[mythtv-users] HDTV to DVD w/o decode and encode

[Joe Barnhart]

--- Scott Alfter <mythtv at salfter.dyndns.org> wrote:

> What you're asking is impossible; MPEG doesn't work that way.  The
> only
> lossless manipulation of MPEG data that might be possible would be to
> crop the
> frame to a smaller size (you would need to crop by multiples of 16 if
> you were
> to do this) or rotate the entire frame a multiple of 90 degrees. 
> MPEG video
> gets coded in macroblocks of (typically) 16x16 pixels.  To scale the
> video, you
> would have to decode the macroblock, scale it, and create a new
> macroblock.
> For shrinking from HDTV to DVD, each new macroblock would pull data
> from
> several macroblocks in the original video.

Thanks for your response, Scott.  I'd really like to see a good
description of the MPEG2 format and its variations (PS, ES, TS, etc.). 
Even if the "translator" has to decode the macroblocks, wouldn't it
still save time if it could use the same key frames and not have to
choose the frames from scratch, like encoders normally do?

I'm not above trying to create something myself to do this task.  But
I'd need more information on the internal structure of MPEG2 files. 
I've done a couple of googles, but hard information on the MPEG2 file
structure seems to be a little scarce.  I know there are ISO standards
I can buy for some outrageous price (something like $70 ea. for nine
standards).

I just can't believe it's so difficult to get a broadcast HDTV show
onto a regular DVD.



		
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