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• ffmpeg video trim - no video only audio

  24 août 2019, par Patrick

  I’m looking for some hints from you.

  I try to trim mp4 videos (mostly 25fps - 720p) with python 3.7 and ffmpeg subcommand.

  Video cut is working fine, but on short videos, below 1 sec, the output.mp4 has no video in it. i tried to view this by VLC and other apps, but still no video in this file. (>1.5 sec its working well with the same input file)

  I have tried this cuts with different video quality, but still same issue.

  Thanks in advance !

  Patrick

  ffmpeg -i test.mp4 -ss 00:00:00.5 -to 00:00:00.9  -c copy test_cut.mp4

  Python code :

  import sys
  
  import subprocess as sp
  
  import os
  
  
  
  from moviepy.tools import subprocess_call
  
  from moviepy.config import get_setting
  
  
  
  #tried different methods and filters, but still same issue              
  
          cmd = [get_setting("FFMPEG_BINARY"), "-i", new_path_in, "-ss", "00:00:"+startSec, "-to", "00:00:"+endSec, "-c:v", "copy","-c:a","copy","-pix_fmt","yuv420p", new_path_out]
  
          subprocess_call(cmd)
  
  
  
          print("cut from "+startSec+" to "+endSec+" done")

• FFMPEG scaling video disable viewing it in HTML player while process is not ended, for video transcoding on the fly

  6 juillet 2022, par Lucas F

  Good day all,

  


  I'm working on a video player with 1080p original video files, and I would like to change their resolution on the fly :

  


  Actually I host all my original video files under a web mp4 1080p format, and I would like to be able to offer 720p, 480p, etc ... qualities.

  


  So I started to look for tutorials about video transcoding on the fly and I found the FFMPEG tool.

  


  I'm actually using the following command to scale videos - to 720p for e.g. :

  


  ffmpeg -i input.mp4 -vf scale=-1:720 output.mp4


  


  The problem is, once FFMPEG starts scaling it, I have to wait the end of the process before being able to play the video. Do you know if there is any parameter for this command to allow playing the video while it's under scaling ?

  


  Or any workaround that can help me doing this ?

  


  Thank you in advance for your help !

  


  EDIT - To allow fragmented video metas

  


  Now I found how to access readable content while transcoding (by transcoding to fragmented MP4) :

  


  ffmpeg -i input.mp4 -vf scale=-2:720 -movflags +frag_keyframe+separate_moof+omit_tfhd_offset+empty_moov output.mp4


  


  But my problem is when opening the video it comes as an "ended" video of the current transcoded data.

  


  So if video lasts 1min and is half transcoded, I'll see only 30s, it will not load more data, once the rest is transcoded.

  


  EDIT - To play entire video while transcoding

  


  I found the following solution that creates a streaming flow througout RTMP protocol :

  


  ffmpeg -i input.mp4 -vf scale=-2:720 -movflags +frag_keyframe+separate_moof+omit_tfhd_offset+empty_moov output.mp4 -listen 1 -f flv rtmp://127.0.0.1:10000/test-stream


  


  My only problem, is that it's not supported into the HTML5 video player, so I tried to convert the RTMP stream to HTTP with the following command :

  


  ffmpeg -v verbose -i rtmp://127.0.0.1:10000/test-stream -c:v libx264 -c:a aac -ac 1 -strict -2 -crf 18 -profile:v baseline -maxrate 400k -bufsize 1835k -pix_fmt yuv420p -flags -global_header -hls_time 10 -hls_list_size 6 -start_number 1 C:\www\test-stream.m3u8


  


  But this is only supported on Apple devices, any idea about how to read this .m3u8 on all other devices ?

  


• 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 ?