[mythtv-users] IVTV Bitrate & Resolution

Cory Papenfuss papenfuss at juneau.me.vt.edu
Sun Mar 25 13:50:07 UTC 2007


> b) 720x480 is the maximum DVD-compliant resolution for NTSC format.
> 720x576 is the maximum DVD-compliant resolution for PAL format.  If
> you're recording NTSC, you should /not/ use >480 pixels for the "Y"
> resolution.
>
 	... or <480 for that matter.  NTSC has 480 visible lines with 
interlacing.  Using anything other than ___x480 is generally a bad idea. 
Even 352x480 produces pretty good (VHS-quality) recordings.  352x240 looks 
like crap.  In fact, I recall playing around with that at one point. 
IIRC, recording at 176x480 looked better than 352x240 (same number of 
pixels).

> c) Blurry scenes while recording may be due to using too little bitrate
> for the selected resolution.  If recording NTSC at > 720x480, you'll need
>
 	There is also a temporal filtering option with ivtv that can cause 
that.  It's generally not used, but still a possibility.

> d) Due to the electronics in use on the PVR-x50's, you will be unable to
> improve quality of NTSC recordings by using any resolution > 640x480.
> You will likely be unable to improve quality of NTSC recordings by using
> any resolution > 480x480.  However, due to the scaling issues with the
> PVR-150 and PVR-500 and due to the fact that neither 640x480 nor 480x480
> is DVD-compliant resolution, many people record at the (too-high for the
> electronics) resolution of 720x480.
>
 	704x480 is also a DVD-friendly resolution.  Not much difference, 
but no point in doing 720x480 either.... it's not "more standard"

> e) Regardless of the resolution you finally choose, you /must/ choose an
> appropriate bitrate or you will have poor quality recordings.  a 320x240
> recording with sufficient bitrate will /always/ be better than a 720x480
> recording with too-low a bitrate.
>
 	Right on... also, the required bitrate is a function of signal 
quality and content.  A bad signal with some noise won't compress very 
well and will require more bitrate.  Fast-moving scenes also require more. 
I don't think that the ivtv hardware does a very good job of variable 
bitrate.

> /me wonders if you'll actually scroll down to get to the real reason for
> my post.  If not, those who actually paid attention to the mailing list
> etiquette may find the information beneficial.
>
> Mike

 	The top/bottom/inline posting horse died a long time ago... more 
beating won't do anything.  It boils down to laziness on the part of the 
poster and that will never change.

-Cory

-- 

*************************************************************************
* Cory Papenfuss, Ph.D., PPSEL-IA                                       *
* Electrical Engineering                                                *
* Virginia Polytechnic Institute and State University                   *
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