[mythtv-users] transcoding HDTV increases the file size

John Drescher drescherjm at gmail.com
Sun Aug 13 17:08:07 UTC 2006

I had the same issue with 0.19 using regular SD video but it is fixed
in the svn source code and possibly the 0.19.1 fixes release.


On 8/13/06, Patrick Wagstrom <wagspat at iit.edu> wrote:
> 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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John M. Drescher

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