Playback of WTV files does not display DVB subtitles
Although VLC's "Video | Subtitles Track" displays an option "Track 1 - English" for a WTV file which contains a DVB subtitle stream, ticking that option does not cause the subtitles to be displayed.
In contrast, a TS file generated from the WTV file (eg open WTV in VideoRedo, save as TS) does display the subtitles in VLC when "Track 1 - English" is ticked.
Note that this is for DVB subtitles embedded in the WTV file, rather than a separate SRT subtitles file.
This behaviour has been confirmed with a variety of off-air standard def PAL (704x576x25) WTV files recorded by Windows Media Centre, though a thread on VideoLAN Forums http://forum.videolan.org/viewtopic.php?f=14&t=103864 shows that it has also been seen for NTSC WTV files as well.
Activity
Replying to [comment:1 jb]:
We need a sample.
Here are:
- 11-sec excerpt from WTV file recorded with Windows Media Centre, saved as WTV
- identical excerpt, saved as TS
VLC 2.0.7 displays subtitles on the TS but not the WTV
http://www.martinunderwood.f9.co.uk/mallard.wtv http://www.martinunderwood.f9.co.uk/mallard.ts
These are 704x576x25 MPEG2.
assigned to @fenrir
added Component::Demuxers label
I have reproduced this problem in VLC 2.1.5 for both Windows and Mac. The WTV file plays subtitles fine in Media Center (Windows7) but while VLC appears to detect the presence of the subtitles it will not display them. As per the original report these subtitles are DVB format which means they are bitmap subtitles embedded in the video stream, they are very similar therefore to DVD subtitles.
I can also say that a recording made by Elgato EyeTV of the same channel in the same MPEG2 video broadcast format with the same DVB subtitles does play correctly in VLC in that VLC is able to then display the DVB subtitles.
Since VLC can display the same DVB subtitles in a TS file and in my case an Elgato EyeTV recording which having checked with MediaInfo is also described as an MPEG Transport Stream format recording, it seems it is a problem not with handling DVB subtitles but with handling WTV muxed files.
As requested here is a link to a WTV file that has been tested as playing with DVB subtitles in Windows Media Center but fails to play the DVB subtitles in VLC. The recording is MPEG2.
See https://drive.google.com/file/d/0BwD4il5Z1G6fRWpqdWxHQXQ5aU0/edit?usp=sharing
I'm the original submitter of the bug - gosh, was it really 12 months ago?
I've just downloaded the sample file from the BBC News and as with the samples that I uploaded with the original bug, it plays perfectly but even when you select Subtitle | Sub Track | Track 1 - English, no subtitles are displayed. That's with VLC 2.1.5.
I downloaded VLC 3.0.0-git-20140718-1820 and this behaves exactly the same: it sees that subtitles are present and adds the Sub Track | Track 1 - English entry on the Subtitles menu, but it does not display them.
I translated the BBC News file from WTV to MPEG TS using VideoReDo. If I play that TS file in VLC 3.0.0, Subtitle | Sub Track | Track 1 - English causes the subtitles to be displayed. This was also the case for VLC 2.1.5 which was the last version I had installed before upgrading just now to 3.0.
Incidentally, the subtitles in this sample are slightly unconventional: they appear one word at a time rather than one screenful at a time. This is typical of a live broadcast which is subtitled in real time rather than a pre-recorded programme which is subtitled in advance of broadcast. I don't know whether that makes any difference with the way that VLC handles it. If you like I can upload a WTV file that has subtitles that appear one screenful at a time.
By the way, JB, you ask "will it crash in 3.0". The WTV file has not caused any version of VLC to crash - ie to end its execution prematurely.
Replying to [comment:9 martinu]:
I'm the original submitter of the bug - gosh, was it really 12 months ago? Incidentally, the subtitles in this sample are slightly unconventional: they appear one word at a time rather than one screenful at a time. yes, as in #10431 (closed) for ts files
See #9443 (closed)
jb: Is the root cause of the problem the same for DVB subtitles (the sample WTV files that I submitted) and for Closed Caption subtitles (as referred to in #9443 (closed))?
