[mythtv-users] Transcoding advice (long)

[Hector Vayanos]

Hi,

>I have a MythTV setup with a PVR-250. I would like to record programs,
>remove the commercials, and transcode to an MPEG-4 format to keep them small
>but also to allow them to be played on a Windows PC. I also need the process
>to be automated. I don't plan to watch the programs via Mythfrontend any
>time soon.

I have a very similar setup (PVR-250 on RH9.0), running Myth-TV 0.12 and I 
am interested in the exact same thing.

>Because of my Windows-compatability requirement, the internal encoder is not
>a solution, I therefore have 2 options that I know of. Use nuvexport to
>create a DivX file or use transcode or another program to directly transcode
>the MPEG2 file to DivX. Seems to me that programs other than nuvexport won't
>do anything with the cutlist, so I expect that nuvexport is the way to go.
>The only thing is that some people have suggested that nuvexport is not the
>best tool when the original files are already MPEG-2 as is the case with the
>PVR-250 files. I expect that is due to the process that nuvexport uses of
>decoding or "playing back" the encoded file and then re-encoding it.
>Supposedly that will result in lower quality DivX files than if they are
>transcoded directly from the MPEG-2 originals? If that's the case, I think
>it's probably the lesser of 2 evils since as I said, I don't expect that
>other programs can work with the MythTV cultists, and having an automated
>way of removing the commercials (I assume if I'm going to automate I'll be
>using mythcommflag) is important to me.

Based on some forum discussions, it appears that direct MPEG-2 support was 
added to the latest version of nuvexport (can't remember the number right 
now), but I think this was only done for the SVCD portion. Please correct 
me if I am wrong.

>So, if I am correct (I'm not sure that I am) and I need to use nuvextract,
>then I need some advice on how to get decent transcodes. I just tried a
>transcode from a file that was recorded Video: 480x480, MPEG-2 PS, Bitrate
>3000, Max. Bitrate 6000, Audio: 48000, Layer II, 224kbs. I set nuvextract to
>DivX at 224kbs audio, 1000kbs video, 640x480. The resulting file had the
>audio out of sync by at least 2 seconds! Any suggestions on how to fix that?

I have the exact same problem, except that the a/v offset is typically more 
than 2 seconds. The sound is typically ahead by a whole scene (5-10 seconds).

I would also be very interested in getting some feedback on this problem. 
Nuvexport seems to be a great piece of software and it is quite frustrating 
to not be able to use it.

Thanks,
Hector

>Since the original recording is only kept temporarily, should I set my MPEG2
>recording parameters higher? Should it be at the same aspect ratio as the
>final DivX, or does that matter?
>
>Any suggestions are welcome. I have searched doom9.org quite a bit and still
>don't have a clue! =(
>
>-Andy.
>
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________________________________________________________
Hector Vayanos
Senior Engineer,
Qualcomm Inc.

phone: (858) 845-3011
pager: (858) 636-9655
fax: (858) 658-5006