[mythtv-users] transcoding HDTV increases the file size
Patrick Wagstrom
wagspat at iit.edu
Sun Aug 13 16:59:33 UTC 2006
Folks,
I'm trying to wrap my head around some of the transcoding stuff I've
been seeing on my system -- particularly regarding HDTV. I currently
use a firewire connection off a DCT-6200 to record HDTV and a WinTV
PVR-250 to record standard def. My system runs MythTV 0.19. Usually I
get fairly good compression on stuff after cutting commercials and
transcoding for SD. Something like this:
Battlestar Galactica "Pegasus": 1.6 GB => 889.9 MB (Autodetect)
Family Guy "Fifteen Minutes of Shame": 782.8 MB => 462.5 MB (Autodetect)
Not bad at all, takes the file down to 60% of it's original size.
However, for HDTV, the performance is not so great, when recording
Battlestar Galactica in HD off Universal HD, there are a lot of extra
commercials at the end of the program. I take an hour or so of
recording and crop it down to the 37 minutes of actual show. I would
think I should get at least similar compression, approximately 60% of
the original size, but I actually end up with 80%. Maybe that's an
outlier or something, but I'd think that cutting out 40% of the program
would give me about a 40% space improvement.
Battlestar Galactica "Colonial Day": 5.2 GB => 4.2 GB
Here's where it get's really interesting. Many HD programs actually
become larger after transcoding. For example, UHD ran Kindergarten Cop
without commercials the other night. I trimmed it to remove the little
bit before the recording and the little bit after the recording. In
all, I probably cut 6 minutes out of 120 minutes (5%). I wouldn't
expect much of a performance boost. Imagine my surprise when I saw
this:
Kindergarten Cop: 9.6 GB => 11.8 GB (Autodetect)
So, umm, anyone know whats going on?
--Patrick
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