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• QOpenGLWidget video rendering perfomance in multiple processes

  24 novembre 2018, par MasterAler

  My problem may seem vague without code, but it actually isn’t.

  So, there I’ve got an almost properly-working widget, which renders video frames.

  Qt 5.10 and QOpenGLWidget subclassing worked fine, I didn’t make any sophisticated optimizations — there are two textures and a couple of shaders, converting YUV pixel format to RGB — glTexImage2D() + shaders, no buffers.

  Video frames are obtained from FFMPEG, it shows great performance due to hardware acceleration... when there is only one video window.

  The piece of software is a "video wall" — multiple independent video windows on the same screen. Of course, multi-threading would be the preferred solution, but legacy holds for now, I can’t change it.

  So, 1 window with Full HD video consumes 2% CPU & 8-10% GPU regardless of the size of the window. But 7-10 similar windows, launched from the same executable at the same time consume almost all the CPU. My math says that 2 x 8 != 100...

  My best guesses are :

  • This is a ffmpeg decoder issue, hardware acceleration still is not magic, some hardware pipeline stalls
  • 7-8-9 independent OpenGL contexts cost a lot more than 1 cost x N
  • I’m not using PUBO or some other complex techniques to improve OpenGL rendering. It still explains nothing, but at least it is a guess

  The behavior is the same on Ubuntu, where decoding uses different codec (I mean that using GPU accelerated or CPU accelerated codecs makes no difference !), so, it makes more probable that I’m missing something about OpenGL... or not, because launching 6-7 Qt examples with dynamic textures shows normal growth of CPU usages — it is approximately a sum for the number of windows.

  Anyway, it becomes quite tricky for me to profile the case, so I hope someone could have been solving the similar problem before and could share his experience with me. I’d be appreciated for any ideas, how to deal with the described riddle.

  I can add any pieces of code if that helps.

• for loop from two values in list of dicts with python and ffmpeg

  30 décembre 2019, par Brendon Rathbone

  I’m having an issue figuring out how to do the last for loop in my first really useful python program. I am trying to split a video with ffmpeg based on a bunch of logic to figure out edit points.

  I have a list of dictionaries ’cut_list’ that I have sorting figured out like this

  [{'Cutstart': '01:00:00:00', 'CutEnd': '01:00:05:00'}, {'Cutstart': '01:00:10:01', 'CutEnd': '01:00:15:00'}, {'Cutstart': '01:00:20:01', 'CutEnd': '01:00:25:01'}]

  I then am trying to feed these values to ffmpeg, iterating over the list of dicts like so :

  cutcounter=1
  
  for Cutstart & CutEnd in cut_list:
  
      for k in Cutstart.items() & v in CutEnd.items() :
  
          print(k)
  
          print(v)
  
          intime=Timecode(fps_real, k)
  
          intime.set_fractional(True)
  
          outtime=Timecode(fps_real, v)
  
          outtime.set_fractional(True)
  
          cutfile=str(cutcounter)+".mxf"
  
          print(k)
  
          print(v)
  
          subprocess.call(['ffmpeg', '-i', "C:\\path\\to\\file\\BaseFile.mxf", '-ss', k, '-to', v, '-c:v', 'copy', '-c:a', 'copy', cutfile])
  
          cutcounter=cutcounter+1

  My expected output is to iterate over the list and have chunks of the video split off at those specific timecodes and numbered 1.mxf and count up for every for loop to be recombined with inserted fixes to those timespans. I think after I figure out the for loop I will need to also feed the timecode values as HH:mm:ss:mss instead of HH:mm:ss:ff but that’s not the part that I’m having trouble figuring out yet. Right now I just can’t grok the logic of getting the cutstart and cutend for each timecode to feed into the ffmpeg script.

  Current error as I bash my head against the wall trying to get smarter is : Syntax Error: cannot assign to operator

  I’m definitely inexperienced and have hacked this together from a lot of other helpful posts, but am struggling with sorting and lists vs list of dicts vs tuples etc. and where and when to use each one.

• Remove black frames and sync audio with ffmpeg

  24 janvier 2020, par rahim123

  I’m trying to figure out a way to automatically process .mp4 or .mkv videos that have been manually edited to remove a bunch of segments, leaving many blank spaces (black frames with no audio). I want to remove all but one black frame (although I would settle for removing all of them if it’s much simpler) and then also sync the audio after the video timings change.

