[Libav-user] Decoding h264 (NV12) stream from NVENC

[Michael IV]

So you basically say that the decoder 'knows' to detect interleaved UV in
NV12 UV plane and decode it correctly to yuv420p without any hints from the
application?
Then why my YUV frame is corrupted? How can I detect where is the problem?
I also found this SO answer regarding h264 streaming from NVENC.
https://stackoverflow.com/questions/33185966/how-to-stream-h-264-video-over-udp-using-the-nvidia-nvenc-hardware-encoder

And I currently don't set those params for encoder.Do I have to?


On Mon, Jul 31, 2017 at 11:04 AM, Hendrik Leppkes <h.leppkes at gmail.com>
wrote:

> On Mon, Jul 31, 2017 at 10:00 AM, Michael IV <explomaster at gmail.com>
> wrote:
> > Hi! I am using NVENC encoder to create h264 stream.The YUV format is
> NV12.
> > Now, I need also to decode that stream back to YUV.I wrote a module for
> > that,based on
> > this example:
> >
> > https://gist.github.com/roxlu/9329339
> >
> > But, because my YUV format is not 420P, but NV12 I am trying to force it
> on
> > AVCodecContext when initializing it with this line:
> >
> >         avcodec_register_all();
> >         mCodec = avcodec_find_decoder(AV_CODEC_ID_H264);
> >         mCodecContext = avcodec_alloc_context3(mCodec);
> >         mCodecContext->pix_fmt = AVPixelFormat::AV_PIX_FMT_NV12;
> >
> >
> > But when I am receiving the decoded AVFrame, I see that the
> AVFrame->format
> > property is
> > set to zero, which is enum for 420P. Also inspecting the planes and other
> > props of this struct I see that the decoder tried to decode it as 420P.
> (3
> > planes , 3 line sizes etc.) .And of course,when trying to play the
> output of
> > such a YUV frame , there is just a green screen.
> > I am trying to understand where is my error.Is there some data that
> decoder
> > misses from the h264 stream and it doesn't allow it to guess the pixel
> > format?Or maybe I need to set pixel format for the codec context in a
> some
> > different way?
> >
>
> You can't control the output pixel format of the H264 decoder. A video
> is not encoded as "NV12", its encoded as 4:2:0 YUV, NV12 is just one
> representation of this format.
> As such, our decoder will always decode 4:2:0 YUV content to yuv420p,
> not nv12. If you require NV12 in your application, you can convert
> from yuv420p to nv12 using swscale (a lossless conversion).
>
> - Hendrik
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