[FFmpeg-user] PTS resolution

[Carl Zwanzig]

(just saw Mark's latest as I was about to press send)

On 2/22/2021 9:01 PM, Jim DeLaHunt wrote:
> The time base can be represented as a rational number, e.g. 1001/30000

Usually expressed as the frame rate- 30000/1001 (for NTSC).

If you're starting with mpeg-ps or -ts, 'Presentation time stamps have a 
resolution of 90kHz", so at 29.97fps the PTSs should be 3003.003... apart. 
Since they're whole numbers, that would be 3003, 6006, etc with an extra +1 
every 333 frames.


Jim says: The PTS resolution is slightly under 1/30,000 second.

That suggests ffmpeg is only using 1/3 the resolution available to the mpeg 
formats, of am I misunderstanding something? (I don't have time to dive into 
the code at the moment.)


There's also some interesting stuff at
http://dranger.com/ffmpeg/tutorial05.html
http://cseweb.ucsd.edu/classes/sp03/cse228/ (old, but should be useful)

and
"Understanding Timelines within MPEG Standards" (looks technically intense)
https://ir.cwi.nl/pub/23650/23650B.pdf
which I'll read in the next few days.

Later,


z!