Recherche avancée

Sur d’autres sites (3659)

• FFMPEG Audio/Video out of sync after transcoding video in segments

  25 mai 2017, par Idan

  My system transcodes videos in a very specific way.

  1. separating the video and the audio
  2. transcoding the audio stream
  3. segmenting the video
  4. transcoding each of the segments of the video
  5. concat all segments back to 1 video
  6. merging the new transcoded video and audio back together

  While at 99% of the times the process works as it should and the result is a valid video+audio file. in 1% of the times, I get the video and audio out of sync.

  When investigated the issue I noticed that the sync issue appears in a specific segment/s. Meaning, if the video was sliced into 100 segments, the sync can be ok for the first 50 segments, then something happens and the audio or video gets an offset and goes out of sync. It can occur in any number of segments in one video.

  I guess it’s something to do with timestamps getting lost in the process and segments changing their length in the process but I have no idea how I can overcome it. Open for suggestions.

  The commands I use for each step (paths were shorten and may not match, not real issue there) :

  Segmenting the video :

  ffmpeg -fflags +genpts -i $INPUT_FILE -c copy -map 0:0 -flags -global_header -segment_time 10 -break_non_keyframes 0 -reset_timestamps 1 -segment_list segments.list -segment_list_type ffconcat -write_empty_segments 0 -segment_format mp4 -f segment seg-%d.mp4

  Transcoding audio :

  ffmpeg -i $INPUT_FILE  -vn -c:a aac -threads 1 -ac 2 -b:a 125588 audio.mp4

  Transcoding each of the segments :

  ffmpeg -y -i $f -an -vcodec libx264 -threads 4 -r 30 -pix_fmt yuv420p -crf 20 -preset:v fast -profile:v main -level:v 4.1 transcoded/$f

  Concat segments :

  ffmpeg -y -f concat -i segments.list  -c copy -movflags +faststart file_video.mp4

  Combine video and audio :

  ffmpeg -y -i file_video.mp4 -i file_audio.mp4 -c copy -shortest file_out.mp4

• ffmpeg vs mencoder

  17 décembre 2022, par Jonah Braun

  I'm doing a bunch of video encoding for a variety of devices and platforms. I've bounced back and forth a few times between mencoder and ffmpeg. Which do you recommend and why ?

  



  Side question : From googling it seems that mencoder uses ffmpeg. Does it do this all the time or only when it deems necessary ?

  


• Any AS3 solutions for video compression ?

  18 novembre 2017, par Troy Myers

  I’ve been looking around and it does not seem like it is possible with Flash, but is there any way to compress a video file from a mobile device then upload it to a server ? Right now some of my videos are too large (30 mb for 15 seconds) resulting in long upload times. Everything seems to point to ffmpeg but to implement ffmpeg you have to use the NativeProcess which isn’t allowed on mobile devices. Is such a thing possible on the server side via PHP or only client side ? or should I switch to something like Xamarin instead of AS3.

  Thanks !