Opened 7 years ago

Last modified 7 years ago

#11137 accepted Bug Report - General

Misformed Captions/subtitles

Reported by: jens@… Owned by: Jim Stichnoth
Priority: minor Milestone: unknown
Component: MythTV - Captions Version: 0.25-fixes
Severity: medium Keywords: Captions misformed
Cc: Ticket locked: no

Description (last modified by Kenni Lund [kenni a kelu dot dk])

I use Mythbuntu 0.25+fixes

I rip my dvd's with Handbrake to m4v or mkv container format using x264 codec. I rip the subtitles for danish - my native language. They are not burned in but rather included as default subtitle in the video file.

When i play back the videos in Mythtv the subtitles are crude to look at and have a thick contrasting frame around each letter.

When i play the same video file in VLC the subtitles are normal and nice to lokk at and easy to read.

Capture of video played by Mythtv:
http://postimage.org/image/to37bns4r/

Capture of same video played by VLC:
http://postimage.org/image/aezvulcvr/

Change History (11)

comment:1 Changed 7 years ago by Kenni Lund [kenni a kelu dot dk]

Description: modified (diff)
Type: Patch - Bug FixBug Report - General

comment:2 Changed 7 years ago by Raymond Wagner

Are these the original bitmapped subtitles off the DVD, text subtitles OCR'd from the bitmaps, or the closed captions feed?

comment:3 Changed 7 years ago by jens@…

I have uploaded a small sample of such a video on: http://www.kjellerup-hansen.dk/loa.m4v

It is a sample of the standard rips i make of my DVD's with Handbrake. Subtitles is not burned in but saved inside the m4v stream as default subtitle. /jk

comment:4 Changed 7 years ago by Jim Stichnoth

Status: newinfoneeded_new

Could you create a small sample that illustrates the problem? If it's 2MB or smaller, it can be directly attached to the ticket.

comment:5 Changed 7 years ago by jens@…

In my original posting I have made two screendumps of the same video played back with subtitles by mythtv internal player and by VLC respectively.

In comment 3 there is a downloadable sample of a video. The subtitles start 1 min 35 secs from the start if subtitles are enabled during playback.

comment:6 Changed 7 years ago by Jim Stichnoth

Status: infoneeded_newnew

Sorry, I thought it was a broken link, but it was a broken browser.

comment:7 Changed 7 years ago by Jim Stichnoth

Status: newaccepted

comment:8 Changed 7 years ago by Jim Stichnoth

This is much the same issue as #10811, but even the latest ffmpeg sync in Master hasn't fixed it.

comment:9 Changed 7 years ago by Jim Stichnoth

This appears to be a problem with a heuristic mismatch between handbrake and ffmpeg. When the video does not have an explicit palette for the bitmap subtitle colors, ffmpeg tries to guess a reasonable palette, consisting of grayscale values evenly spaced between black and white.

Unfortunately, this guess does not match the apparent intent of the subtitle author, and the interior color ends up being gray instead of white, and the border ends up a combination of white and black instead of gray and black. (Between 0.25 and 0.26, ffmpeg reversed the order of guessed colors, resulting in the white and black being swapped, but the interior color is still gray.)

I don't know Handbrake, but the best option for now would be if you could convince Handbrake to produce explicit palette information.

I considered closing this ticket as an Upstream Bug, but I will wait until I can figure out how vlc gets it right.

comment:10 Changed 7 years ago by jens@…

The 'funny' thing is that the colors of the subtitles in mythtv playback ins't consistent. Sometimes they are as in the sample - pixelated/blurred colors and pixelated in grey, white and black. At other times they are yellow, orange and white and still pixelated.

In VLC all videos' subtitles are consistently black and white and not pixelated.

comment:11 in reply to:  10 Changed 7 years ago by Jim Stichnoth

Replying to jens@…:

The 'funny' thing is that the colors of the subtitles in mythtv playback ins't consistent. Sometimes they are as in the sample - pixelated/blurred colors and pixelated in grey, white and black. At other times they are yellow, orange and white and still pixelated.

In VLC all videos' subtitles are consistently black and white and not pixelated.

I would like to get a sample of a video with the yellow/orange/white subtitles, if possible. This suggests a problem mapping colors to an actual provided palette.

Note: See TracTickets for help on using tickets.