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

Clif Deanhardt mythtv at deanhardt.com
Wed Oct 29 02:28:21 EST 2003


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.

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.
>
>
>
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