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• ffmpeg - multiple output with thumbnails

  9 décembre 2016, par Thomas

  I would like ffmpeg to do the following :

  • read an input mp4 (-i movie.mp4)
  • skip the first 5 seconds (-ss 5)
  • find scene changes and display the frame numbers (-vf "select=gt(scene\, 0.4, showinfo))
  • output #1 - a gif file (output.gif)
  • output #2 - a contact sheet with all the thumbnails (-vf "select scale=320 :-1, tile=12x200" thumbnails.png)

  This will generate the thumbnails :

  ffmpeg -hide_banner -i d:/Test/movie01.mp4 -ss 5 -vf "select=gt(scene\,0.4), showinfo, scale=320:-1, tile=12x200" -vsync 0 thumbnails%03d.png

  this will generate the gif :

  ffmpeg -hide_banner -i d:/Test/movie01.mp4 -ss 5 -vf "select='not(mod(n,60))',setpts='N/(30*TB)', scale=320:-1" -vsync 0 output.gif

  I would like to do both at once with 2 more features :

  • set fps and resolution for the gif ; I would like the gif to represent the whole movie in X seconds, at Y fps (I know the duration of the input movie so I can calculate how often a frame needs to be captured)

  • set the width only for the thumbnail picture (tile=12 for example) and let ffmpeg determine the appropriate height

  I have tried to compose a command line from what I read on this page : https://trac.ffmpeg.org/wiki/Creating%20multiple%20outputs, using the split / map commands but I couldn’t get it to work

• How to use FFmpeg(v 4.0) HwAccell in Android

  21 novembre 2018, par 심상원

  I’m making an app that uses FFmpeg on Android to show the screen.

  I have a few questions to ask you.

  std::vector <avhwdevicetype> GetSupportHwDeviceType ()
  
  {
  
      unsigned int idx {};
  
      std::vector <avhwdevicetype> hwDevTypes;
  
  
  
      AVHWDeviceType hwDevType = AVHWDeviceType::AV_HWDEVICE_TYPE_NONE;
  
      while ((hwDevType = av_hwdevice_iterate_types (hwDevType)) ! = AVHWDeviceType::AV_HWDEVICE_TYPE_NONE)
  
      {
  
          __android_log_print (ANDROID_LOG_DEBUG, __func__, "[Index% d]", idx ++);
  
          __android_log_print (ANDROID_LOG_DEBUG, __func__,
  
                          "[Support Device Name% s]", av_hwdevice_get_type_name (hwDevType));
  
  
  
          hwDevTypes.push_back (hwDevType);
  
      }
  
  
  
      return hwDevTypes;
  
  }
  
  </avhwdevicetype></avhwdevicetype>

  I would like to use hardware acceleration with the above function, and as a result I could not find any type.

  At https://trac.ffmpeg.org/wiki/HWAccelIntro, it says that Android can use MediaCodec. Why can not I retrieve any type from Android NDK with GetSupportHwDeviceType () ?

  The Configure argument used while building FFmpeg for Android.

  --disable-asm
  
  --enable-cross-comile
  
  --disable-static
  
  --disable-programs
  
  --disable-doc
  
  --enable-shared
  
  --enable-protocol=file
  
  --enable-pic
  
  --enable-small
  
  --enable-mediacodec
  
  --enable-jni
  
  --enable-decoder=h264_mediacodec
  
  --enable-opengl
  
  
  
  /* The argument was not supported by ./configure --list-hwaccel in FFmpeg v4.0.3. */
  
  
  
  --enable-hwaccel=h264_mediacodec 

• FFmpeg output video file much smaller than uncompressed input audio file, using option to preserve original audio quality

  17 mars 2021, par Jan

  I attempt to create a video slideshow from a number of image files and an audio file in 2 steps :

  


  

  1. Create a temporary video file from a sequence of image files

  


  2. Add an audio file to the temporary video file with a delay of 5 seconds

  


  


  The audio file is an uncompressed stereo wav file, encoded with a sample rate of 44100 Hz and a bit depth of 32 bits, with a size of 40.1 MB. To preserve the lossless quality of the input audio file I use the option -c:a aac -b:a 192k as per Slideshow Wiki. However, the final output video file has a size of only 4.49 MB.

  


  How can the output video file be about 10 times smaller than the input audio file and still preserve the original lossless quality ?

  


  My code :

  


  ffmpeg -f concat -i slide-sequence.txt -c:v libx264 -r 30 -filter_complex format=yuv420p temp.mp4
ffmpeg -i temp.mp4 -i audio.wav -af "adelay=5000|5000" -c:v copy -c:a aac -b:a 192k out.mp4