[Libav-user] need help in ffmpeg

[Васькевич Руслан]

this is code for decoding h264 stream from camera using ffmpeg. But I want
to use hardware acceleration for decoding video. I Can not find good
sample. There are a lot of question about this topic but there is no answer

    string url = @"rtsp://admin:123456@192.168.0.201:554";

        FFmpegInvoke.av_register_all();
        FFmpegInvoke.avcodec_register_all();
        FFmpegInvoke.avformat_network_init();


        AVFormatContext* pFormatContext = FFmpegInvoke.avformat_alloc_context();
        if (FFmpegInvoke.avformat_open_input(&pFormatContext, url,
null, null) != 0)
            throw new Exception("Could not open file");

        if (FFmpegInvoke.avformat_find_stream_info(pFormatContext, null) != 0)
            throw new Exception("Could not find stream info");

        AVStream* pStream = null;
        for (int i = 0; i < pFormatContext->nb_streams; i++)
        {
            if (pFormatContext->streams[i]->codec->codec_type ==
AVMediaType.AVMEDIA_TYPE_VIDEO)
            {
                pStream = pFormatContext->streams[i];
                break;
            }
        }
        if (pStream == null)
            throw new Exception("Could not found video stream");

        AVCodecContext codecContext = *(pStream->codec);
        int width = codecContext.width;
        int height = codecContext.height;
        AVPixelFormat sourcePixFmt = codecContext.pix_fmt;
        AVCodecID codecId = codecContext.codec_id;
        var convertToPixFmt = AVPixelFormat.PIX_FMT_BGR24;
        SwsContext* pConvertContext =
FFmpegInvoke.sws_getContext(width, height, sourcePixFmt,

width, height, convertToPixFmt,

FFmpegInvoke.SWS_FAST_BILINEAR, null, null, null);
        if (pConvertContext == null)
            throw new Exception("Could not initialize the conversion context");

        var pConvertedFrame = (AVPicture*)FFmpegInvoke.avcodec_alloc_frame();
        int convertedFrameBufferSize =
FFmpegInvoke.avpicture_get_size(convertToPixFmt, width, height);
        var pConvertedFrameBuffer =
(byte*)FFmpegInvoke.av_malloc((uint) convertedFrameBufferSize);
        FFmpegInvoke.avpicture_fill(pConvertedFrame,
pConvertedFrameBuffer, convertToPixFmt, width, height);

        AVCodec* pCodec = FFmpegInvoke.avcodec_find_decoder(codecId);
        if (pCodec == null)
            throw new Exception("Unsupported codec");

        // Reusing codec context from stream info,
        // as an alternative way it could look like this: (but it
works not for all kind of codecs)
        // AVCodecContext* pCodecContext =
FFmpegInvoke.avcodec_alloc_context3(pCodec);
        AVCodecContext* pCodecContext = &codecContext;

        if ((pCodec->capabilities & FFmpegInvoke.CODEC_CAP_TRUNCATED)
== FFmpegInvoke.CODEC_CAP_TRUNCATED)
            pCodecContext->flags |= FFmpegInvoke.CODEC_FLAG_TRUNCATED;

        if (FFmpegInvoke.avcodec_open2(pCodecContext, pCodec, null) < 0)
            throw new Exception("Could not open codec");

        AVFrame* pDecodedFrame = FFmpegInvoke.avcodec_alloc_frame();

        var packet = new AVPacket();
        AVPacket* pPacket = &packet;
        FFmpegInvoke.av_init_packet(pPacket);

        int frameNumber = 0;
        while (true)
        {
            Console.WriteLine("frame: {0}", frameNumber);

            if (FFmpegInvoke.av_read_frame(pFormatContext, pPacket) < 0)
                throw new Exception("Could not read frame");

            if (pPacket->stream_index != pStream->index)
                continue;

            int gotPicture = 0;
            int size =
FFmpegInvoke.avcodec_decode_video2(pCodecContext, pDecodedFrame,
&gotPicture, pPacket);
            if (size < 0)
                throw new Exception(string.Format("Error while
decoding frame {0}", frameNumber));

            if (gotPicture == 1)
            {
                byte** src = &pDecodedFrame->data_0;
                byte** dst = &pConvertedFrame->data_0;
                FFmpegInvoke.sws_scale(pConvertContext, src,
pDecodedFrame->linesize, 0,
                                        height, dst, pConvertedFrame->linesize);

                byte* convertedFrameAddress = pConvertedFrame->data_0;

                var imageBufferPtr = new IntPtr(convertedFrameAddress);

                using (var bitmap = new Bitmap(width, height,
pConvertedFrame->linesize[0], PixelFormat.Format24bppRgb,
imageBufferPtr))
                {
                    bitmap.Save(@"frame.buffer.jpg", ImageFormat.Jpeg);
                }
            }
            //frameNumber++;
        }

        FFmpegInvoke.av_free(pConvertedFrame);
        FFmpegInvoke.av_free(pConvertedFrameBuffer);
        FFmpegInvoke.sws_freeContext(pConvertContext);

        FFmpegInvoke.av_free(pDecodedFrame);
        FFmpegInvoke.avcodec_close(pCodecContext);
        FFmpegInvoke.avformat_close_input(&pFormatContext);

How use hardware acceleration for decoding stream(hwaccel)?
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