[FFmpeg-user] Decimal times to frame numbers

[Phil Rhodes]

 I must reinforce Carl's interpretation here.
To define the problem more formally, timestamps are a necessary and perfectly reasonable approach to timing video playback in a variable frame rate environment. They're not a particularly good way of looking up specific images in a sequence in a fixed frame rate environment. There's a lot of ambiguity in that a range of times refer to any one image, and applications working in a fixed frame rate environment (which means absolutely all of film and television production) have to make some sort of hopefully-sensible estimated conversion, which can and has caused real world problems. Issues arise particularly when bringing variable frame rate material into a fixed frame rate environment, which may be as simple as video shot on cellphones, which often don't maintain a very consistent frame rate even when asked to.
The reason it feels like there isn't any very obvious and guaranteed-correct way to convert frame counts to timestamps and vice versa is that... there isn't any guaranteed-correct way to do that. That doesn't mean it shouldn't be done.
People involved with the ffmpeg project in the past have made some odd statements about timecode, though; I don't think most of the people involved in the project have much experience of real world film and TV production, so I wouldn't hold your breath for a fix.
P