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• ffmpeg : drop in sound multiple times at random intervals

  7 septembre 2022, par CoderPadwan

  I have a 2 MP3 files, one is 10 minutes long and another track that is 1 second long. I would like to merge these tracks into a new file that plays the 1 second track at random intervals of the longer one.

  


• ffmpeg video replay with time-sync needs actual recording times

  16 juillet 2018, par navySV

  I am attempting to use ffmpeg to replay multiple video files time-synched, but the zero-based video start time is preventing this.

  I have ffmpeg commands to successfully capture a Microsoft Windows 7 desktop into a video file and replay it with a timestamp value (see below), but the internal timestamp is always starting near zero. How can ffmpeg display the actual time when the video was recorded (and not the time since the start of the video i.e. zero) ?

  For example, if the video started to be recorded at 10:47 am, the ffplay command should display a timestamp similar to "10:47:31" during playback (and not "00:00:31").

  video-capture command :

  ffmpeg -f gdigrab -offset_x 0 -offset_y 0 -video_size 1920x1080 -i desktop -c:v libx264 -preset medium -f mpegts -framerate 24 -y fileA.ts

  playback command :

  ffplay -vf "drawtext=fontfile=/windows/fonts/arial.ttf: text='%{pts\:gmtime\:0\:%H\\\:%M\\\:%S}':box=1:x=(w-tw)/2:y=h-(2*lh)" fileA.ts

  parameters I’ve tried unsuccessfully in the previous commands (including moving these around into different places in the commands) :

  -timestamp now
  
  
  
  -vsync 0
  
  
  
  -copyts

  (every attempt to use -copyts generates errors about "non-strictly-monotonic PTS" or "Non-monotonous DTS in output stream" no matter where I put this parameter)

  -filter_complex "[0:v] setpts=PTS"

  The ultimate goal is to capture four video files (recorded on four different computers and probably having different start times), and then to replay all four in time-sync (which is not possible using only the zero-based start times).

  For example, I’ve been successful at replaying four video files in a 2x2 arrangement, using the following command (I added the -ss parameter to demonstrate I can move the start time of the replay). Unfortunately, they always time-sync to the zero-based first video frame (so they all play from the beginning of the video file). I need the replay to be time-syncing to the actual recorded time for each video. If the four videos were captured starting at times 10:47:00, 10:47:51, 10:48:44, and 10:49:01, I want to be able to replay all of them so that all are displaying the same timestep at the same time (so if one video were displaying 10:48:33, all of the videos would be displaying the same time or a blank screen if that time was unavailable) .

  ffmpeg -ss 00:00:30 -i fileA.ts -i fileB.ts -i fileC.ts -i fileD.ts -filter_complex "[0:v][1:v]hstack[top];[2:v][3:v]hstack[bottom];[top][bottom]vstack[v]" -map "[v]" -timestamp now -f mpegts - | ./ffplay - -x 1920 -y 1080

  Ideally, I would also like to be able to use a real time value (something like "ffplay -ss 10:48:00 ...") to start the video replay at a different position, but worst-case I can write a script to do the needed conversion of the time value.

  My ffmpeg version is a Windows 7 64-bit static build "N-90810-g153e920892" on 2018Apr22 (downloaded from https://www.ffmpeg.org/download.html)

• What happens if I ffmpeg encode two times successively with the same bitrate

  3 juin 2019, par a a

  I have a original divx video (3500k) which I encode to h.264 in a mp4 container. I choose to encode it with 1000 k for instance so that the quality stays close to the original. What happens if I encode it then one more time with the same bitrate ? Theoretically should the quality stay the same ?

  ffmpeg -i A.divx -an -vcodec h264  -b:v 100k A.mp4