[mythtv-users] Transcoding to 480p

[Brian McEntire]

Thank you Robert!

Can anyone add on to this? I'd like to use mytranscode or nuvexport. I 
couldn't find a man page for either, but if someone will point me to docs, 
I'll gladly read them.

I'm trying to transcode 1080i and 720p down to 420p (852x420 pixels). I 
would like to keep the bit rate as high as necessary to keep as close to the 
original quality as possible but granted, throwing out 1/2 of the 
information which won't display on my TVs native resolution anyway.

Can anyone recommend a command line? I wanted to do some initial tests 
before setting up any automatic transcoding.

Is MPEG4 considered to be higher quality or easier on decoding for playback 
compared to MPEG2? I'm much less concerned about encoding performance/time; 
playback quality and playback resource usage or my primary concerns. If 
possible, it would be great if transcoded HTDV (down to 420p) plays 
reasonably smoothly on a 1.6 MHz P4.


On 9/5/05, Robert Tsai <rtsai1111 at comcast.net> wrote:
> 
> On Mon, Sep 05, 2005 at 02:00:42PM -0400, Brian McEntire wrote:
> > I have an EDTV that doesn't go to full HDTV specs. It can display
> > 480p, 720p, and 1080i formats, but it's native resolution is 852x420
> > so any of the other formats are going to be downsampled.
> >
> > I'm having success recording HDTV over ATSC OTA with MythTV, but
> > playback is choppy and I know it is because my computer is currently
> > underpowered. I could upgrade, and probably will, but in the mean
> > time, and even after I upgrade, there is no reason to have HDTV
> > shows at higher than 480p since they need to be downsampled to
> > display on my TV anyway.
> >
> > Can I save disk space and possibly improve playback performance with
> > transcoding? How to I manually and automatically set shows recorded
> > in 1080i or 720p to be transcoded down to 480p?
> 
> I have a similar setup as you (record HDTV OTA for display on my
> "HDTV" with only 856x480 resolution).
> 
> Using the internal myth transcoder (mythtranscode):
> 
> In the setup menus, enter the "Recording Profiles", "Transcoders" and
> set up the target resolution to be whatever you want it to be (e.g.,
> 852x420) and some bitrate (I use 4400kbps with the bitrate scaled
> against a 640x480 resolution, to end up with about 2GiB/hr) for the
> "High Quality", "Medium Quality", and "Low Quality" transcoders. There
> are no predefined defaults; you have to set them up yourself.
> 
> In the "Default" recording profile, enable the "auto-transcode"
> checkbox. This checkbox is for mixed systems where one might want to
> auto-transcode recordings captured from an HD-3000 (say), but not
> re-encode recordings captured from a PVR-x50 card that has
> hardware-assist.
> 
> Then in your recording schedules, enable auto-transcoding for that
> recording schedule.
> 
> Other people use nuvexport and "user jobs", but this requires more
> configuration. I think the trade-off is that mythtranscode is
> optimized for speed over quality, while nuvexport takes longer but
> produces higher-quality results for a given target filesize. But I
> don't use nuvexport so I can't say from my personal experience.
> 
> --Rob
> 
> 
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