Incidentally I notice that VLC 2.1.5 fails to display the Closed Captions subtitles stream in the #9443 (closed) sample - it gives an error message 'VLC does not support the audio or video format "undf"' as soon as you tick Subtitle | Sub Track | Track 1. The Tools | Codec lists Stream 2 as being Type=subtitle, Codec=(undf).
In contrast, the same version of VLC gives no error message (but still does not display subtitles) with my DVB subtitles sample. Tools | Codec lists Type=subtitle, Codec=DVB Subtitles (dvbs).
So for DVB, VLC can at least identify the codec for the subtitle stream but not display it, whereas for CC it can't even find a codec for that stream.
Sorry to hurry you, but I think after 16 months from when I raised the bug I can ask this: any forecast for when/if you are going to fix the problem. Has anyone actually traced what the code is doing when it encounters a DVB stream in a WTV file. You said "we need to use the DVB decoder from libavcodec" - has that been tried yet and does it fix the problem? If so, will that be going into a released version of VLC?
Further to Comment 15, I've just tried with vlc-3.0.0-git-20141206-1135-win64.exe and the problem is still the same. The only difference from 2.1.5 is that vlc-3.0.0-git-20141206-1135 can identify the Codec for CC subtitles (#9443 (closed)) as being Type=Teletext (telx) and so it doesn't generate an error message when Subtitle | Sub Track | Track 1 is ticked.
But for both DVB and CC (telx) subtitles, nothing is displayed.
-
Replying to [comment:15 martinu]:
jb: Is the root cause of the problem the same for DVB subtitles (the sample WTV files that I submitted) and for Closed Caption subtitles (as referred to in #9443 (closed))?
Yes.
Sorry to hurry you, but I think after 16 months from when I raised the bug I can ask this: any forecast for when/if you are going to fix the problem.
No idea. WTV is a bastard format, with very little use outside of WMC recordings. We don't have our demuxer, but use libavformat for this, and it has a very bad API for subtitles, which explains our issues with both DVB and CC.
Replying to [comment:17 jb]:
Replying to [comment:15 martinu]:
jb: Is the root cause of the problem the same for DVB subtitles (the sample WTV files that I submitted) and for Closed Caption subtitles (as referred to in #9443 (closed))?
Yes.
Sorry to hurry you, but I think after 16 months from when I raised the bug I can ask this: any forecast for when/if you are going to fix the problem.
No idea. WTV is a bastard format, with very little use outside of WMC recordings. We don't have our demuxer, but use libavformat for this, and it has a very bad API for subtitles, which explains our issues with both DVB and CC.
As an experiment I have just tried a version of MPlayer with the same WTV file I posted earlier in this bug report. As MPlayer is the other major open-source media player I thought it would be a useful comparison.
It turns out that MPlayer - at least the version I used, can play DVB subtitles in WTV files. It is not perhaps as good as it should be due to whatever default outline/background/fill settings it defaults to using for bitmap subtitles but it does work. This suggests that using open-source libraries already in existence it should also be possible for VLC to achieve this. In fact I was under the impression VLC and MPlayer used much the same open-source libraries.
For the benefit of everyone the version of MPlayer I used is the one from here http://mplayerosx.ch/ i.e. MPlayer OS X Extended. It is version rev15 (1511) with "Official MPlayer SVN r36986" for the MPlayer binaries. This was then tested under Mac OS X 10.6.8.
My successful result with MPlayer implies that other projects like XBMC might also work, I don't currently have an XBMC setup to test this with. My own situation is that I use Windows Media Center to do TV recordings which of course produces WTV files, ultimately I would then like to be able to play them back via other computers/devices using VLC including potentially on an iPad.
