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• avcodec_encode_video2 crash on MinGW32 (but not on MinGW64)

  27 février 2018, par ksb496

  I have been testing for years a software that I am developing, compiled only for 64-bit systems through Qt-MinGW64, without experiencing any kind of issue regarding video encoding (which is one of the features of such application). Recently, I have been attempting to build the corresponding x86 version of my software by compiling it with Qt-MingGW32.

  However, after bulding the same ffmpeg and x264 library versions to create the 32-bit versions and successfully linking them to my project, the application keeps crashing after few frames are encoded, due to segmentation fault error. This is very strange because, as I indicated before, it works flawlessly when compiled for 64-bit systems.

  I have also lost a considerable amount hours trying to combine a big amount of different versions of both ffmpeg and x264 libraries, but with no luck either. Neither it works when disabling threads both for x264 and ffmpeg libraries, hence it does not seem to be a win32 threading issue. Therefore, I have concluded that the error is most likely in my code, which by some chance beyond my comprehension tells ffmpeg to allocate the right amount of memory in the x64 version, but not in the x86 version.

  It must be pointed out also that before the avcodec_encode_video2 call, I do the following calls, among others, in order to allocate the memory associated to the corresponding items (AVFrame, AVCodec, etc.), such as

  avcodec_open2( my_codec_context, my_codec, &opt );
  
  my_av_frame=av_frame_alloc();

  More precisely, the details involving the code structure that I am using can be found here.

  Therefore, the error appears to be more subtle than just issues regarding uninitialized memory.

  Many thanks in advance.

  UPDATE :

  I have discovered the focus of the problem. For some reason, FFmpeg/x264 libraries behave abnormally in Win32 GUI applications compiled with Qt-MinGW32, while they run correctly in Win32 console applications, also compiled with Qt-WinGW32. I have proven this claim performing two dummy tests, in which the exact same piece of code is run through a console application and on a GUI application, succeeding in the first case and failing in the latter one. The code for such tests can be found below, along with the x264 and FFmpeg libraries used in my projects, together with instructions to build them in msys2 with MinGW32 :

  https://takeafile.com/?f=hisusinivi

  I have no idea whether it can be solved by simply tweaking the code or it is a serious bug involving an incompatibility issue. If it is the latter, should it be reported to the Qt/FFmpeg/x264 staff as a major bug ?

• avcodec_encode_video2 crash on MinGW32 (but not on MinGW64)

  27 février 2018, par ksb496

  I have been testing for years a software that I am developing, compiled only for 64-bit systems through Qt-MinGW64, without experiencing any kind of issue regarding video encoding (which is one of the features of such application). Recently, I have been attempting to build the corresponding x86 version of my software by compiling it with Qt-MingGW32.

  However, after bulding the same ffmpeg and x264 library versions to create the 32-bit versions and successfully linking them to my project, the application keeps crashing after few frames are encoded, due to segmentation fault error. This is very strange because, as I indicated before, it works flawlessly when compiled for 64-bit systems.

  I have also lost a considerable amount hours trying to combine a big amount of different versions of both ffmpeg and x264 libraries, but with no luck either. Neither it works when disabling threads both for x264 and ffmpeg libraries, hence it does not seem to be a win32 threading issue. Therefore, I have concluded that the error is most likely in my code, which by some chance beyond my comprehension tells ffmpeg to allocate the right amount of memory in the x64 version, but not in the x86 version.

  It must be pointed out also that before the avcodec_encode_video2 call, I do the following calls, among others, in order to allocate the memory associated to the corresponding items (AVFrame, AVCodec, etc.), such as

  avcodec_open2( my_codec_context, my_codec, &opt );
  
  my_av_frame=av_frame_alloc();

  More precisely, the details involving the code structure that I am using can be found here.

  Therefore, the error appears to be more subtle than just issues regarding uninitialized memory.

  Many thanks in advance.

  UPDATE :

  I have discovered the focus of the problem. For some reason, FFmpeg/x264 libraries behave abnormally in Win32 GUI applications compiled with Qt-MinGW32, while they run correctly in Win32 console applications, also compiled with Qt-WinGW32. I have proven this claim performing two dummy tests, in which the exact same piece of code is run through a console application and on a GUI application, succeeding in the first case and failing in the latter one. The code for such tests can be found below, along with the x264 and FFmpeg libraries used in my projects, together with instructions to build them in msys2 with MinGW32 :

  https://takeafile.com/?f=hisusinivi

  I have no idea whether it can be solved by simply tweaking the code or it is a serious bug involving an incompatibility issue. If it is the latter, should it be reported to the Qt/FFmpeg/x264 staff as a major bug ?

• Why does ffmpeg return a different framecount than ffprobe for the same file ?

  5 mars 2018, par Greg

  I’m trying to count the number of frames in a video but ffmpeg and ffprobe are giving me two different answers.

  $ time ffprobe -v error -count_frames -select_streams v:0 -show_entries stream=nb_read_frames -of default=nokey=1:noprint_wrappers=1 myvideo.mp4
  
  2858
  
  
  
  real    0m2.987s
  
  user    0m2.740s
  
  sys     0m0.172s

  When I check the same file with ffmpeg I get 2 more frames...

  $ time ffmpeg -y -i myvideo.mp4 -vcodec copy -acodec copy -f null /dev/null 2>&1 | grep 'frame=' | awk '{print $2}'
  
  2860
  
  
  
  real    0m0.127s
  
  user    0m0.080s
  
  sys     0m0.032s

  I used ffprobe to output all of the frames and count the number of "[FRAME]"s in the resultant output...

  ffprobe -i myvideo.mp4 -show_frames -v error | grep -o '\[FRAME\]' | wc -l
  
  2858

  Which as you can see shows the number ffprobe thought there were.

  Obviously I would prefer to use ffmpeg here because it is significantly faster than ffprobe and I am dealing with thousands of videos that need parsing and indexing. However the failure isn’t consistent across multiple videos ; sometimes it’s 1 out, other times it’s 2 or more...

  Unfortunately, I have been counting frames for the past two years using the ffmpeg method, so I have a significant library of videos to reprocess now ... he gulps... I guess its a good way to verify the readability of the files on the cluster... even so, its going to take probably a few weeks to recalculate all of the existing video frame sizes.