ffmpeg - setting chapters by framecount instead of milliseconds?

[BabaG]

I've just gone through a process of adding chapters to a file using ffmpeg. Works great but, the way I found to do it required converting the marker placements to milliseconds from the original timecode. Since my editing software will display my files with framecounts, it occurred to me that it might be possible to save some conversion effort by telling ffmpeg where to place the chapter markers using these framecounts.

Here's an example of a chapter marker I placed:

[CHAPTER]
TIMEBASE=1/1000
START=7000
END=291199
title=Chapter marker

I see that the TIMEBASE is set to 1/1000. That means that the START time for this chapter is 7 seconds (210 frames). To what extent will ffmpeg accept a formula as its TIMEBASE? Can I put in something like:

[CHAPTER]
TIMEBASE=1/30
START=210
END=8736
title=Chapter marker

or

[CHAPTER]
TIMEBASE=100/2997
START=210
END=8736
title=Chapter marker

thanks.

[october262]

I've just gone through a process of adding chapters to a file using ffmpeg. Works great but, the way I found to do it required converting the marker placements to milliseconds from the original timecode. Since my editing software will display my files with framecounts, it occurred to me that it might be possible to save some conversion effort by telling ffmpeg where to place the chapter markers using these framecounts.

Here's an example of a chapter marker I placed:

[CHAPTER]
TIMEBASE=1/1000
START=7000
END=291199
title=Chapter marker

I see that the TIMEBASE is set to 1/1000. That means that the START time for this chapter is 7 seconds (210 frames). To what extent will ffmpeg accept a formula as its TIMEBASE? Can I put in something like:

[CHAPTER]
TIMEBASE=1/30
START=210
END=8736
title=Chapter marker

or

[CHAPTER]
TIMEBASE=100/2997
START=210
END=8736
title=Chapter marker

thanks.

try this here - https://www.trekview.org/blog/2022/choosing-right-frame-extraction-rate-ffmpeg/

[BabaG]

Not sure how to read the content in that link but, without a clear (to me) answer, I tested. I'd been nervous about the possibility of breaking something but, as it turned out, both of the formula i posted (1/30 and 100/2997) worked. They both allowed me to input my chapter start times in frames, one for 30fps content, the other for 29.97fps content.

This should make it unnecessary to convert to ms before creating a chapters.txt file for ffmpeg and allow reading frame counts directly from an editing timeline that has the ability to display in frames.

thanks,
babag

[jagabo]

Using the frame duration as the time base so you can enter frame numbers was a good/novel idea!

Note that a duration of 1001/30000 may be more accurate than 100/2997. 29.97 is usually shorthand (rounded) from 29.9700299700299700... (30000/1001).

[BabaG]

thanks, jagabo! will include that in my notes and scripts.

thanks again,
babag