for the response. That's very interesting, though I wonder if it >>> could actually be header related. Based on the videos, I know for sure >>> there are exactly 64 frames in the first movie, for instance. My >>> m_FrameRead is only increased if avcodec_decode_video2 says it was able to >>> get a picture. My thinking is that if it was a header that was read, that >>> function wouldn't set frameFinished to "true". So av_read_frame hits the >>> EOF when my m_FrameRead counter is only 56. >>> >>> Are you saying that perhaps the av_read_frame is reading a bunch of data >>> (header + frames) and my avcodec_decode_video2 says there's no picture >>> because there's header data in there. Then a few frames later (or maybe >>> next frame), av_read_frame reads more data, now including the 9th 'frame' >>> and finally avcodec_decode_video2 decodes and I increment my counter (which >>> would be now 1 when I'd want it to be 9). >>> >>> Thanks for the help! >>> -Matt >>> >>> >>> On Tue, Jul 22, 2014 at 8:30 AM, cyril poulet < >>> [email protected]> wrote: >>> >>>> according to the doc, av_read_packet does not check wether the data in >>>> the decoded frame is a valid image or not. >>>> As it is always the 8 first "frames" missing, I would assume it is the >>>> header that gets decoded first. >>>> Have you noticed missing images when comparing the first real decoded >>>> image and your stream in a player ? >>>> >>>> >>>> 2014-07-21 18:37 GMT+02:00 Matt Orlando <[email protected]>: >>>> >>>>> Hi folks, >>>>> >>>>> I'm having some trouble with the decoding of my h.264 movies. I've >>>>> tested with different videos, one 64 frames long and another 52 frames >>>>> long. In both cases, the first 8 frames (exactly 8) weren't decoding. In >>>>> other words, the call to avcodec_decode_video2 returns 0 for the >>>>> got_picture variable. I track the frames read and received for our system >>>>> and I never get notice that all the frames were read because my counter >>>>> doesn't increase for the first 8...however all of the subsequent calls to >>>>> av_read_frame return EOF. To prevent any confusion (or perhaps just to >>>>> add >>>>> some context), I need the raw data from each decoded frame since I don't >>>>> treat them as a frame to a movie but rather a frame of x,y,z positional >>>>> data. >>>>> >>>>> I work in Unity but made a plugin to communicate with the libraries to >>>>> read and decode the h.264 movies. This is our update function: >>>>> >>>>> bool H264Stream::Update(int desiredFrame) >>>>> { >>>>> if( desiredFrame <= m_FrameRead ) >>>>> return true; >>>>> >>>>> int frameFinished = 0; >>>>> >>>>> if( av_read_frame( m_AVFormat, &m_Packet ) >= 0 ) >>>>> { >>>>> if( m_Packet.stream_index == m_AVStream->index ) >>>>> { >>>>> av_frame_unref( m_AVFrame ); >>>>> avcodec_decode_video2( m_AVContext, m_AVFrame, >>>>> &frameFinished, &m_Packet ); >>>>> >>>>> if( frameFinished != 0 ) >>>>> { >>>>> sws_scale( m_SwsContext, m_AVFrame->data, >>>>> m_AVFrame->linesize, 0, m_AVContext->height, m_Picture->data, >>>>> m_Picture->linesize ); >>>>> >>>>> m_FrameRead++; >>>>> >>>>> av_free_packet( &m_Packet ); >>>>> } >>>>> } >>>>> } >>>>> >>>>> return m_FrameRead >= desiredFrame; >>>>> } >>>>> >>>>> >>>>> Oh, quick note, this is my first time using these libraries so if >>>>> there's something blatantly wrong with how I'm doing this, please let me >>>>> know. :) Just keep in mind, it's the full frame of 'raw' data I use >>>>> (post-decode) that I pass back into my Unity c# scripts. >>>>> >>>>> Thanks for the help everyone! >>>>> -Matt >>>>> >>>>> _______________________________________________ >>>>> Libav-user mailing list >>>>> [email protected] >>>>> http://ffmpeg.org/mailman/listinfo/libav-user >>>>> >>>>> >>>> >>>> _______________________________________________ >>>> Libav-user mailing list >>>> [email protected] >>>> http://ffmpeg.org/mailman/listinfo/libav-user >>>> >>>> >>> >>> _______________________________________________ >>> Libav-user mailing list >>> [email protected] >>> http://ffmpeg.org/mailman/listinfo/libav-user >>> >>> >> >> _______________________________________________ >> Libav-user mailing list >> [email protected] >> http://ffmpeg.org/mailman/listinfo/libav-user >> >> > > _______________________________________________ > Libav-user mailing list > [email protected] > http://ffmpeg.org/mailman/listinfo/libav-user > >
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