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• Optimizing preprocessing of data

  12 mai 2018, par WhatAMesh

  I have to preprocess 1-2,5 Terabytes of 1920x1080 videos (in .mp4 format) and try to find the fastest way to do so.

  For every video I have to:

  • Sample at 1 fps
  • Crop two images out of every frame
  • Save the two frames (output format needs to be uncompressed)

  Im currently doing it the following way using ffmpeg:

  def cropVideo(vidInPath, vidOutPath):
              crop = 'ffmpeg -i ' + vidInPath + ' -filter_complex "[0:v]crop=400:200:0:484[face];[0:v]crop=300:50:1624:300[number]" -map [face] -map 0:a ' + vidOutPath + '/face/face.mp4 -map [number] -map 0:a ' + vidOutPath + '/number/number.mp4'
              subprocess.call(crop)
              return
  
  def videoToImageSequence(vidInPath, vidOutPath):
      conv = 'ffmpeg -i ' + vidInPath + ' -vf fps=1 ' + vidOutPath + 'video-frame%05d.png'
      subprocess.call(conv)
      return
  
  cropVideo(dirPath + a + '.mp4', dirPath + a + '/')
  videoToImageSequence(dirPath + a + '/face/face.mp4', dirPath + a + '/face/')
  videoToImageSequence(dirPath + a + '/number/number.mp4', dirPath + a + '/number/')
  

  Is there a faster way to do this?

• how to appending write audio frame use ffmpeg ？

  12 mai 2018, par fredirty2017
  • I found that ffmpeg has a concat protocol that can be used to splice/merge multiple audio files, but it has a param ouput file, that is, a new production to a target file; But I want to have a pattern added to the source file, just like the behavior of the fopen when mode = "a": Appends to a file. Writing operations. End of the file.

  • Is there a direct way to do this?

    FILE *fopen (const char *filename, const char *mode)

• Concatenating a video between a video in ffmpeg

  12 mai 2018, par alan samuel

  I have a function which takes a video with parameters to cut the video between two time points and add in an existing video to it.

  At the moment, I am using FFMPEG to

  1) Convert the video to ts 2) Cut it into two 3) Concatenate the other video

  But after I concatenate and play it on VLC it crashes, but on windows media player it plays but the audio is out of sync.

  Here is what I am doing.

   ffmpeg -i OriginalVideo.mp4 -f lavfi -i anullsrc=channel_layout=mono:sample_rate=48000 -shortest -c copy -bsf:v h264_mp4toannexb -c:a aac -t 00:00:10 firstpart.ts
   ffmpeg -i OriginalVideo.mp4 -f lavfi -i anullsrc=channel_layout=mono:sample_rate=48000 -shortest -c copy -bsf:v h264_mp4toannexb -c:a aac -ss 00:00:15 secondpart.ts
  

  So the first command would convert the video until the 10th second and the second command would convert the video from the 15th second.

  And then I concatenate the videos like this

  ffmpeg -f concat -safe 0 -i list.txt -c copy -bsf:a aac_adtstoasc finaloutput.mp4
  

  list.txt contains

  file 'firstpart.ts'
  file 'tojoin.ts'
  file 'secondpart.ts'
  

  tojoin.ts is a video with a length of 4 seconds. But after its finished concatenating the length in the final output is about 10 seconds.

  Any idea how to fix this ?

• auto resize video resolution with ffmpeg

  12 mai 2018, par Masoud Mohammadi

  I wrote a bash script to convert all video file in a directory. some video resolution is 1280x720 and other 720x1280. how to write a command, if video resolution is 1280x720 convert to 640x360 and video resolution is 720x1280 resize to 360x640 ?

• Build osg with ffmeg plugin

  11 mai 2018, par JayK

  I'm trying to build OpenSceneGraph (OSG) with the FFMPEG plugin. Using:

  • CentOS 7.2 64-bit
  • GCC 4.8.5
  • OSG 3.4.0
  • FFMPEG 2.8

  With FFMPEG, I ./configure with no options, make and make install. In OSG, I cmake ., and make. I get this:

  Linking CXX shared module ../../../lib/osgPlugins-3.4.0/osgdb_ffmpeg.so
  /usr/bin/ld: /usr/local/lib/libavformat.a(allformats.o): relocation R_X86_64_32 against symbol `ff_a64_muxer' can not be used when making a shared object; recompile with -fPIC
  /usr/bin/ld: /usr/local/lib/libavformat.a(amr.o): relocation R_X86_64_32S against `.rodata' can not be used when making a shared object; recompile with -fPIC
  ...(and a ton of others like this)
  

  So I go back to FFMPEG and ./configure --enable-pic. From --help:

    --enable-pic             build position-independent code
  

  make clean, make, and make install.

  I then go to OSG and make and get far fewer, but still get one:

  Linking CXX shared module ../../../lib/osgPlugins-3.4.0/osgdb_ffmpeg.so
  /usr/bin/ld: /usr/local/lib/libavcodec.a(vc1dsp_mmx.o): relocation R_X86_64_PC32 against symbol `ff_pw_9' can not be used when making a shared object; recompile with -fPIC
  /usr/bin/ld: final link failed: Bad value
  collect2: error: ld returned 1 exit status
  

  I did some research on how to tell if an object is built with PIC and found:

  terminal-> readelf --relocs ./libavcodec/x86/vc1dsp_mmx.o | egrep '(GOT|PLT|JU?MP_SLOT)'
  
  000000000ea6  007300000004 R_X86_64_PLT32    0000000000000000 ff_avg_pixels16_mmx - 4
  000000000eb6  007400000004 R_X86_64_PLT32    0000000000000000 ff_avg_pixels8_mmx - 4
  000000000ec6  007500000004 R_X86_64_PLT32    0000000000000000 ff_put_pixels16_mmx - 4
  000000000ed6  007600000004 R_X86_64_PLT32    0000000000000000 ff_put_pixels8_mmx - 4
  

  When I build without --enable-pic, the previous command returns nothing.

  For libavcodec.a, I did nm on it to look for this symbol ff_pw_9, and found these references:

  constants.o:
  ...
  00000000000002d0 R ff_pw_9
  ...
  
  vc1dsp_mmx.o:
  ...
                   U ff_pw_9
  ...
  
  vp8dsp_loopfilter.o:
  ...
                   U ff_pw_9
  ...
  

  What am I missing here?