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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.

• Correctly Allocate And Fill Frame In FFmpeg

  14 avril 2022, par Michel Feinstein

  I am filling a Frame with a BGR image for encoding, and I am getting a memory leak. I think I got to the source of the problem but it appears to be a library issue instead. Since FFmpeg is such a mature library, I think I am misusing it and I would like to be instructed on how to do it correctly.

  



  I am allocating a Frame using :

  



  AVFrame *bgrFrame = av_frame_alloc();


  



  And later I allocate the image in the Frame using :

  



  av_image_alloc(bgrFrame->data, bgrFrame->linesize, bgrFrame->width, bgrFrame->height, AV_PIX_FMT_BGR24, 32);


  



  Then I fill the image allocated using :

  



  av_image_fill_pointers(bgrFrame->data, AV_PIX_FMT_BGR24, bgrFrame->height, originalBGRImage.data, bgrFrame->linesize);


  



  Where originalBGRImage is an OpenCV Mat.

  



  And this has a memory leak, apparently, av_image_alloc() allocates memory, and av_image_fill_pointers() also allocates memory, on the same pointers (I can see bgrFrame->data[0] changing between calls).

  



  If I call

  



  av_freep(&bgrFrame->data[0]);


  



  After av_image_alloc(), it's fine, but if I call it after av_image_fill_pointers(), the program crashes, even though bgrFrame->data[0] is not NULL, which I find very curious.

  



  Looking FFmpeg's av_image_alloc() source code, I see it calls av_image_fill_pointers() twice inside it, once allocating a buffer buff....and later in av_image_fill_pointers() source code, data[0] is substituted by the image pointer, which is (I think) the source of the memory leak, since data[0] was holding buf from the previous av_image_alloc() call.

  



  So this brings the final question : What's the correct way of filling a frame with an image ?.

  


• Correctly Allocate And Fill Frame In FFmpeg

  24 février 2016, par mFeinstein

  I am filling a Frame with a BGR image for encoding, and I am getting a memory leak. I think I got to the source of the problem but it appears to be a library issue instead. Since FFmpeg is such a mature library, I think I am misusing it and I would like to be instructed on how to do it correctly.

  I am allocating a Frame using :

  AVFrame *bgrFrame = av_frame_alloc();

  And later I allocate the image in the Frame using :

  av_image_alloc(bgrFrame->data, bgrFrame->linesize, bgrFrame->width, bgrFrame->height, AV_PIX_FMT_BGR24, 32);

  Then I fill the image allocated using :

  av_image_fill_pointers(bgrFrame->data, AV_PIX_FMT_BGR24, bgrFrame->height, originalBGRImage.data, bgrFrame->linesize);

  Where originalBGRImage is an OpenCV Mat.

  And this has a memory leak, apparently, av_image_alloc() allocates memory, and av_image_fill_pointers() also allocates memory, on the same pointers (I can see bgrFrame->data[0] changing between calls).

  If I call

  av_freep(&bgrFrame->data[0]);

  After av_image_alloc(), it’s fine, but if I call it after av_image_fill_pointers(), the program crashes, even though bgrFrame->data[0] is not NULL, which I find very curious.

  Looking FFmpeg’s av_image_alloc() source code, I see it calls av_image_fill_pointers() twice inside it, once allocating a buffer buff....and later in av_image_fill_pointers() source code, data[0] is substituted by the image pointer, which is (I think) the source of the memory leak, since data[0] was holding buf from the previous av_image_alloc() call.

  So this brings the final question : What’s the correct way of filling a frame with an image ?.