[mythtv-users] MPEG-2 to MPEG-4 Transcoding comparisons

skeeterskip skeeterskip at yahoo.com
Wed Oct 29 04:12:04 EST 2003


What do you guys use to change .vob files to mpeg-4 .avi? Is there a plugin
for mythtv for this?
----- Original Message ----- 
From: "James L. Paul" <james at mauibay.net>
To: "Discussion about mythtv" <mythtv-users at mythtv.org>
Sent: Tuesday, October 28, 2003 11:46 PM
Subject: Re: [mythtv-users] MPEG-2 to MPEG-4 Transcoding comparisons


>
>
> Clif Deanhardt wrote:
> > Actually, I'm just trying to make it as small as possible (while,
> > unfortunately, knowing as little as possible).  Back when I had the CVS
> > running (early september) I had it transcoding 3.7gb files into 700Mb
> > MPEG-4s with no noticable loss in picture quality (to my eyes).  I can't
> > seem to recapture that, though.
> >
> > I assume I'd just drop my MPEG-2/DEFAULT bitrate to 2200 or so and check
the
> > quality... is that right?  Should I expect to get any space savings from
> > converting a 2200 MPEG2 into a 2200 MPEG4?  I have no reason to use
MPEG4
> > other than trying to save space.
>
> It's not the type of codec that saves space, it's the bitrate. (The
> number of bits per second.) 2200kbps is just that, 2200kbps. No matter
> what codec you use (excepting for VBR variations) a 2200kbps 1 hour file
> is going to be approximately 2200kbits x 60 seconds x 60 minutes =
> 7920000kbits = 7734Mbits = 7.734Gbits = 0.967GB. Call it about 1GB per
> hour then.
>
> The quality issue is about which codec gives the best quality at that
> bitrate. MPEG4 is going to be the winner there, but only if it's the
> original codec. You aren't going to transcode from one codec to another
> and get higher quality video, you lose quality each time you transcode.
> (And at low bitrates, the loss can be substantial.)
>
> If it's only size you are after, I wouldn't transcode from MPEG2 to
> MPEG4. Any size savings is likely to be offset by quality loss and heavy
> CPU time. Better to simply encode at a lower bitrate in the first place.
>
> I have about 150GB for video, and at 1.8GB/hour, that's enough for me. I
> have a couple extra profiles set up for higher and lower
> quality/bitrates, but my default is currently 3500k/5000k. Oh, and I
> gain quality by reducing resolution. I use 1/2D1 DVD resolution, which
> is 352x480. This is technically equivalent to SVHS resolution, and most
> CRT televisions are incapable of representing higher resolutions than
> this. When I make a DVD from my 1/2D1 3500kbps MPEG2-PS streams output
> from my PVR-250, it looks absolutely great on a standalone DVD player.
> It's only about VHS quality output from the Myth box, due to my
> GeForceII GTS TV-out not being the greatest.
>
> Set your capture resolution to 352x480 and the bitrate to 2500 or 3500,
> or as low as you decide you like the resulting quality. Play with the
> Live TV profile first, it's easy to just check and see the results.
>
> For comparison, the SVCD standard calls for 480x480 at 2524kbps max. And
> that's overkill. 352x480 looks even better because the extra pixel depth
> significantly increases image quality much more than the extra
> resolution. Try it and see. :)
>
> Anybody interested in the benefits of 1/2D1 or CVD resolution should
> read this:
>
> http://www.dvdrhelp.com/forum/userguides/98177.php
>
> > Clif
> >
> > -----Original Message-----
> > From: James L. Paul [mailto:james at mauibay.net]
> > Sent: Wednesday, October 29, 2003 1:39 AM
> > To: Discussion about mythtv
> > Subject: Re: [mythtv-users] MPEG-2 to MPEG-4 Transcoding comparisons
> >
> >
> >
> >
> > Clif Deanhardt wrote:
> >
> >>Would someone who's using .12 to transcode PVR-250 MPEG-2s into MPEG-4s
> >
> > like
> >
> >>to compare notes on compression rates?  I'm trying to get a handle on
> >>whether I've got mine set up optimally and I'm a bit of a noob at
setting
> >>this thing up.
> >>
> >>With the exception of a apparition when I first started using it, every
> >
> > one
> >
> >>of my 1hr shows records at 3.7gb and after transcoding it's 2.2gb,
> >>regardless of the type of show or number of colors or quantity of
> >
> > movement.
> >
> > I wonder... Is the quality of a 3.7G MPEG2 file transcoded to 2.2GB
> > MPEG4 better or worse than just encoding the original MPEG2 at 2.2G in
> > the first place? I have trouble believing it's better quality and worth
> > the effort, unless for some reason you really want the results as MPEG4.
> >
> >
> >>Likewise, every one of my half hour shows records at 1.8gb and
transcodes
> >
> > to
> >
> >>1.1gb.
> >
> >
> > My PVR-250 bitrate is set to result in 1 hour for 1.8G and looks
> > absolutely great, better than VHS to my eye. I just keep the MPEG2 and
> > prefer not to transcode at all. Then again, I have little use for MPEG4.
> >
> >
> >>Is anyone else similarly set up?  What numbers are you getting?
> >>
> >>Thanx!
> >>
> >>Clif
> >>
> >>
> >>My settings:
> >>
> >>----------------------------
> >>MPEG-2 ENCODERS / DEFAULT
> >>----------------------------
> >>   Width/Height: 480x480
> >>
> >>   Codec: MPEG-2 HARDWARE ENCODER
> >>   Stream: MPEG-2 PS
> >>   Aspect: 4:3
> >>   Bitrate: 4500
> >>   Max Bitrate: 6000
> >>
> >>   Codec: MPEG-2 HARDWARE ENCODER
> >>   SampleRate: 32000
> >>   Type: Layer II
> >>   Bitrate: 384kbps
> >>
> >>----------------------------
> >>TRANSCODERS / MPEG2
> >>----------------------------
> >>
> >>   Width/Height: 480x480
> >>
> >>   Codec: MPEG-4
> >>   Bitrate: 2200
> >>   Max Quality: 2
> >>   Min Quality: 15
> >>   Max Quality Difference Between Frames: 3
> >>   Scale Bitrate for Frame Size: Selected
> >>   Enable High Quality encoding: Not Selected
> >>   Enable 4MV: Not Selected
> >>
> >>   Codec: MP3
> >>   SampleRate: 32000
> >>   Quality 7
> >>
> >>----------------------------
> >>GENERAL
> >>----------------------------
> >>It's configured to automatically detect commercials, but not to skip
them.
> >>And the resulting, compressed files still have the commercials in them.
> >>
> >>
> >>
> >>_______________________________________________
> >>mythtv-users mailing list
> >>mythtv-users at mythtv.org
> >>http://mythtv.org/cgi-bin/mailman/listinfo/mythtv-users
> >>
> >>
> >
> >
> >
> >
> >
> > ------------------------------------------------------------------------
> >
> > _______________________________________________
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> > mythtv-users at mythtv.org
> > http://mythtv.org/cgi-bin/mailman/listinfo/mythtv-users
>
>


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