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• ffmpeg is setting start_time to a negative value on output

  16 mai 2016, par Éric

  We’ve been using an old version of ffmpeg for a while and now we need to upgrade to a more recent version (e.g. 2.6) and we have issues with it while converting .mov to .mp4.

  For instance I have a .mov video file that has two streams, video and audio, both with start_time=0 and when I convert it using :

  ffmpeg -i my_file.mov my_file.mp4

  the output mp4 has an audio stream with start_time=-0.021333.

  The FORMAT section, as shown by ffprobe -show_format -show_streams my_file.mp4
  also has start_time=-0.021333

  The previous version of ffmpeg we were using didn’t have this issue...

  When we play the output mp4 file in a web browser using < video > it’s all good while playing but if we pause the video and seek here and there we notice that all the frames are off by 1. The first frame is duplicated and the last frame is missing !

  In other words :

  dom.currentTime = 0 shows the first frame
  
  dom.currentTime = 1/24 (fps is 24) shows the first frame again
  
  dom.currentTime = 2/24 shows the second frame instead of the third frame
  
  dom.currentTime = 3/24 shows the third frame instead of the fourth frame
  
  ...

  We believe this is caused by the field start_time=-0.021333

  This is a major issue for us...

  It’s repro on chrome and firefox but somehow safari is not having issues with this...

  After googling this we found that we’re not the only one with this issue but it’s not clear what the solution is.

  Someone suggested to use the "-c:a copy" arguments and it worked on some files but gave an error on some others :

  Could not write header for output file #0 (incorrect codec parameters ?) : Invalid argument

  So this doesn’t seem to be a robust solution...

  Any help would be appreciated.

• h264 real time video streaming

  24 mars 2016, par Michal Gallovic

  If you have dynamically generated h264 frames on one end (server), how would you go about making a real time (low latency) video stream viewable in browser (client) ?

  In other words, what I’m trying to achieve is streaming graphically intensive c++ application from gpu server to browser.

  As a simple solution, I’m thinking of something like this :

  c++ app | ffmpeg | server | html5 client

  h264 frames created by application are sent to standard output, where ffmpeg is used to remux this stream into mp4 that is passed to server, which upon request can pass it to client.

  Is this a good approach ? Is that even possible to create a low latency 30fps video stream using this approach ?

• FFmpeg - Writing a script to define fontcolor of each word in a text file ?

  1er mars 2019, par distro.obs

  I have a text file with a lot of word separated by newline character like this

  apple
  
  banana
  
  strawberry

  And I have a list of colors I want those word to appear in

  0xFF0000
  
  0xFFFF33
  
  0xFF0045

  Also I’m using command like this

  x=:'lte(t,10.99)*0+between(t,11,42.99)*10+between(t,43,643.99)*20+gte(t,644)*30':y='lte(t,10.99)*0+between(t,11,42.99)*10+between(t,43,643.99)*20+gte(t,644)*30'

  to move those words around.

  Is it possible to somehow script ffmpeg to color those words and also move them all in one command ?