For your first question, it seems that some info about the stream (in stream->codec->extradata) needs to be passed on to the avCodecContext, so these three lines do exactly that (but I never used it personnally, so I'm not sure) For your second question, it seems that you did not see that packetToSend.data is a pointer and is not increased but moved,but it also seems that there is a small mistake : when updating packet, offsetInData must be reset to 0 The code is to take in its entirety : - offsetInData is the amount of data in packet already processed by avcodec_decode_video2 : if you look at the beginning of the loop, the structure Packet is only updated when all its data has been processed. However, there is no guaranty that avcodec_decode_video2 will use all data in the Packet. What the whole structure means is : - process data from the packet through a secondary structure packetToSend, return amount of data processed - if the amount of data processed is >= to the amount of data in Packet, update packet - otherwise, copy in packetToSend data not yet processed (at address packet.packet.data + offsetInData and of size packet.packet.size - offsetInData) and process this data Repeat last step until an update of Packet becomes necessary (and reset offsetInData to 0)
The data in packetToSend is thus re-addressed at each step, not increased. 2014-07-22 22:40 GMT+02:00 Matt Orlando <[email protected]>: > So this tutorial looks like it's covering 2 things that I don't do within > my plugin, which is great news since the answer is somewhere within! > Unfortunately, I'm a bit confused with some things from the tutorial. > > > Can anyone explain this to me, and/or perhaps provide a more legible code > example (c++ / c#)? > > // we need to make a copy of videoStream->codec->extradata and give it to the > context > // make sure that this vector exists as long as the avVideoCodec exists > std::vector codecContextExtraData(stream->codec->extradata, > stream->codec->extradata + stream->codec->extradata_size); > avVideoCodec->extradata = reinterpret_cast(codecContextExtraData.data()); > avVideoCodec->extradata_size = codecContextExtraData.size(); > > The other part I don't understand is what he's doing with the offsetInData > variable. I'm almost definitely misunderstanding his usage, but it looks > as though he's increasing packet.packet.Data by this ever-growing > offsetInData. So hypothetically, if he had a 3 hour movie, that > offsetInData would be enormous! How could his packet.packet.Data array be > large enough to shift the pointer by that amount? I also don't understand > why he's only reading (through the reset function of his packet) if that > offsetInData is larger than the packet size. > > Both of these things confuse me...and both of these things I need to > implement. If anyone can explain any/all of this in as much detail as > possible, I'd be forever grateful. I've got a terrible deadline to hit and > I simply need this to work. Thank you sincerely for the help, folks! > > -Matt > > > > On Tue, Jul 22, 2014 at 2:59 PM, Matt Orlando <[email protected]> > wrote: > >> Thank you very much, I'll take some time and look at this tutorial. >> >> >> On Tue, Jul 22, 2014 at 11:22 AM, cyril poulet < >> [email protected]> wrote: >> >>> 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 >>>> >>>> >>> >>> _______________________________________________ >>> 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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