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• How to read a video stream(H.264) bitrate via ffprobe if the video is VBR

  26 janvier 2021, par Sean
  

  1. if the video stream is VBR, which means the bitrate is variable, so how to read the bitrate via ffprobe ?

  


  2. How to get know the video stream is CBR or VBR ?

  


  


• How to replace a snippet in a video without reencoding the whole video

  3 novembre 2022, par Simon Streicher

  I am trying to edit and replace a section of a video without reencoding the whole video.
Here are the steps I think I need to take :

  


  1. Find keyframes

  


  input :

  


  ffprobe -v error -select_streams v:0 -skip_frame nokey -show_entries frame=pkt_pts_time -of csv=p=0 'example.mkv'


  


  output :

  


  0.000000
1.001000
11.011000
13.430000
20.812000
30.822000
40.832000
50.842000
⋮


  


  2. Export relevant section

  


  For example, export the snippet 40.832000 → 50.842000.

  


  3. Edit and reencode

  


  After editing that section, I need to reencode it to the original codecs for compatibility with the surrounding video. For example, this is the original codecs :

  


  Stream #0:0: Video: hevc (Main 10), yuv420p10le(tv, bt2020nc/bt2020/smpte2084), 3840x1600 [SAR 1:1 DAR 12:5], 23.98 fps, 23.98 tbr, 1k tbn, 23.98 tbc (default)


  


  4. Inject edit back into the video stream

  


  Finally, I need to use FFmpeg somehow to retain everything from the original file (audio, subtitles, chapters, etc.) and to construct a new video stream (for example, Stream #0:0) that is exactly 0 → 40.832000 of the original, the whole edited section, and 50.842000 → end of the original section.

  


  My main questions are :

  


  

  • A. How do I trim the video stream in 2. without reencoding ?

  


  • B. Assuming that the edited video's resolution will remain the same, what is the command for FFmpeg to encode my edit to the codecs in 3. (and would the video be concatenable with the original video) ?

  


  • C. How should I go about glueing the sections together ? Should I simply trim Stream #0:0 into sections v1 = 0 → 40.832 and v2 = 50.842 → end and then concatenate a new stream as new = v1 + edited + v2 ?

  


  • D. How do I replace Stream #0:0 with new ?

  


  


  And probably the most important question : are my assumptions correct and can this be achieved ?

  


• I want to reduce video file size but still have a good video quality, how should I write the code using ffmpeg ?

  9 décembre 2019, par Inibuat Maengame

  First of all, I’ve downloaded some videos to watch, and each file has more than 500MB file size. But due to the vast amount of videos I have at the moment, my 3 external hard drives are crying.
  Up till today, I’ve been using BENCOS to reduce the size...
  I always set the preset to very slow, codec h264, profile : high, and the mode is (probably) fixed bitrate on 736kbps.
  With those settings,
  I was able to reduce the size from 400-600MB into 100-110MB with acceptable video quality.
  But, since BENCOS has stopped its service since ages ago, I’ve been trying FFmpeg lately.

  Using those same settings, -crf 22, -preset veryslow, profile:high, the file size doesn’t really reduce that much... from 500MB to 200MB-ish with a much lower video quality compared to BENCOS.

  How are you guys able to reduce the file size by a huge margin compared to the original but still retain the quality using FFmpeg..?
  what commands I should put into the FFmpeg to get a result as good as BENCOS..?

  Thanks in advance...