Date: Fri, 30 May 1997 19:45:55 +0200 (MET DST) From: Luigi Rizzo <luigi@labinfo.iet.unipi.it> To: hasty@rah.star-gate.com (Amancio Hasty) Cc: multimedia@freebsd.org Subject: Re: bt848 status, comments and diffs Message-ID: <199705301745.TAA20995@labinfo.iet.unipi.it> In-Reply-To: <199705301551.IAA00399@rah.star-gate.com> from "Amancio Hasty" at May 30, 97 08:51:11 am
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> >From The Desk Of Luigi Rizzo :
>
> > The source _frame_ rate is always 30 (25 for PAL), the source
> > _field_ rate is always 60 (50). Now the manual page seems to confuse
> > fields and frames, which makes tests necessary to get the correct
> > interpretation :)
>
> Well, tests over here have shown that for NTSC the source frame rate
> is 30 or 60. I will have to test a little bit more tonite when I get
> home .
It's a matter of definitions of course. In the broadcast video
language, a "frame" is made of two "fields", interlaced. Now, our
interface (ioctl()) to the meteor/bktr video grabber only lets you
ask for:
a) odd+even fields, interlaced; this is 30 different pictures
(which are full frames) per second;
b) odd fields only; call them frames or fields, this is 30
different pictures per second;
c) even fields only; this is 30 different pictures per second;
It is fine to me to allow a video mode which lets you get
d) any single field (odd or even); this gives you 60 different
pictures per second;
it's just that I cannot see how to differentiate between a) and d) when
asking a scaled (say, 320x240) sequence.
To tell the truth, in /sys/i386/ioctl_meteor.h there is a
#define METEOR_FIELD_MODE 0x80000000 /* Field cap or Frame cap */
flag, but it is never used, either in the meteor or in the brooktree
driver.
In other words, if you are getting 30 pictures per second, interlaced,
when requesting odd+even fields at 640x480 (or perhaps even down to
some smaller size, say 328x248), I don't see why you should suddenly
get 60 pictures per second just because you reduced the scaling to
320x240. Sounds like a very odd interaction between image size and
frame rate, and frankly, even if the previous drivers acted this way, I
prefer the picture rate to stay the same, no matter how I scale the
image!
Cheers
Luigi
-----------------------------+--------------------------------------
Luigi Rizzo | Dip. di Ingegneria dell'Informazione
email: luigi@iet.unipi.it | Universita' di Pisa
tel: +39-50-568533 | via Diotisalvi 2, 56126 PISA (Italy)
fax: +39-50-568522 | http://www.iet.unipi.it/~luigi/
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