[mythtv-users] Transcoding and deinterlacing, and other transcode issues

Niels Dybdahl Niels at Dybdahl.dk
Wed Jun 14 07:15:11 UTC 2006

> As for the number of profiles an HD user needs, here are the ones I
> think could be handy:
>         a) Transocde 1080i to 720 lines, for people with 720 line TVs
>         for whom storing the extra megapixel is of limited value.
>             Goal: Reduce size, but lose no quality you would see on
>             your TV.   De-interlace the 1080i of course before
>             resizing.

How do you save size with that? 1080x1920x25 is 51.84 Megapixel/second while
720x1280x50 is 46.08 Megapixel/second. There is hardly any difference
between those numbers.

        b) Transcode both 1080i and 720p to 1280x720 recordings at lower
>             bitrates for long-term disk space saving.    Traditional
>             transocding purpose, for which one may wish high, medium
>             and low qualities.     For people with 1080 line TVs, they
>             would possibly want different targets for 1080i than for
>             720p.   1280x540 and 960x540 are common targets for
>             "near HD" in a small filesize.
>         c) Basic mpeg-4 encoding at about half the size of MP2 but
>             similar quality.

I would use MPEG4 as target for b), so b) and c) is the same to me.

        d) "Streaming" quality transcodes of SDTV that fit within
>             your upstream bandwidth (384K or 512K for example.)

One more possible target: DVD resolution, but that is taken care of by

Of course it would be nice to select whether the output should be
deinterlaced or not. The transcoding system does even allow adaptive
deinterlacers, which are prohibited while viewing because of
CPU-requirements. Are there any adaptive deinterlacers available that could
be added as a user job?

And as a user from a small country, it would be nice if the transcoding
could handle DVB-subtitles. A workaround might be to extract the subtitles
as a user job with ProjectX and then merge them again after transcoding.
Does anyone know if the .nuv format allows DVB-subtitles and would MythTV
show such subtitles in a .nuv file?

Best regards
Niels Dybdahl
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