mythfrontend should crop 1920x1088 video to 1920x1080
Affects | Status | Importance | Assigned to | Milestone | |
---|---|---|---|---|---|
mythtv (Ubuntu) |
Won't Fix
|
Undecided
|
Unassigned |
Bug Description
Binary package hint: mythtv
The broadcast standard for HDTV in North America (ATSC) is defined as 1920 columns by 1080 rows (lines). However, a limitation of the MPEG-2 video standard is that a video must be encoded using blocks of 16x16 pixels. 1080 is not evenly divisible by 16, so the actual broadcast format is 1920x1088 pixels -- the bottom 8 pixels get cropped off by the playback device. Mythfrontend doesn't seem to be doing this correctly.
Most TV stations just encode black in the bottom 8 pixels, but some use a gray bar (my local PBS station, KTCA, currently does this). A black bar usually isn't noticeable, but the gray bar can be quite annoying (note that this gray bar can also appear in transcoded video, so a fix to mythtranscode to crop the video before scaling and re-encoding is also necessary).
Another side-effect is that this can cause video to be scaled awkwardly when being displayed on a 16:9 display, since the ratio of the raw video is 16:9.06666...
Note that there is (or was) also a 1440x1080/1440x1088 format for 4:3 high-definition video, so any fix should probably just generically apply to any video with 1088 lines.
I'm not sure what the story is in Europe or other non-ATSC regions, but since this is a side-effect of a fundamental attribute of MPEG video, the same issue probably exists there too.
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[mike@no5][~]$ lsb_release -rd
Description: Ubuntu 8.10
Release: 8.10
[mike@no5][~]$ apt-cache policy mythtv
mythtv:
Installed: (none)
Candidate: 0.21.0+
Version table:
0.
500 http://
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Thank you for helping to improve Mythbuntu by opening this ticket. The work required to resolve this ticket is too much considering the complexity of the issue / rarity of the problem / man power of the Mythbuntu team. With that being said,
if someone else could write a patch, we will do our best to see that upstream adopts a fix.