[mythtv] [mythtv-commits] Ticket #2198: Transcode treats some 1080i streams as 1088 and puts a grey line at the bottom after resizing

[Chris Pinkham]

* On Sat Oct 07, 2006 at 12:10:53PM -0400, Steven Adeff wrote:
> >  there are 8 blank rows of pixels at the bottom of every frame.  This patch
> >  strips those off and also calculates the new height/width based on 1080
> >  instead of 1088 if the user specified autoheight or autowidth in the
> >  transcoding profile settings.
> >
> >  Closes #2198 by applying slightly modified patch by wagspat.
> 
> are they actually being stripped or just "ignored"? actually removing
> them will decrease the quality of the encode because of the 16pixel
> blocks, its better to set them to "black" and then set the flag for
> the player to ignore them on playback.

They're being stripped.  Why ignore them?  The transcoder automatically
resizes your desired output size to 16-pixel boundaries when encoding MPEG-4
so it doesn't matter what input size you start with, 1088 or 1080.  By
stripping out the 8 lines of black/gray/grey/whatever at the bottom of a
1080 recording, we don't waste bits reencoding those lines and don't have
to scale it out of the picture during display.

With MPEG-4 transcoding, the end result is that your output image size is
rounded up to the next 16-pixel boundary in both directions
(vertical/horizontal) and we don't have a blank line at the bottom.
The internal player is smart enough to know that 1088 is actually only
1080 and doesn't display this blank line during playback.  This patch
just makes the MPEG-4/rtjpeg side of the encoder just as smart.

--
Chris