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

madshi madshi at gmail.com
Sat Dec 15 20:08:27 CET 2012


> I'd call it something slightly different. For one I'd like to have
> "average" or "default" included in the name because the frame
> (and therefore display) rates may change in a file, and I don't
> want to give the impression that this is fixed for all eternity --
> even though for 99.9999% of all files it will not change.

I understand what you mean. However, I think for true VFR content this
field should not be written at all, or set to 0. An "average" field rate
information for VFR content isn't really useful. If the file maintains the
field rate throughout the whole runtime, then adding "average" or "default"
to the field name is superfluous. If the file does not maintain the field
rate throughout the whole runtime, then the new header field should be left
empty or not be written at all.

Of course that's just my personal opinion. I could live with "default",
too...  :-)

> Third, Matroska's resolution is nanoseconds, not microseconds :)

That's very fine with me.

> DefaultDeocdedFieldDuration -- the period in nanoseconds
> between two successive fields at the output of the decoding
> process

I like this, but I'd prefer it without the "default".

> Sound good, but again, nanoseconds, not microseconds,
> so we'll just have a bunch more zeros and more precision
> in the results:

Then let's be extra precise:

(*)
Examples:
(1) Blu-Ray movie: 1000000000/(48/1.001) = 20854167
(2) PAL broadcast/DVD: 1000000000/(50/1.000) = 20000000
(3) N/ATSC broadcast: 1000000000/(60/1.001) = 16683333
(4) hard-telecined DVD: 1000000000/(60/1.001) = 16683333   (60 encoded
interlaced fields per second)
(5) soft-telecined DVD: 1000000000/(60/1.001) = 16683333   (48 encoded
interlaced fields per second, with "repeat_first_field = 1")

Best regards, Mathias.


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

> Hey,
>
> On Sat, Dec 15, 2012 at 6:47 PM, madshi <madshi at gmail.com> wrote:
>
> > 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.
>
> Sounds reasonable.
>
> >> "FieldDuration" -- is the period (in microseconds) between two
> successive
> >> fields at the output of the decoding process(*).
>
> I'd call it something slightly different. For one I'd like to have
> "average" or "default" included in the name because the frame (and
> therefore display) rates may change in a file, and I don't want to
> give the impression that this is fixed for all eternity -- even though
> for 99.9999% of all files it will not change.
>
> Second, if we include the word "Default" in the name I'd like to make
> it a bit more distinct from "DefaultDuration".
>
> Third, Matroska's resolution is nanoseconds, not microseconds :)
>
> So what about this:
>
> > DefaultDeocdedFieldDuration -- the period in nanoseconds 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:
>
> Sound good, but again, nanoseconds, not microseconds, so we'll just
> have a bunch more zeros and more precision in the results:
>
> > (*)
> > Examples:
> > (1) Blu-Ray movie: 1000000000/47.952 = 20854000
> > (2) PAL broadcast/DVD: 1000000000/50.000 = 20000000
> > (3) N/ATSC broadcast: 1000000000/59.940 = 16683350
> > (4) hard-telecined DVD: 1000000000/59.940 = 16683350   (60 encoded
> interlaced
> > fields per second)
> > (5) soft-telecined DVD: 1000000000/59.940 = 16683350   (48 encoded
> interlaced
> > fields per second, with "repeat_first_field = 1")
>
> Kind regards,
> mosu
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