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• What are good settings for transcoding videos uploaded to my app ?

  14 mai 2020, par Dmitry Minkovsky

  I am working on an app that allows users to share videos. The problem is that many videos are very high bitrate. For example, A 4-minute H264 video from an old iPhone is encoded at 1080p and runs 17,000 kb/s ( 500 megabytes). Accepting and distributing such videos at this bitrate/resolution is not practical for a social application.

  



  I have been playing with ffmpeg to transcode videos to smaller sizes and higher compression, but have not achieved acceptable results. For example :

  



  ffmpeg \
    -i in.mov \
    -vf scale=w='if(gt(iw\,ih)\,780\,-2)':h='if(gt(iw\,ih)\,-2\,780)' \ 
    -c:v libx264 \
    -crf 28 \
    -preset medium \
    -pix_fmt yuv420p \
    -movflags +faststart \
    out.mp4


  



  This command transcodes the above-mentioned 500MB file down to 70MB. It scales the larger dimension of the video to 780 pixels and compresses the video quite a bit. The results are okay, but the file is still large.

  



  Taking the longer dimension down to 480 pixels, the file is reduced to 40MB. Still quite large, and now significantly degraded. Also, the transcoding still takes quite a long time : about 1-1.5x on my 4 year old i7 Macbook Pro with 16GB RAM.

  



  I'm not sure how to improve on this. H265 is not supported in browsers. I am wondering :

  



  

  • How can I reduce size further ?

  


  • How can I transcode faster than 1x without significantly reducing quality ? Even 2-3x doesn't seem great ?

  


  



  Is this as good as it gets ?

  


• Livestream of prerecorded flv videos with ffmpeg and red5

  6 octobre 2014, par user2060812

  My goal is to acheive the following steps :-

  1. rtmp livestream of prerecoreded flv videos using ffmpeg.
     
  2. videos should be played continuously just like a tv station.
     

  We are currently using red5 and ffmpeg to acheive this goal and we have successfully published the live stream of prerecorded single video to jwplayer using the following conversion command :

  for i in *.avi; do ffmpeg -i $i -acodec copy -vcodec copy -f flv rtmp://localhost/oflaDemo/livestream

  But the problem comes when we need to livestream two videos one after the other. User have to click play button again in order to stream second video which is not a tv-station thing instead we need to continuously play stream for user instead of clicking on play button on ending of each stream.

• How does big companies transcode/encode videos so fast ?

  24 avril 2022, par Emir Geçir

  For example how does Facebook, YouTube, Reddit and many countless sites encode videos so fast ? Do they all have in-house solutions ? Tools like FFMPEG and Handbrake are alot slower to how they process files.

  


  I had a hard time deciding if this should be posted on the softwareengineering stackexchange then decided stackoverflow seemed more fit for the question.