interlaced video question for you XV experts

[Gene Heskett]

On Thursday 17 March 2005 22:24, Benjamin Herrenschmidt wrote:
>On Thu, 2005-03-17 at 21:18 -0600, Billy Biggs wrote:
>> Benjamin Herrenschmidt (benh at kernel.crashing.org):
>> > Which field comes first in a frame is different between PAL and
>> > NTSC if my memory is correct.
>>
>>   AFAIK, this is a convention and it depends on how it is being
>> stored, and has nothing to do with the actual output (you have a
>> 4-field and 8-field sequence for the colour carrier in NTSC and
>> PAL respectively, but in digital video you don't usually care
>> about that).
>>
>>   In MPEG-2 there is a flag called "top_field_first" which
>> indicates the parity for each encoded frame.
>
>Well, from memory, there is something about the fact that the "top"
> line is either on the first or the second field of a frame that is
> different between PAL and NTSC, no ? That is, on one of them, the
> second field starts in the middle of the screen above the first
> field since scanning isn't exactly horizontal, or something like
> that ?
>
>I don't remember much of this, I wasn't on the HW side though :)
>
>Ben.

You have it essentially correct, Ben.

-- 
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