Subtitle's position jumps

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LouF2
Posts: 7
Joined: Sun Aug 29, 2021 6:05 pm

Subtitle's position jumps

Post by LouF2 »

I am having an issue where when playing videos with subtitles, the subtitle's position jumps from the normal bottom center location to middle left.
I have only seen this happen from files that I've created from Handbrake, and it consistently happens. If I turn off/on subtitles, it returns to bottom cnter but will jump to middle left again. Files created are typically MP4, and I believe I've tried an MKV with the same result. I've made subtitles from SRT and another file already had the subtitle stream in it (this was a conversion from MPG to MP4) - playback actions were similar.

I've posted on Kodi forums, but I didn't get too far there - they passed to either the pre-made image from RetroPie or Handbrake.

I'm posting here because it definitely happens when I use Handbrake.

Thanks


Files are made with:
HandBrake 1.3.3 (2020061300)
Windows 10 Pro

Files played on:
Kodi 18.7
Raspberry Pi 4B-2Gb, 5.10.11-v7l+ firmware, 3A power supply
RetroPie v. 4.7.1 from pre-made SD image on RetroPie
Stored and played from external USB drive



HandBrake Activity Log
https://pastebin.com/dhgTRJ49

Kodi debug log:
https://pastebin.com/tdrVnjUt
Woodstock
Veteran User
Posts: 4614
Joined: Tue Aug 27, 2013 6:39 am

Re: Subtitle's position jumps

Post by Woodstock »

Code: Select all

[01:50:00]  * subtitle track 1, Unknown, Closed Caption [CC608] (track 0, id 0xfe000000, Text) -> Passthrough, Default
The subtitle is not being burned in, but it should be getting converted to an MP4-compatible "timed text" format. Closed Caption tracks can be weird in how the text is placed, but it should be consistent each time it is played.

What happens if you ask handbrake to render the track, i.e., "burn in"? When passing through, you're depending on the player's subtitle renderer to do the right thing, and handbrake really has no control over that.
LouF2
Posts: 7
Joined: Sun Aug 29, 2021 6:05 pm

Re: Subtitle's position jumps

Post by LouF2 »

Thank you very much for replying.

I ran a burned-in run, and what I think I see happening is:

- The text jumps around, but it seems intentional for enhanced placement (i.e. sometimes it is centered-high but that seemed applicable to avoid screen messages such as programming burned-in text of credits or of a person name, etc...)

- Sometimes the text was left-bottom or right-bottom, but that, too, seemed be intentional to be closer to where the person was on the screen. This seemed to happen only when there where two people to caption, and the text did seem to be left- and right-justified (edit: I'm convinced this is intentional).

- Other times, offsetting didn't seem quite necessary and a bit random, but, still, it may be intentional by the authors. (this show's captioning was done by Vixon (?) edit: but this is not displaying today, and the text, "www.Vixon.com" was blue for a long time within a scrolling action)

- As far as Handbrake's burn-in... the text seems to be a bit large, and longer sentences ran off the screen - I'm not sure if these are triggers for the original jumping issue. It is too difficult to test this since the original jumping could happen in one minute or ten minutes.

- Further, captions have been altogether different today in that they don't have a scrolling action in either the original MPG file nor the converted MP4 file (I'm actually forgetting, at this point, with which file that was happening with).


So, yes, it does seem the RPi/Kodi is not handling the caption-rendering as well as Handbrake does (i.e. when HandBrake provided the burned-in rendition). This makes me hope there are switches that can instruct captioning coding differently in HandBrake.

I know this is a lengthy reply, but I'm trying to provide as much info. as possible. I am contemplating converting a number of videos from MPG to MP4 to free disk space, but I'm undecided about garbaging-up the captioning for disk space at this point. I'm not deaf, but I like captioning for clarification, and it seems too valuable to lose.

I hope I'm not S.O.L, but I'm guessing there is nothing to tweak.


Activity Log (burned in):
https://pastebin.com/MvNGrway
Woodstock
Veteran User
Posts: 4614
Joined: Tue Aug 27, 2013 6:39 am

Re: Subtitle's position jumps

Post by Woodstock »

I don't think handbrake's renderer will generate scrolling lines on simple text subtitles. I do know that SSA subtitles can generate many special effects when being burned in, but that would not apply here.

The moving-with-the-speaker behavior I've seen on other subtitles, and yes, it is annoying if you're not accustomed to it. And it's REALLY annoying when you try to use the captioning to clarify what is said, and the subtitle is [indistinct mumbling]!

Fixing this properly would involve extracting the subtitle track and editing it with a subtitle-aware editor, that would let you make the positioning consistent. I cannot make any recommendations on that, since I haven't done it. But it would give you something that will render consistently.
LouF2
Posts: 7
Joined: Sun Aug 29, 2021 6:05 pm

Re: Subtitle's position jumps

Post by LouF2 »

I have found a consistency (by luck). The caption will jump (on my playback system) If the line is over 30 characters. I've repeated it, and it jumps at the same point. Also, if I "rewind", the caption will be normal and then jump at that same point again - so this begins to remove the "randomness".
LouF2
Posts: 7
Joined: Sun Aug 29, 2021 6:05 pm

Re: Subtitle's position jumps

Post by LouF2 »

For follow up and my own record:

Instances where lines less than 30 characters shifted.
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