[FFmpeg-user] Filter documentation -- PTSs

[Carl Zwanzig]

On 2/14/2021 5:54 PM, Mark Filipak (ffmpeg) wrote:
> On 02/14/2021 08:44 PM, Paul B Mahol wrote:


>> See source code of telecine filter. ...
> I can't read 'C'.

You really ought to learn, it's not that hard to _read_ although the context 
and the data names matter a lot. And there are details that may not be so 
easy to express in text which then just look like the code.


>> ... It is doing all calculations avoiding
>> floats.
>> But formula in floats are pretty trivial and straightforward to write.
> 
> Then my request should be easy for you. What is the formula?

Some of these aren't mere a = b + c formulae, they have decision points in 
the calculation which aren't readily expressed in algebra.

You'll see things like this (from vf_telecine.c/filter_frame)

frame->pts = (
      (s->start_time == AV_NOPTS_VALUE) ? 0 : s->start_time) +
      av_rescale(outlink->frame_count_in, s->ts_unit.num, s->ts_unit.den);

then you need to know what av_rescale does (libavutils/mathematics.c).

Later,

z!