[FFmpeg-user] What the 'fps' video filter does. [was: Re: Matroska (.mkv) time resolution [was: Re: How can I force a 360kHz time base? ] ]

[Jim DeLaHunt]

On 2021-02-27 01:45, Mark Filipak (ffmpeg) wrote:

> I thought that 'fps' just changes the 'frame_rate_code' metadata.


Not at all. Read [1] for part of the story of what the `fps` video 
filter actually does: "Convert the video to specified constant frame 
rate by duplicating or dropping frames as necessary.…"

Read [2] for more of the story: "Make a new video from the frames and 
presentation time stamps (PTSs) of the input. The new video has a 
specified constant frame rate, and new PTSs. It generally keeps frames 
from the old video, but might repeat or drop some frames. You can choose 
the method for rounding from input PTS to output PTS. This affects which 
frames fps keeps, repeats, or drops.…"

[1] http://ffmpeg.org/ffmpeg-all.html#fps-1

[2] http://blog.jdlh.com/en/2020/04/30/ffmpeg-fps-documented/

Best regards,
      —Jim DeLaHunt