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• ffmpeg crop in a loop crops files incrementally

  13 septembre 2014, par Voprosnik

  I have a very large audio mp4 file that contains several songs.

  I have generated a script which reads a text file with the times and the song names and successfully assigns starttime, endtime and songtitle in 3 variables. The script successfully echoes the variables and returns the following format :

  00:00:00 00:10:15 Song1
  
  00:10:15 00:14:20 Song2

  and so on...

  Now I am intending to use this script with ffmpeg and crop each part of the big file into smaller audio files.

  The script thus, after feeding the variables in a while loop, it reaches to the command

  ffmpeg -ss $START -t $END -i ${1} -acodec copy $SONGNAME.mp4

  Then I realized that the -t option doesn’t refer to the end point of the excerpt, but the duration. Eg. when I attempted to crop a song from 10:00 to 12:00 it resulted to a 12 minutes long sound file, far longer than the song itself. This resulted in increasingly bigger files.

  Therefore I found some date-manipulating algorithms. Subtracting $START from $END results to an integer with the song’s duration in seconds. I tested it by echoing the results and it resulted to realisting figures (around 100-200).

  However when I replaced the -t option with $DUR instead of $END, this resulted also to increasingly larger files. I didn’t measure the exact length of each, but it seems that the duration increased itself by each loop. I also added an echo $DUR line, which returned the realistic amounts it should. However the ffmpeg -t $DUR did not seem to agree.

  PS. -t has two options, input (before -i) and output (after -i). When I use it after the -i as output (i.e. the duration of the output file) it SEEMS to work, at least it generates realisticly sized files. The question remains why it behaves strangely in the first place.

• How to improve the output video quality with ffmpeg and h264_videotoolbox flag ?

  13 avril 2023, par Anthony Kong

  Currently I am using this command to convert

  


  ffmpeg -i <srcfile> -vcodec libx264 -profile:v main -level 3.1 -preset slower -crf 18 -x264-params ref=4 -acodec copy -movflags &#x2B;faststart <outfile>&#xA;</outfile></srcfile>

  


  to convert some dashcam footage for viewing on an iOS device.

  


  The above command took about 30 min to complete on a 2017 Macbookpro with 16G of RAM.

  


  I want to speed it. One thing I tried is to harness the GPU in the computer. Therefore I added the flag -c:v h264_videotoolbox

  


  It sped up by a lot. I can complete the conversion in 1 min.

  


  However, when I inspected the output, the GPU version suffers from banding and blurry.

  


  Here is a screenshot. CPU version on the left and GPU version on the right.

  


  

  


  To highlight the difference, here are the parts of the videos

  


  

  1. Trees in reflections

  


  


  

  


  

  2. corrugated iron sheet wall

  


  


  

  


  Is there any switch that I can manipulate to make the GPU version clearer ?

  


• ffmpeg - library - libavformat.so.52 incorect configuration path

  4 février 2013, par florin

  I had recompiled ffmpeg on a CentOS 6.3 server.

  Everithing seams to be ok but I got next error into error_log file. :

   PHP Startup: Unable to load dynamic library '/usr/local/lib/php/extensions/no-debug-non-zts-20090626/ffmpeg.so' - libavformat.so.52: cannot open shared object file: No such file or directory in Unknown on line 0

  Here is my ffmpeg configuration :

  root@mail [~]# ffmpeg
  
  ffmpeg version N-49152-g49b729d Copyright (c) 2000-2013 the FFmpeg developers
  
    built on Jan 22 2013 22:26:36 with gcc 4.4.6 (GCC) 20120305 (Red Hat 4.4.6-4)
  
    configuration: --enable-version3 --enable-libopencore-amrnb --enable-libopencore-amrwb --enable-libvpx --enable-libmp3lame --enable-libtheora --enable-libvorbis --enable-libx264 --enable-libxvid --enable-gpl --enable-postproc --enable-nonfree --enable-pthreads --enable-libvo-aacenc --enable-postproc --enable-swscale --enable-avfilter --enable-shared --enable-runtime-cpudetect --disable-stripping --extra-cflags='-O2 -g -pipe -Wall -Wp,-D_FORTIFY_SOURCE=2 -fexceptions -fstack-protector --param=ssp-buffer-size=4 -m64 -mtune=generic -fPIC'
  
    libavutil      52. 15.100 / 52. 15.100
  
    libavcodec     54. 90.100 / 54. 90.100
  
    libavformat    54. 61.103 / 54. 61.103
  
    libavdevice    54.  3.102 / 54.  3.102
  
    libavfilter     3. 33.100 /  3. 33.100
  
    libswscale      2.  2.100 /  2.  2.100
  
    libswresample   0. 17.102 /  0. 17.102
  
    libpostproc    52.  2.100 / 52.  2.100

  What I understand from this is that I had compiled libavformat.54 BUT in ffmpeg.so config there is libavformat.52 .... How can I fix that ?

  Thank You.