Cory Papenfuss wrote:
Hey all... I've been chatting on another thread about mpeg2trans
and the structure of the streams produced by the ivtv cards. A couple
of questions about the recording modes of the ivtv chip:
- Aside from encapsulation (TS/PS), is there any discernable
difference between the different types of capture types? PS, TS,
PES_AV, DVD, SVCD, DVD_S1, DVD_S2 all seem to produce the same MPEG
structure... at least the last time I looked.
- Some time between the dim, distant past 18 months ago when I made a
bunch of 8mm tape captures (ivtv-0.1.9), the default GOP structure in
the driver appears to have changed from open to closed. Does anyone
know if the ivtv chip actually utilizes previous GOP reference frames
for a B frame when set to open, or is it just a placebo?
- I've done a little searching on adaptive GOP sizes for the ivtv
chip. For example::
http://www.poptix.net/ivtv/Apr-2003/msg00800.html
Has anyone discovered whether or not this is true? I've seen some
rather ignorant choices made (setting I-frame on first field of an
interlaced scene change, for instance) on the current fixed GOP size.
I think adaptive GOP size could measurably increase the
quality/bitrate if the chip is clever enough.
-Cory
Yes, it includes Scene change detection in the chip. The firmware has a
setting for this but guess what, it is horrible when enabled from my
testing. Basically it's a chip feature that the firmware never was
properly programmed to use, and I suspect heavily it's because the chip
itself wasn't done right and they dropped actual attempts at revising
the chip or fixing the firmware. They did find one good use of that
though, the specsheets or places they sell the chip and list features
:-)). Here's some ideas to play with and see, I never looked at this
more than once, so probably missed something, but it isn't used anywhere
in any official drivers, check the windows mpegs and you'll see the same
mpeg encoding behavior.
// ivtv-streams.c: line #861 or so
// This is turned off by default in the driver right now, this turns it
on ;-)
ivtv_vapi(itv, 0xdc, 2, 8, 1);
// or this, there's two, think this does the same thing in another way?
ivtv_vapi(itv, 0xd1, 1, 1);
Thanks,
Chris
--
===
Chris Kennedy
[EMAIL PROTECTED]
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