Currently testing .ass subcaps in a VFX workflow.
The goal is to drop specfic text over specific shots and the in/out points have
to be frame accurate
We're working in a 23.976 project.
Currently having no trouble using FFmpeg to generate frame-accurate subclips of
individual shots from a full-show export by converting hh:mm:ss:ff to seconds
and then handling the 24 to 23.976 offset, using the following alorithm:
InPoint_Seconds = ConvertToSeconds(InPoint_Hmsf_FullShow) -
ConvertToSeconds(Start_Hmsf_FullShow) // Convert from SMTPE Time Code to
seconds.
InPoint_Seconds = InPoint_Seconds * (1001 / 1000) //Handle 24 to 23.976
offset
OutPoint_Seconds = [Same idea as above]
Duration_Seconds = Output_Seconds - InPoint_Seconds
> ffmpeg -ss InPoint_Seconds -t Duration_Seconds -i SourcePath -c copy
DestPath
So generating frame-accurate copies of portions of a larger file works with
perfect accuracy
BUT when applying the same logic to subcaps using .ass files, sometimes they
land with frame accuracy, and sometimes they don't (They'll be 1 frame late at
most, and it does not increase over the span of the source clip).
Curious if anyone has any ideas.
- Chris C
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