[Libav-user] Output video data to file and pipe: concurrently

[Yurii Monakov]

You are misusing "ret" variable inside the loop. This loop should drain
frames from decoder, so "ret" should
be assigned from avcodec_receive_frame, not av_interleaved_write_frame
(which works with another context).

Yurii

пт, 1 апр. 2022 г. в 06:40, Hillel Rosensweig via Libav-user <
libav-user at ffmpeg.org>:

> On Thursday, March 31, 2022, 10:39:47 PM GMT+3, Yurii Monakov <
> monakov.y at gmail.com> wrote:
>
>
> Hi
>
> Sorry for some kind of offtopic on this list, but you should try to create
> simple gstreamer pipeline. From my opinion, gstreamer has all pipeline
> elements which you need (tee, decode, encode, whatever) and will be much
> more simpler to get working than bare ffmpeg libraries. You can test your
> pipeline with gst-launch utility.
>
> Yurii
>
> чт, 31 марта 2022 г. в 10:30, Hillel Rosensweig via Libav-user <
> libav-user at ffmpeg.org>:
>
> Hello all,
>
> I have been trying to output video (from my webcam) simultaneously to both
> a file ('out.mkv') and pipe:
> The file gets filtered frames packets, and the pipe: gets ufiltered
> rawvideo.
> My frame rate is 30 fps. However, I am getting a far lower framerate in my
> file output.
>
> Attached is the while loop which reads packets and writes them to output:
>
> while (1) {
>     av_read_frame(ifmt_ctx, packet);
>     stream_index = packet->stream_index;
>
>     StreamContext *stream = &file_stream_ctx[stream_index];
>
>     av_packet_rescale_ts(packet,
>                          ifmt_ctx->streams[stream_index]->time_base,
>                          stream->dec_ctx->time_base);
>     avcodec_send_packet(stream->dec_ctx, packet);
>
>     while (ret >= 0) {
>         avcodec_receive_frame(stream->dec_ctx, stream->dec_frame);
>
>         stream->dec_frame->pts = stream->dec_frame->best_effort_timestamp;
>         ret = filter_encode_write_frame(stream->dec_frame, stream_index,
> file_stream_ctx,
>                                                 file_filter_ctx,
> file_ofmt_ctx);
>         ret = av_interleaved_write_frame(pipe_ofmt_ctx, packet);
>     }
> }
>
> 'ifmt_ctx' is the AVFormatContext for the webcam.
> 'file_ofmt_ctx', is the AVFormatContext for the pipe for the output file,
> and pipe_ofmt_ctx is the AVFormatContext.
> 'file_stream_ctx' and 'file_filter_ctx' are the stream and filter contexts
> used for filtering and encoding the file output.
>
>
> My guess is that writing to the pipe is taking too long and not allowing
> the next packet to be read on time - causing a lower frame rate. Does that
> make sense? If so - any suggestions on how to fix it? (I tried using
> AVFMT_FLAG_NONBLOCK but it doesn't seem to help).
>
> Thanks
>
> Hillel
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> That may be, but for the time being I need to work with ffmpeg libraries
> directly. Any help with my current diretion would be appreciated.
>
> Hillel
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