[Matroska-devel] requesting "AvgTimePerFrame" or "FieldRate" header field

madshi madshi at gmail.com
Sat Dec 15 18:47:40 CET 2012


Hey,

I think we should stay away from the term "display(ed)" because usually
displaying frames is only done *after* deinterlacing, so we would be
opening up a can of worms again. Maybe we should use a wording which is
somewhat similar to the MPEG2 and VC-1 specs? These specs talk about
decoding output, which is less controversial, I think.

MPEG2: "If progressive_sequence is '1' the period between two successive
frames at the output of the decoding process is the
reciprocal of the frame_rate. If progressive_sequence is '0' the period
between two successive fields at the output of the decoding process is half
of the
reciprocal of the frame_rate."

VC-1: "If the video sequence is signaled as progressive, the period between
two successive frames at the output of the decoding process is the
reciprocal of the frame rate indicated by the FRAMERATE syntax element. If
the video sequence is signaled as interlace, the period between two
successive fields at the output of the decoding process is half the
reciprocal of the frame rate indicated by the FRAMERATE syntax element."

So maybe for MKV we could say:

> "FieldDuration" -- is the period (in microseconds) between two successive
fields at the output of the decoding process(*).

This sentence alone should cover both progressive and interlaced content, I
think. Adding some key examples would help removing any doubt/confusion:

(*)
Examples:
(1) Blu-Ray movie: 1000000/47.952 = 20854
(2) PAL broadcast/DVD: 1000000/50.000 = 20000
(3) N/ATSC broadcast: 1000000/59.940 = 16683
(4) hard-telecined DVD: 1000000/59.940 = 16683   (60 encoded interlaced
fields per second)
(5) soft-telecined DVD: 1000000/59.940 = 16683   (48 encoded interlaced
fields per second, with "repeat_first_field = 1")

Thoughts?

Best regards, Mathias.



2012/12/15 Moritz Bunkus <moritz at bunkus.org>

> Hey,
>
> BTW, I found the place in my source code in which the
> num_units_per_tick/time_unit is multiplied with 2 for progressive
> frames ;) So yeah I'm good now.
>
> Ok then, let's try working on the wording the new element. What about this:
>
> > AvgFrameDisplayDuration -- Average duration a full video frame is
> displayed before deinterlacing and inverse telecine processes are applied(*)
>
> We should also write up something way more elaborate in the section
> pointed to by (*), though I'm not so sure I'm the one to make the
> first proposal for said text. Could you do that, Mathias?
>
> Kind regards,
> mosu
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