Recherche avancée

Sur d’autres sites (10085)

• avformat/matroskaenc : write a CRC32 element on Attachments

  4 octobre 2016, par James Almer

  avformat/matroskaenc : write a CRC32 element on Attachments
  Implements part of ticket #4347
  Tested-by : Dave Rice <dave@dericed.com>
  
  Tested-by : Jerome Martinez <jerome@mediaarea.net>
  
  Reviewed-by : Michael Niedermayer <michael@niedermayer.cc>
  
  Signed-off-by : James Almer <jamrial@gmail.com>
  

  • [DH] libavformat/matroskaenc.c
  • [DH] tests/ref/lavf/mkv

• ffmpeg how to extract X frames every Y interval from url efficiently

  13 décembre 2018, par Luay Gharzeddine

  I’m trying to gather data for a datascience project, and am downloading frames from online videos using ffmpeg. I want to download a subset of the frames in the video, without needing to be precise about which, the only requirement is that they are reasonably spaced apart from each other.

  I have tried

  ffmpeg -i "http://www.somevideo.com" -r 1 -f image2 "image%06d.jpg"

  and

  ffmpeg -i "http://www.somevideo.com" -vf fps=1 "image%06d.jpg"

  and eventually found the following method

  ffmpeg -ss offset1 -i "http://www.somevideo.com" -ss offset2 -i "http://www.somevideo.com" -map 0:v -frames:v 10 -start_number 0 "image%06d.jpg" -map 1:v -frames:v 10 -start_number 10 "image%06d.jpg"

  and all work, but are slow. I have found a hack where I run the following command multiple times, at different offsets, and it seems to be the fastest (where each ffmpeg command is run in parallel multithreaded)

  ffmpeg -ss offset -i "http://www.somevideo.com" -vframes frames_per_fragment -an -start_number start_index "image%06d.jpg"

  this about 25% faster than the previous method

  Is there a faster way to do this ? The issue is that downloading over a network is a bottleneck, so I want to download only the frames I need. I’m looking to download videos/frames in bulk, so any speed improvement would be helpful.

• Segmenting .flac files with ffmpeg truncates audio but not file length

  5 avril 2022, par Yan White

  I am trying to get Twitter spaces audio (.ts) files into a format I can easily edit, on OSX.

  


  So far I was able to convert the files in bulk to .flac with this :

  


  for i in *.ts;
do name=`echo "$i" | cut -d'.' -f1`
echo "$name"
ffmpeg -i "$i" -sample_fmt s16 -ar 41000 "${name}.flac"
done


  


  That worked, and reduced the file sizes somewhat, but..
Because most of the files are around 7 hours long, my editor of choice cannot process that much audio in one file.

  


  So I looked around and was able to find this command to segment the files into 3hr long sections.

  


  ffmpeg -i space-1OdKrBealBqKX_0.flac -map 0 -f segment -segment_time 10800 -c copy space-1OdKrBealBqKX_0__%03d.flac


  


  This works, but each file contains as much empty / silent space at the end as the orginal file. That's going to be a problem for sharing with a team that will help edit these files, as each file has the original file's length and file size. There are a lot of files.
The audio segments and naming did work though.

  


  How to truncate the actual length of the file to the audio segment ?

  


  Caveat : I am no expert on any of these matters, I just managed to google and get this far, so if someone knows and wants to provide working code that would be very much appreciated !