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• FFMpeg C++ How to create a filter with multiple outputs ?

  11 septembre 2020, par GoodSimon

  For example, we have one AVFrame with a size of 128x128 pixels and the task is to split the AVFrame into 4 parts (4 separate AVFrame). To do this, I fill the graph with filters using the avfilter_graph_parse2(...) function, and then call avfilter_graph_config(...).

  


  Let's start. Let's cut out the top left corner. To crop a frame, we need to use the crop filter, which means we initialize the AVFilterGraph graph with the line :

  


  buffer = width = 128: height = 128: pix_fmt = 2: time_base = 1/25, pixel_aspect = 128/64 [pad_in];
[pad_in] crop = w = 64: h = 64: x = 0: y = 0, buffersink;


  


  Everything works great ! Now let's try to make several outputs :

  


  buffer = width = 128: height = 128: pix_fmt = 2: time_base = 1/25, pixel_aspect = 128/64 [pad_in];
[pad_in] crop = w = 64: h = 64: x = 0: y = 0, buffersink;
[pad_in] crop = w = 64: h = 64: x = 64: y = 0, buffersink;
[pad_in] crop = w = 64: h = 64: x = 0: y = 64, buffersink;
[pad_in] crop = w = 64: h = 64: x = 64: y = 64, buffersink


  


  As you can see, we have one buffer for the input image, 4 crop filters for cutting each piece, and 4 buffersink filters for the output images. The call avfilter_graph_parse2(...) returns 0, which is good, but avfilter_graph_config() returns the error code -22 == AVERROR(EINVAL) and the message is output to the console : Input pad "default" with type video of the filter instance "Parsed_crop_3" of crop not connected to any source.

  


  I am asking for your help in creating a filter with multiple outputs.

  


• FFmpeg encoding through h264_qsv : pts < dts

  29 décembre 2023, par Mario

  I'm modifying a portion of code that encodes input frames in an output mp4 file via the h264 software encoder which works quite well. Most of the code comes from https://ffmpeg.org/doxygen/6.0/mux_8c-example.html.

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  I changed the "working" code to use the h264_qsv hardware accelerated encoder. After a lot of work the new code produces h264 encoded frames. For testing purpose I can write them with

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  fwrite(pkt->data, pkt->size, 1, fout)

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  and mpv displays frames correctly (with some warnings).

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  When I use regular :

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  av_interleaved_write_frame(fmt_ctx, pkt)

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  (as from previously working code) returns an error and on stderr :

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  [mp4 @ 0x7f82a80b3b40] pts (-1574122160956548608) < dts&#xA;(1574122160956547584) in stream 0

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  To look for the cause I added the following lines just before av_interleaved_write_frame(). I read that it may be a non-fatal error and so I continue after the errors, but there isn't output.

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  frame->pts=210
  &#xA;pkt->pts=-1574122160956548608
  &#xA;pkt->dts=1574122160956547584
  &#xA;[mp4 @ 0x7effb40b3b40] pts (-1574122160956548608) < dts (1574122160956547584) in stream 0
  &#xA;...
  &#xA;frame->pts=240
  &#xA;pkt->pts=-1574122160956548608
  &#xA;pkt->dts=1574122160956548096
  &#xA;[mp4 @ 0x7effb40b3b40] pts (-1574122160956548608) < dts (1574122160956548096) in stream 0

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  I did another test assigning incremental values to pkt->pts and pkt->dts, it works but resulting fps is wrong, and I don't think it is the right solution !

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  Why does the av_interleaved_write_frame(fmt_ctx, pkt) function returns an error with h264_qsv encoder ? Who should set pkt->pts and pkt->dts ?

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• rtsp timeout av_read_frame

  30 novembre 2012, par user1175197

  I am using ffmpeg to play an RTSP stream. I have a loop like

      while (av_read_frame(formatContext, packet)>=0)
  
      {
  
        doWork();
  
      }

  I can watch the stream as long as there is something moving in front of the camera. But whenever the view is stable the above function returns EOF as I checked with av_strerror. Any ideas why and how to fix it ?

  thanks