[mythtv-users] Analog firewire recordings end early due to 25% fewer frames

Yeechang Lee ylee at pobox.com
Wed Feb 4 14:35:39 UTC 2009


David Brodbeck <gull at gull.us> says:
> If they're really being delivered to the cable box as analog signals, 
> they can't be chopping out frames.  Otherwise an analog TV would fail to 
> sync to them.  NTSC equipment is only designed to run at one frame
> rate.

I can't explain what I've seen for the past 15 months in any other
way. The framerate of the post-September 1997 analog-channel
recordings upon playback, as well as comparing before and after
elapsed times, file sizes, etc. are all consistent with an exactly 25%
cut in the analog signal from the normal 29.97/30fps for 480i as of
September 1997. The recordings all play at proper speed--just with
noticeably more fuzziness and less-smooth pans than before--so I don't
know exactly how the bandwidth throttling is done, but trust me when I
say that it is obvious visually.

I presume that the box is designed to auto-fix framerates on the
component output jacks to 30fps/60fps regardless of the signal it
receives from the provider, but I don't know enough about this topic
to be sure. I have never tried the coax or composite jacks.

> Or maybe they're providing a digital version of these channels for
> the cable box to decode?

The analog channels are still definitely coming into the boxes as
analog. Even aside from the (non) FireWire failure of the digital
channels, the difference in visual quality is obvious.

If you're asking whether (as many providers do) the company simulcasts
the analog channels on a separate set of digital channels, the answer
is sadly no, according to the provider's channel listings. Believe me,
I'd be very happy were this the case.

-- 
Frontend/backend:	P4 3.0GHz, 1.5TB software RAID 5 array
Backend:		Quad-core Xeon 1.6GHz, 6.6TB sw RAID 6
Video inputs:		Four high-definition over FireWire/OTA
Accessories:		47" 1080p LCD, 5.1 digital, and MX-600


More information about the mythtv-users mailing list