Problem with encoding

[leavittx]

I've made a simple encoding app, with code very similar to api2-decode-encode-video.cpp.
The only difference is that I don't really need an output Stream, since I want to manually operate on encoded packets.
The first problem that I see is that there is no VideoEncoderContext constructor which doesn't require a Stream parameter (I mean there is, but it will lead to problems, no such example provided). So maybe there should be a constructor for such scenario, shouldn't it?

Even when I create a fake output Stream, avcodec_receive_frame (codeccontext.cpp, int decode(AVCodecContext *avctx, AVFrame *picture, int *got_picture_ptr, const AVPacket *avpkt), returns AVERROR(EAGAIN) during roughly first 50 decode() calls, although I seem to provide correct input data to it.

I assume it should return valid packet every time a new frame is provided to avcodec_send_packet, shouldn't it? Any ideas on that?

Libavcodec version 57.80.100, target platform Windows 10 64-bit (visual studio toolchain is used)

[h4tr3d]

Uh... browser drop my anwer. In short: not an issue, just a WAD.

Some codecs has Delay in some amount of frames. Delay - major thing. In some cases Delay requires by performance optimization or by codec design itself (B-frames).

So, in some cases you should put some amount of packets to the codec before receive first decoded frame. Count of packets that sends to codec before first frame is a codec Delay. As a result, avcodec_receive_frame() can produce EAGAIN error for a some time.

Also, after input stream finished you must put some amount null packets to drain codecs and receive leftover frames. You should do it until EAGAIN (in my API: I do not put null packet to the codec, so it does not moves to flush state, basically it is an error) or AVERROR_EOF.

For more details see:

• https://www.ffmpeg.org/doxygen/3.1/group__lavc__encdec.html
• https://blogs.gentoo.org/lu_zero/2016/03/29/new-avcodec-api/