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

[Niels Dybdahl]

>
> > >        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.
>
> Well, my understanding is that since compressors all rely heavily on
> elimintating redundant information frame-to-frame, frame rate increases
> do not add to the byte count as much as raw pixel resoution increases.
> (Size does not increase linearly with pixels or frame rate, but it
> increases more with pixels than it does with frame-rate.)


But 1080i contains two fields which are from different points in time, so
you have either (1080i) 50 pictures/second of 1920x540 pixels (0.99 Mpx) or
50 pictures/second of 1280x720 pixels (0.88 Mpx). So you only save 10%. On
the other hand moving images (where each 1080i field is different) will be
sampled up from 540 lines to 720 lines and that probably compresses better
than a real 720 line image.

>        d) "Streaming" quality transcodes of SDTV that fit within
> > >            your upstream bandwidth (384K or 512K for example.)
>
> And I should note that long term, a cool tool would be one to
> act like the slingbox and do this in real time.


Isnt this what MythStreamTV is capable of?

Niels Dybdahl
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