  I found this question and tried the three main suggestions :

  1. ffmpeg -i in.mkv -vf mpdecimate,setpts=N/FRAME_RATE/TB out.mkv
  2. ffmpeg -i in.mkv -vf [mpdecimate][] out.mkv
  3. ffmpeg -i in.mkv -vf [decimate][]=cycle=6,[setpts][]=N/25/TB out.mkv

  The first one does eliminate the black segments, but it doesn’t sync the audio. The other two commands don’t work :

  > ffmpeg -i in.mp4 -vf [decimate][]=cycle=6,[setpts][]=N/25/TB out.mp4
  
  ffmpeg version 4.2.1 Copyright (c) 2000-2019 the FFmpeg developers
  
    built with gcc 9 (SUSE Linux)
  
    configuration: --prefix=/usr --libdir=/usr/lib64 --shlibdir=/usr/lib64 --incdir=/usr/include/ffmpeg --extra-cflags='-O2 -Wall -D_FORTIFY_SOURCE=2 -fstack-protector-strong -funwind-tables -fasynchronous-unwind-tables -fstack-clash-protection -Werror=return-type -flto=auto -g' --optflags='-O2 -Wall -D_FORTIFY_SOURCE=2 -fstack-protector-strong -funwind-tables -fasynchronous-unwind-tables -fstack-clash-protection -Werror=return-type -flto=auto -g' --disable-htmlpages --enable-pic --disable-stripping --enable-shared --disable-static --enable-gpl --disable-openssl --enable-avresample --enable-gnutls --enable-ladspa --enable-libaom --enable-libass --enable-libbluray --enable-libbs2b --enable-libcelt --enable-libcdio --enable-libcodec2 --enable-libdav1d --enable-libdc1394 --enable-libdrm --enable-libfontconfig --enable-libfreetype --enable-libfribidi --enable-libgsm --enable-libjack --enable-libmp3lame --enable-libmysofa --enable-libopenjpeg --enable-libopenmpt --enable-libopus --enable-libpulse --enable-librubberband --enable-libsoxr --enable-libspeex --enable-libssh --enable-libsrt --enable-libtheora --enable-libtwolame --enable-libvidstab --enable-libvorbis --enable-libv4l2 --enable-libvpx --enable-libwebp --enable-libxml2 --enable-libzimg --enable-libzmq --enable-libzvbi --enable-lto --enable-lv2 --enable-libmfx --enable-vaapi --enable-vdpau --enable-libfdk-aac-dlopen --enable-nonfree --enable-libvo-amrwbenc --enable-version3 --enable-libx264 --enable-libx265 --enable-librtmp --enable-libxvid
  
    libavutil      56. 31.100 / 56. 31.100
  
    libavcodec     58. 54.100 / 58. 54.100
  
    libavformat    58. 29.100 / 58. 29.100
  
    libavdevice    58.  8.100 / 58.  8.100
  
    libavfilter     7. 57.100 /  7. 57.100
  
    libavresample   4.  0.  0 /  4.  0.  0
  
    libswscale      5.  5.100 /  5.  5.100
  
    libswresample   3.  5.100 /  3.  5.100
  
    libpostproc    55.  5.100 / 55.  5.100
  
  Input #0, mov,mp4,m4a,3gp,3g2,mj2, from 'in.mp4':
  
    Metadata:
  
      major_brand     : isom
  
      minor_version   : 512
  
      compatible_brands: isomiso2avc1mp41
  
      encoder         : Lavf58.20.100
  
    Duration: 00:34:23.62, start: 0.000000, bitrate: 506 kb/s
  
      Stream #0:0(und): Video: h264 (Main) (avc1 / 0x31637661), yuv420p(tv, smpte170m/unknown/smpte170m), 640x480 [SAR 1:1 DAR 4:3], 412 kb/s, 29.97 fps, 29.97 tbr, 1867500000.00 tbn, 59.94 tbc (default)
  
      Metadata:
  
        handler_name    : VideoHandler
  
      Stream #0:1(und): Audio: aac (LC) (mp4a / 0x6134706D), 48000 Hz, stereo, fltp, 86 kb/s (default)
  
      Metadata:
  
        handler_name    : SoundHandler
  
  Stream mapping:
  
    Stream #0:0 -> #0:0 (h264 (native) -> h264 (libx264))
  
    Stream #0:1 -> #0:1 (aac (native) -> aac (native))
  
  Press [q] to stop, [?] for help
  
  [AVFilterGraph @ 0x55ece8def080] Bad (empty?) label found in the following: "[]=cycle=6,[setpts][]=N/25/TB".
  
  Error reinitializing filters!
  
  Failed to inject frame into filter network: Invalid argument
  
  Error while processing the decoded data for stream #0:0
  
  [aac @ 0x55ece8c5be80] Qavg: 222.643
  
  [aac @ 0x55ece8c5be80] 2 frames left in the queue on closing
  
  Conversion failed!

