[mythtv-users] Re: Optimum encoding for remote mythtv

bobnvic at everestkc.net bobnvic at everestkc.net
Thu May 13 13:49:34 EDT 2004


Timothy Weaver wrote:
> Thanks for all the tips and information. I agree with the 
> recommendation to
> record everything at a high resolution and bitrate, then auto-
> transcodeeverything to MPEG4 to shrink the size. I will try this out.
> 
> For my first round of testing, I set the profile "High" for recording
> MPEG-2 at 720x480 with a bitrate of 3500 (max 8000) and audio at 
> 384kbps(48000). The transcode is to MPEG4 at 352x480 with a 
> bitrate of 2200 and
> audio at 80 kbps (48000 because I cannot go lower). Previously, I was
> recording 30 minutes at 500MB and 60 minutes at 1GB. This should
> drastically reduce the size of the files. Now I just have to check the
> quality.

I record at 640x480 with my PVR-250 (don't remember bitrate), then
transcode to MPEG-4 at 640x480 with bitrate of 2200.  I get files at
about the size you stated you previously got (1GB for 1hr).  I don't
believe that transcoding supports changing the resolution - at least
it didn't in the past and I never saw anything that looked like it
changed that.  At MPEG-4 with bitrate of 2200, the video looks perfect
on my system, pretty much identical to the original MPEG-2 which takes
twice as much space.  If you really want to save space I think you should
be able to reduce the bitrate further while still getting a good picture.

> Some questions I have regarding the auto-transcode feature. I read the
> documentation instructions on setting up the auto-transcode but 
> some of it
> is unclear or incorrect.
> 
> 1) The documentation says to enable the "Automatically transcode" 
> option in
> the mythtvsetup program. I don't see this option. Is it only in 
> the CVS? I
> am using .14 from Axel's apt rpms. Or is it referring to the 
> options in the
> mythfrontend TV Settings - Recording Profiles.

It's referring to the Recording Profiles settings.  There is a setting
in mythtvsetup to enable keeping the original files if you'd like.  I
think this is only useful for testing or if you want to keep mpeg-2
versions for svcds.

> 2) I have two sets of profiles: MPEG-2 Encoders (PVR-250 and PVR-
> 35) and
> Transcoders. Both sets of profiles include the option to 
> "Automaticallytranscode after recording". Do I set this option in 
> my MPEG-2 (PVR-250)
> Encoder profile that I use to originally record or do I set the 
> option in
> the Transcoders "MPEG4" profile?

Just in the MPEG-2 profile - I don't think there is any point in setting
it in the transcoders profile.

> 3) Am I limited to automatically transcoding from one profile to 
> one other
> profile? Meaning, can I only go from all recording profiles to a 
> singletranscoding profile? Or is there a way to configure mythtv 
> to, for example,
> transcode all items recorded with the "High Quality" profile to 
> the "MPEG4"
> profile?

Don't know the answer to this one.

Bob
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