[mythtv-users] Transcoding Artifacts (MPEG-2 -> MPEG-4)

ffrr ffrr at tpg.com.au
Thu Dec 15 03:52:07 EST 2005

Cymen Vig wrote:

>I have been experimenting with transcoding the MPEG-2 output of my
>Hauppauge PVR-500 device to MPEG-4. The current settings are are below
>and result in approximately a 50% reduction in file size so a 1 hour
>recording is 2.2 GB in MPEG-2 and 1.1 GB in MPEG-4. I upped the
>bitrate and enabled some of the quality settings after the first
>transcoding attempt resulted in poor quality -- too many blocky chunks
>in the video for my taste. With the settings below the quality is
>better but I prefer the MPEG-2 recordings because the MPEG-4
>compression seems to highlight and make the video noise worse and
>there are some dancing jaggies occasional on faces and other things.
>I've also noticed that attempting to play the MPEG-4 files with
>mplayer results in the wrong aspect ratio as it thinks the video is
>720x480 while it really appears to be 480x480. If I jump around in the
>file with fast forward/rewind it tends to kill X and leave my sound
>output in an usuable state until the system is rebooted.
>Does anyone have some advice on the settings below? Would the
>interlaced settings have any affect on the video coming from a
>Huappauge PVR card? How do the hardware MPEG-4 encoders such as the
>Plextor PX-TV402U compare to software transcoding? I am going to
>continue to bump up the bitrate on the MPEG-4 transcode settings as
>currently I am not happy with the video quailty. It is *very* close
>most of the time but every once in a while some obvious artifacts can
>be seen.
>So any advice on improving quality? As it stands now, I am leaning
>towards giving the system more drive space and skipping transcoding.

I convert to small mpeg4 files for viewing on a Palm Tx.  I have limited 
my minimum quality to 10.  It is much better, but not perfect.  I think 
you should limit your minimum quality, and maybe reduce the bitrate to 
keep the size down at the same time.  The overall result might be better.


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