[Libav-user] Problem using avcodec_decode_video2 for reading HEVC stream

Krishna krish.rao.v at gmail.com
Thu Aug 28 22:42:50 CEST 2014

Thanks Markus and wm4. I gave your suggestion a shot and this is what I
did. In my situation, I call the decoder() and expect a frame. However, the
decoder will buffer several packets right in the beginning. Since I need a
single frame per call, I now keep track of the number of times it read
packets without decoding (in the beginning). I call this "numInitPackets".

In the end I flush out that many packets using a null packet. And it
worked! Thank you so much for your help!
ah thank you. didnt know that one. but makes sense yes.

> On 27 aug. 2014, at 23:37, wm4 <nfxjfg at googlemail.com> wrote:
> On Wed, 27 Aug 2014 19:14:36 +0200
> Markus Pfundstein <markuspfundstein86 at gmail.com> wrote:
>> a frame can consist of several packets. thats why you need to call
av_decode_video2 multiple times until it has a fully decoded frame for you.
the return values tell you how much data was read.
>> you should adjust packet.data and packet.size by those values.
>> there a a lot of examples out there that show this.
> In libavcodec/libavformat, a packet consists of exactly one frame (and
> libavformat goes out of its way to guarantee this). But decoding can
> incur a delay of several frames. That means, at start of decoding you
> have to feed the decoder several packets without getting a video frame
> back, and at end of decoding you need to feed it null packets to get
> the remaining frames.
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