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• With FFMPEG, create thumbnails proportional to the video's ratio [closed]

  28 janvier 2013, par Felipe Schenone

  I'm using the following command to create thumbnails with FFMPEG :

  ffmpeg -itsoffset -1 -i video.avi -vcodec mjpeg -vframes 1 -an -f rawvideo -s 240x180 image.png

  And it works fine. However, when the video isn't 4:3 ratio, it will still create a 240x180 image, and the extra space will be painted black. Is there some variation of the command that will prevent this and give me an image proportional to the video's ratio ? In other words, I want 240x180 to be the maximum size of the thumbnail, but not the minimum.

  Extra points if the command creates a smaller image when the video is smaller than 240x180.

• RAR Is Still A Contender

  31 mai 2012, par Multimedia Mike — Science Projects, bzip2, compression, gzip, lossless, rar, xz

  RAR (Roshal ARchive) is still a popular format in some corners of the internet. In fact, I procured a set of nearly 1500 RAR files that I want to use in a little project. But I didn’t want my program to have to operate directly on the RAR files which meant that I would need to recompress them to another format. Surely, one of the usual lossless compressors commonplace with Linux these days would perform better. Probably not gzip. Maybe not bzip2 either. Perhaps xz, though ?

  Conclusion
  At first, I concluded that xz beat RAR on every single file in the corpus. But then I studied the comparison again and realized it wasn’t quite apples to apples. So I designed a new experiment.

  New conclusion : RAR still beats xz on every sample in this corpus (for the record, the data could be described as executable program data mixed with reduced quality PCM audio samples).

  Methodology
  My experiment involved first reprocessing the archive files into a new resource archive file format and only compressing that file (rather than a set of files) using gzip, bzip2, xz, and rar at the maximum compression settings.

  echo filesize,gzip,bzip2,xz,rar,filename > compressed-sizes.csv
  for f in `ls /path/to/files/*`
  do
    gzip -9 —stdout $f > out.gz
    bzip2 -9 —stdout $f > out.bz2
    xz -9 —stdout —check=crc32 $f > out.xz
    rar a -m5 out.rar $f
    stat —printf "%s," $f out.gz out.bz2 out.rar out.xz >> compressed-sizes.csv
    echo $f >> compressed-sizes.csv
    rm -f out.gz out.bz2 out.xz out.rar
  done
  

  Note that xz gets the option '--check=crc32' since I’m using the XZ Embedded library which requires it. It really doesn’t make a huge different in filesize.

  Experimental Results
  The preceding command line generates compressed-sizes.csv which goes into a Google Spreadsheet (export as CSV).

  Here are the full results of the bake-off, graphed :

  
  
  

  That’s not especially useful. Here are the top 2 contenders compared directly :

  
  
  

  Action
  Obviously, I’m unmoved by the data. There is no way I’m leaving these files in their RAR form for this project, marginal space and bandwidth savings be darned. There are other trade-offs in play here. I know there is free source code available for decompressing RAR files but the license wouldn’t mesh well with GPL source code libraries that form the core of the same project. Plus, the XZ Embedded code is already integrated and painstakingly debugged.

  During this little exercise, I learned of a little site called Maximum Compression which takes experiments like the foregoing to their logical conclusion by comparing over 200 compression programs on a standard data corpus. According to the site’s summary page, there’s a library called PAQ8PX which posts the best overall scores.

• Converting video formats and copying tags with ffmpeg

  21 mai 2016, par Scott

  I’ve been trying to convert some videos I took on my camera to a compressed format in order to save some storage space. I figured out how to use ffmpeg to convert the videos to the format I want, but what I haven’t been able to figure out is how to copy the metadata. I’d like to copy the original metadata from when the video was taken (most importantly the creation time). I’ve tried running ffmpeg using the -map_meta_data 0:0 option, but that didn’t seem to work. Any ideas ?

  It looks like the data I want to copy in this case is in the format section of the video. Using ffprobe with the show_format option, I get this output :

  [FORMAT]
  
  filename=video.AVI
  
  nb_streams=2
  
  format_name=avi
  
  format_long_name=AVI format
  
  start_time=0.000000
  
  duration=124.565421
  
  size=237722700
  
  bit_rate=15267331
  
  TAG:creation_time=2012-02-07 12:15:27
  
  TAG:encoder=CanonMVI06
  
  [/FORMAT]

  I would like to copy the two tags to my new video.