  > ffmpeg -i in.mp4 -vf [decimate][]=cycle=6,[setpts][]=N/25/TB out.mp4
  
  ffmpeg version 4.2.1 Copyright (c) 2000-2019 the FFmpeg developers
  
    built with gcc 9 (SUSE Linux)
  
    configuration: --prefix=/usr --libdir=/usr/lib64 --shlibdir=/usr/lib64 --incdir=/usr/include/ffmpeg --extra-cflags='-O2 -Wall -D_FORTIFY_SOURCE=2 -fstack-protector-strong -funwind-tables -fasynchronous-unwind-tables -fstack-clash-protection -Werror=return-type -flto=auto -g' --optflags='-O2 -Wall -D_FORTIFY_SOURCE=2 -fstack-protector-strong -funwind-tables -fasynchronous-unwind-tables -fstack-clash-protection -Werror=return-type -flto=auto -g' --disable-htmlpages --enable-pic --disable-stripping --enable-shared --disable-static --enable-gpl --disable-openssl --enable-avresample --enable-gnutls --enable-ladspa --enable-libaom --enable-libass --enable-libbluray --enable-libbs2b --enable-libcelt --enable-libcdio --enable-libcodec2 --enable-libdav1d --enable-libdc1394 --enable-libdrm --enable-libfontconfig --enable-libfreetype --enable-libfribidi --enable-libgsm --enable-libjack --enable-libmp3lame --enable-libmysofa --enable-libopenjpeg --enable-libopenmpt --enable-libopus --enable-libpulse --enable-librubberband --enable-libsoxr --enable-libspeex --enable-libssh --enable-libsrt --enable-libtheora --enable-libtwolame --enable-libvidstab --enable-libvorbis --enable-libv4l2 --enable-libvpx --enable-libwebp --enable-libxml2 --enable-libzimg --enable-libzmq --enable-libzvbi --enable-lto --enable-lv2 --enable-libmfx --enable-vaapi --enable-vdpau --enable-libfdk-aac-dlopen --enable-nonfree --enable-libvo-amrwbenc --enable-version3 --enable-libx264 --enable-libx265 --enable-librtmp --enable-libxvid
  
    libavutil      56. 31.100 / 56. 31.100
  
    libavcodec     58. 54.100 / 58. 54.100
  
    libavformat    58. 29.100 / 58. 29.100
  
    libavdevice    58.  8.100 / 58.  8.100
  
    libavfilter     7. 57.100 /  7. 57.100
  
    libavresample   4.  0.  0 /  4.  0.  0
  
    libswscale      5.  5.100 /  5.  5.100
  
    libswresample   3.  5.100 /  3.  5.100
  
    libpostproc    55.  5.100 / 55.  5.100
  
  Input #0, mov,mp4,m4a,3gp,3g2,mj2, from 'in.mp4':
  
    Metadata:
  
      major_brand     : isom
  
      minor_version   : 512
  
      compatible_brands: isomiso2avc1mp41
  
      encoder         : Lavf58.20.100
  
    Duration: 00:34:23.62, start: 0.000000, bitrate: 506 kb/s
  
      Stream #0:0(und): Video: h264 (Main) (avc1 / 0x31637661), yuv420p(tv, smpte170m/unknown/smpte170m), 640x480 [SAR 1:1 DAR 4:3], 412 kb/s, 29.97 fps, 29.97 tbr, 1867500000.00 tbn, 59.94 tbc (default)
  
      Metadata:
  
        handler_name    : VideoHandler
  
      Stream #0:1(und): Audio: aac (LC) (mp4a / 0x6134706D), 48000 Hz, stereo, fltp, 86 kb/s (default)
  
      Metadata:
  
        handler_name    : SoundHandler
  
  Stream mapping:
  
    Stream #0:0 -> #0:0 (h264 (native) -> h264 (libx264))
  
    Stream #0:1 -> #0:1 (aac (native) -> aac (native))
  
  Press [q] to stop, [?] for help
  
  [AVFilterGraph @ 0x558b0d48af80] Bad (empty?) label found in the following: "[]=cycle=6,[setpts][]=N/25/TB".
  
  Error reinitializing filters!
  
  Failed to inject frame into filter network: Invalid argument
  
  Error while processing the decoded data for stream #0:0
  
  [aac @ 0x558b0d2f7e80] Qavg: 222.643
  
  [aac @ 0x558b0d2f7e80] 2 frames left in the queue on closing
  
  Conversion failed!

  I also tried this script, but it also fails to sync the audio. I tried with both .mp4 and .mkv source files. Thanks for the help.