[mythtv-users] How much space should transcoding HDTV to mpeg4 save?

[ryan patterson]

I'm experimenting with the transcoding my over the air HDTV recordings to
mpeg-4 to save hard drive space.  I enabled transcoding but didn't change
any of the default bitrate values.  I did enable the "scale bitrate
according to capture resolution" option.  I am recording OTA HDTV with a
HDhomerun unit.  Here are my results from the first show I transcoded:

Channel: CBS
Title: Racheal Ray
Original size: 6.8GB
Transcoded size: 6.3GB

Does this look like usual space savings from transcoding?  Half a gig is a
lot, but honestly I was expecting more.  It saved less then 7.5% of the
original file size.  Basically if I transcode everything I can have 107
hours of recordings on a given hard drive size instead of 100 hours.  I
think it would be better to save the cost of the electricity used to
transcode and buy a larger hard drive.

I didn't cut the commercials.  I know that would have saved more space, but
I am not interested in archiving shows.  I just watch once and then delete.
And I don't trust the commercial flagging enough to cut without manually
checking the cuts first.

Am I missing something?  Do I need to adjust some bitrate settings to get
better compression?

-- 
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Ryan Patterson
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