[mythtv-users] Optimal capture resolution for DVD burning

[Michael T. Dean]

On 07/26/06 09:43, JCA wrote:

>    I am currently capturing the video signal from my TV at a 720x480
>resolution. This resolution is set in two places; first, by means of
>the ivtvctl command on my WinTV PVR-150 board, and also in the
>mythfrontend configuration. This works fine. The only problem is that
>the resulting data occupies a lot of disk space: A three hour show
>takes up some 7 GB.
>  
>

File size is determined /exclusively/ by bitrate.  It has nothing to do 
with resolution.  ( 
http://www.gossamer-threads.com/lists/mythtv/dev/74963#74963 )

However, the resolution you use determines a minimum bitrate required 
for a given level of quality.  You're using a bitrate around 5500kbps 
(including audio)--which is likely more bits than required to achieve 
the maximum quality possible for the electronics in the PVR-x50 cards.  
Chances are you won't see any difference in quality with an average 
bitrate of about 4000kbps (and a max of maybe 6000kbps) for video.  See 
http://www.mediachance.com/dvdlab/tutorial/bitrate.html for a nice graph 
showing how quality relates to bitrate and resolution.

>    What I want to do is to capture material and then burn it to a
>DVD. I understand that capturing at 720x480 is overkill, for
>broadcasts in the US do not have that resolution. My question would
>therefore be, What capture resolution should I use, if I want to burn
>the resulting material to DVD to be watched on a 32" or larger TV,
>while keeping the best quality without wasting space? The ideal
>solution would be one that minimizes the processing of the captured
>material for burning to DVD - currently I only have to replex the MPEG
>files created by MythTV, in order to obtain output MPEG files that I
>can directly feed to dvdauthor for the creation of the DVD burning
>file hierarchy.
>

Some who take archiving seriously record at high resolution/bitrate and 
transcode to a lower resolution/bitrate for DVD's.  Others just record 
720x480 and slap the show on the DVD.  For example, Cory Papenfuss (who 
seems to be pretty serious about quality) records at 640x480 with a high 
bitrate (~5Mbps--like yours) and transcodes to 352x480 (Half D1 
resolution) with some filtering ( 
http://www.gossamer-threads.com/lists/mythtv/users/121593#121593 ).  
Note, though, that on a 2.4GHz machine, transcoding takes about 3-4 
hours per one hour show /after/ removing commercials (3-4hrs per ~40min 
of content).

The only resolutions you can burn to DVD are 720x480, 704x480 (which 
isn't appropriate unless you clean the edges of the video), 352x480, and 
352x240.  So, if you record at any other resolution, you have to 
transcode to a DVD-compliant resolution.  Therefore, even though the 
PVR-x50's electronics seem to max out at about 480x480 (and well before 
640x480), the length of time required to transcode to a DVD-compliant 
resolution is great enough that most just record at 720x480.

Personally, I watch and delete shows, and I just record everything at an 
extremely low bitrate (giving about VCR quality).  After all, I watch TV 
for the articles^H^H^H^H^H^H^H^Hstories, not for the pictures.  (Of 
course, that's not preventing me from setting up an HDTV system to go 
with my 67" 1080p TV--which is still displaying SDTV at VCR quality...)

Mike