[mythtv-users] Scaled BluRay video and untouched PGS subtitles wrong size

[faginbagin]

Hi Andre,

On 1/11/2017 4:59 AM, Andre MythTV wrote:
>
>> On 7 Jan 2017, at 20:21, faginbagin <mythtv at hbuus.com> wrote:
>>
>> We got a TV series on BluRay for Christmas and I've been using
>> makemkv to rip and handbrake to transcode down to a smaller size by
>> scaling down the width and height in half (from 1920x1080 to
>> 960x540, 1/4 the area).
>
> That’s not a particularly standard TV frame size so you’ll be
> triggering bugs in any player you try.

I've tried three, mythfrontend, mplayer and vlc. Only mythfrontend has 
this problem.

> You’ll probably get better playback results and most likey avoid the
> subtitle issue by sticking to the original frame size and just
> increasing the compression, or if you must resize use a standard
> resolution like 720p. You state your TV is 720p so the best end
> result you are going to get at the smallest file size will be a
> 1280x720 resize followed by whatever compression you are comfortable
> with.

I've got both 720p and 1080p TVs, mythfrontend demonstrates the bug on both.

> Resizing should always be a last resort with compression, especially
> if the source material is already compressed like Bluray or DVD.

This is a TV show, Prime Suspect, not a recent release movie filmed with 
Hi-Def digital cameras. Most episodes are copyright 1991-1996, the last 
two seasons were 2003 and 2006 respectively. According to this link:
http://www.blu-ray.com/movies/Prime-Suspect-The-Complete-Collection-Blu-ray/72157/
it was shot on Super 16 film, an analog technology. I have a hard time 
seeing any real difference in quality between the 1920x1080 and the 
960x540 versions, even on the 1080p TV. To me, it makes a lot of sense 
to do spatial scaling in whole numbers rather than to scale to a 
standard resolution involving scaling fractional pixels. I doubt that 
scaling to 1280x720 would have produced better quality or compression.

> Alternatively you could keep the makemkv rips and just enjoy the show
> at the quality you have paid for… Bluray is already a seriously
> compressed format and re-compressing already compressed material
> doesn’t usually work too well.
>
> If you wanted 960x540 you could have saved some money and bought the
> DVDs!

There wasn't a big difference in price, and the link above says:
"anyone who has only experienced Prime Suspect on DVD will find these 
Blu-ray presentations a quantum leap in image quality, though obviously 
less than one would expect from a contemporary production shot on hi-def 
video." So I opted to start with better quality source material and see 
if I could compress it enough so as to not exceed my current storage 
capacity without degrading video quality too much. I'm happy with the 
results scaling the resolution 4 to 1.

The subtitle issue is a nuisance, but not enough to re-transcode the 
entire series. If time permits, I might experiment with scaling to 
1280x720 and see if mythfrontend still screws up the subtitles. I'm 
keeping one BluRay rip of one episode for tinkering and to get other 
opinions. Or, I might dig into the code and see if I can fix what I 
think is a bug. A fix that would probably never be reviewed and accepted 
if I'm the only one the the problem.

Regards,
Helen

> Andre
>
>> That gives me files that are about 1/20th the size of the files
>> ripped by makemkv. Handbrake is configured to pass through the PGS
>> subtitles (PGS being the BluRay standard for subtitles).
>>
>> When I play back the result, roughly half of the subtitles are too
>> large and half look OK. I get the same result regardless of the
>> display size (tested on both 1080p and 720p TVs). However, when I
>> use mplayer to playback the same transcoded video, all subtitles
>> are appropriately sized, at least when played on a 1800p TV in both
>> windowed original resolution and full screen modes. I haven't tried
>> mplayer in full screen mode on the 720p TV. But I suspect the
>> result would be the same.
>>
>> So, I'm thinking it's a bug and I'm wondering if anyone else has
>> reported it and whether I should file a ticket. FWIW, I'm running
>> an up-to-date version of 0.27 from the mythbuntu PPA on mythbuntu
>> 14.04.
>>
>> TIA, Helen