[pvrusb2] FAQ addendum for 4:3 recording resolutions

Mike Isely isely at isely.net
Sun Mar 11 01:46:51 CST 2007

On Sat, 10 Mar 2007, roger wrote:

> I think this should be added to the FAQ for the pvrusb2 device.
> The default recording resolution is 720x480, which is not 4:3.
> So, if you plan on recording regular tv/cable broadcasts as I do, it's
> probably best to record shows using a 4:3 compatible resolution such as
> 640x480 or 352x240.  (There are several other variations of resolutions
> compatible for 4:3.)
> This recording 4:3 shows in a non-compatible 4:3 resolution is also
> responsible for the "black bar on sides" issues and aspect problems.


I have a pvrusb2 device set up in MythTV now using the 720x480 default 
capture resolution and I have no such problem.

The capture resolution only remotely relates to the aspect ratio.  Yes, 
for square pixels 640x480 is going to be "correct".  However who says 
pixels have to be square?  The encoded capture aspect ratio is a 
separate parameter in the mpeg stream; apps like mplayer and mythtv must 
use that to correctly stretch / compress the video to match the 
resolution(s) available in the display device.

Try this: Use the sysfs interface to change the aspect ratio.  Don't 
change the resolution; there's a separate control for the aspect ratio 
(ctl_video_aspect).  Observe the results in mplayer...

I suppose one thing that could be said is that if you want square pixels 
then the resolution should be 640x480.

> (I think the above is correct, and if so, probably should be added to
> the fact because I think it's less probable people are using the tuner
> device to record HDTV or other sources through the composite input.)

Not sure I follow this line of reasoning.  It's impossible to record HD 
quality video via the composite (or s-video) input.

> (Now, if I only can get Mythtv to provide good de-interlacing via it's
> transcoders as I doubt we'll be having blue tubes will be making a come
> back anytime soon.)

Yeah, I wish MythTV did deinterlacing as well as tvtime :-(


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