[mythtv-users] Re: Settings vs file size question

Preston Crow pc-mythtv04 at crowcastle.net
Sat Nov 27 23:30:02 UTC 2004


On Sat, 2004-11-27 at 18:09, Donavan Stanley wrote:
> On Sat, 27 Nov 2004 17:48:59 -0500, Don Brett <dlbrett at zoominternet.net> wrote:
> > In an earlier test I found virtually no difference in the file size when
> > varying the video width (320 vs 480 vs 640).  Does that make any sense?
> 
> Resolution has no effect on file size.  It's all in the bitrate.

Technically correct.  The bitrate is the number of bits per second that
the file will consume on average.  However, the combination of bitrate
and resolution determines the quality of the image.  Below a given
bitrate, you'll get a better picture if you lower the resolution.

Personally, I prefer to record at a fairly high quality (2.25GB/hour)
with my PVR-250 card.  When I run low on disk space, I set up cutlists
to extract commercials on shows we won't be watching soon and transcode
them (generating files around 750MB).  In general, you can use a lower
bitrate with MPEG-4 and get the same quality as with MPEG-2.  With the
right settings, you should be able to get 350MB/42-minutes (hour without
ads) perfectly watchable.

If you're going to transcode from MPEG-2, always record in very high
quality to begin with so that you don't have double the digital
artifacts.

--PC




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