[mythtv-users] Transcoding 101

[C.T. Paterson]

2008/8/1 moodyjunk at frontiernet.net <moodyjunk at frontiernet.net>:
> Before going through the bother of setting up transcoding I need some
> basic information comparing MPEG-2 to MPEG-4 and can't seem to find it
> on the web.  I'm all for saving space, but I want a loss-less recording.

To let you know where I'm coming from; I've got some shows that I
record regularly, commercial strip, and re-encode as mpeg-4s.  At the
end, I have an mp4 with no commercials (not commercial skipped - no
commercials).

> 1) Does transcoding from MPEG-2 (HD cable) to MPEG-4 reduce the
> quality of the recording?

Yes.  In my case, though, still perfectly watchable.  I transcode all
recordings that I plan to keep around.

Ogg Vorbis' sister encoder for video is Theora.  I've now told you
everything I know about it - but it might be worth some investigation
for you if *further* loss (remember - mpeg-2 is lossy) is a big
problem.

> 2) How much space does it save?  10%, 50%?

Using archived Simpsons episodes as examples; the mpeg-2 recordings
(with commercials) are 1.2 gigs.  The commercial-free mpeg-4s clock in
at around 160 megs, give or take.

If we extrapolate the 160 megs to be 22 of the 30 minutes we get
around 220 megs...so about a 80% savings from the re-encoding.

> 3) Can MPEG-4 recordings be played via MythTV Watch Recordings?

Don't know - I personally drop them in my videos folder.

Cheers.

-- 
"My country is the world, and my religion is to do good."
 -- Thomas Paine