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

Moritz Bunkus moritz at bunkus.org
Sat Dec 15 19:49:16 CET 2012


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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