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• How to fill/calculate motion_val in FFMPEG ?

  10 février 2015, par MenuItem42

  I’m trying to get motion vectors of a mpeg video via ffmpeg (in c++).
  The problem that I have is, that motion_val along with motion_subsample_log2 and mb_type of the AVFrame class remain empty and/or aren’t initialized (debugger says 0x0) and it seems that they are only available because of compatibility reasons
  I’ve read in the ffmpeg wiki, that you can debug the motion vectors of the video via command line with

  ffmpeg -vismv pf -i input.mp4 output.mp4

  The result is that the output.mp4 has motion vector arrows. So I searched for the –vismv parameter in the code and found in libavcodec\options.c a long list of options :

  {"vismv", "visualize motion vectors (MVs)", OFFSET(debug_mv), FF_OPT_TYPE_INT, DEFAULT, 0, INT_MAX, V|D, "debug_mv"},   

  I suppose that this line affects somehow debug_mv of AVCodecContext. With this assumption I searched for further information and I found some code snippets which I thought might help.

  pAVCodecContext->debug_mv =  FF_DEBUG_VIS_MV_P_FOR | FF_DEBUG_VIS_MV_B_FOR | FF_DEBUG_MB_TYPE | FF_DEBUG_MV;

  and

  pAVCodecContext->debug |= FF_DEBUG_MV;    

  But both didn’t trigger the calculation or filling of the motion_val array.
  By the way my code is based on the code by Victor Hsieh and Jiasi Chen and this code is basically the ffmpeg sourcecode (libavcodec\mpegvideo.c). I also tried to find (also with help of the documentation) the piece of code that triggers the calculation, but because of the complexity of the code I didn’t get any results.
  The question is now, if is there any possibility to fill this variables or start the calculation of the motion vector table or is there any other alternative way to get the motion vectors of every block of the mpeg-frames.

  Edit :

  I forgot to mention my ffmpeg version

  Zeranoe’s FFmpeg version : 2014-07-08 git-14e2406

  • libavutil 52. 91.100 / 52. 91.100
  • libavcodec 55. 68.102 / 55. 68.102
  • libavformat 55. 45.100 / 55. 45.100
  • libavdevice 55. 13.101 / 55. 13.101
  • libavfilter 4. 10.100 / 4. 10.100
  • libswscale 2. 6.100 / 2. 6.100
  • libswresample 0. 19.100 / 0. 19.100
  • libpostproc 52. 3.100 / 52. 3.100

  Changed to a newer version (2.5), but it didn’t change/solve the problem.

• how can I let ffmpeg use cuda context created externally ?

  20 février 2020, par Wang

  Some libraries for example the ffmpeg are using dynamically loaded one. But our project is linked to cuda driver directly. I would like to share the same context between them. I tried the naive way to do this :

  1. initialize and create cuda context via ffmpeg’s av_hwdevice_ctx_create.
  2. then use cuCtxSetCurrent to set the obtained the context created by step one.

  This works fine. However, I want share the context in the other way around : create and manage the context in our code then share the context with ffmpeg. Is this possible ?

• avutil/fifo : Fix the case where func() returns less bytes than requested in av_fifo_g...

  14 juillet 2015, par Zhang Rui

  avutil/fifo : Fix the case where func() returns less bytes than requested in av_fifo_generic_write()
  Signed-off-by : Michael Niedermayer <michael@niedermayer.cc>
  

  • [DH] libavutil/fifo.c