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

Michael IV explomaster at gmail.com
Mon Jul 31 11:00:19 EEST 2017

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:


But, because my YUV format is not 420P, but NV12 I am trying to force it on
AVCodecContext when initializing it with this line:

        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?
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