[mythtv-users] Single Pass Mpeg-4 Transcoding Quality

[Lachlan McIntosh]

Yeah reducing the resolution seems to be a bit of an issue.

I'm recording from DVB-T. So the file comes in as SDTV(?) MPEG-2 720*576
at about 15000 kps (so I get >really< large files).

Even if you change the resolution for the transcode setting for mpeg-2
it seems to keep the resolution of the original
File. Is this expected behaviour? Or am I doing something wrong?

I have tried to increase the bit rate significantly, but even at 2200
Kbps, I still get a lot of jaggies.

I've done some further research on OpenDivx VBR 1/2 pass and according
to "www.spin.net.au/~imroy/content/Tips/capture.html" (which you will
have to read from google cache by the look of it) the attached (below
for future reference - as the original page is down) Shell scripts can
help with MEncoder to do a 2 pass VBR encode.

So this leads to some questions:

Am I barking up the wrong tree here?  
Will 2 pass VBR give me the quality at the file size that I'm looking
for?  (350Mb for a 30-40 minute show - two per cd for archive)
Can Transcode currently resize the resolution of a file?
Has anyone else seen the change from 16:9 to 4:3 after transcode?
If I get this working will it help anyone else (is someone else looking
for this?) 
Has someone else started to look at this that would like to work with me
or who could point me in the right direction?

Thanks

Lachlan McIntosh



--------
 
Attached Shell scripts:

nuvrec.sh


#!/bin/sh

NAME=$1
shift

exec nuvrec -s -vq 85 -w 384 -h 576 -deint cubic -N 16 $@ -o "$NAME.nuv"
nuv2divx.sh


#!/bin/sh

NAME=$1
BASE=${NAME%.nuv}

# Width and height of output
W=384
H=288
# mencoder options
AUDIO="-oac mp3lame -lameopts vbr=2:q=6:mode=1"
VIDEO="-ovc divx4 -divx4opts br=1024:key=250:q=5 -sws 2 -vop
scale=$W:$H,pp -npp hb,vb,dr"

# 2-pass
rm frameno.avi
mencoder "$BASE.nuv" $VIDEO $AUDIO -pass 1 -o "$BASE-1.avi"
mencoder "$BASE.nuv" $VIDEO -oac copy -pass 2 -o "$BASE.avi" && rm -fv
"$BASE-1.avi"



-----Original Message-----
From: mythtv-users-bounces at mythtv.org
[mailto:mythtv-users-bounces at mythtv.org] On Behalf Of Donavan Stanley
Sent: Monday, 29 November 2004 3:51 AM
To: Discussion about mythtv
Subject: Re: [mythtv-users] Single Pass Mpeg-4 Transcoding Quality

On Sun, 28 Nov 2004 16:38:07 +1000, Lachlan McIntosh
<lachlan at directions.com.au> wrote:
> A Transcoded Myth File:
>     Video :  636 MB,  1118 Kbps,  25.0 fps,  720*576 (4:3),  DIVX =
> OpenDivx v4,    Supported
> 
> Settings from "Home Movies" from a friend in the USA.
>  Video :  282 MB,  945 Kbps,  23.976 fps,  624*352 (16:9),  XVID =
XVID
> Mpeg-4,    Supported
>  Video :  301 MB,  978 Kbps,  23.976 fps,  624*352 (16:9),  XVID =
XVID
> Mpeg-4,    Supported
> 
> The "Home Movie" is of significantly higher quality.

The "home movie" is compressing fewer pixels per frame with a slightly
lower bitrate.   Either decrease the resultion you're capturing at or 
raise you bitrate to adjust for the extra pixels.