Playing DVB-T subtitles (S_DVBSUB)

Mikael Jepsen · 2011-05-11T23:14:04+00:00

Hi all, I'm using Dushmaniacs xbmc-pvr/tvheadend builds, but cannot get subtitles to show. I've tried vlc, xbmc and mplayer with no luck. Playing a live s...

Juha Ruotsalainen

Same problem here.

Andreas, could you shed some light on the subtitle format in a DVR Matroska file?

I'm planning on writing an app that would convert S_DVBSUB into S_IMAGE/BMP or S_VOBSUB. I would imagine those format would enable subtitles being shown in VLC/XBMC/whatnot. Then again, I may be imagining things...

--
jussi

Mikko Autio

This patch works with XBMC: http://pastebin.com/QnvgRqfp

- Mikko

Juha Ruotsalainen

Good call, Mikko!

This got me into looking at VLC's codebase: its Matroska demuxer code has a similar place where it checks for various streams and sets an interval VLC codec id based on that. Now, if I only had the time to try out tweaking VLC's code to add S_DVBSUB there...

Andreas Smas

Juha Ruotsalainen wrote:
> Same problem here.
>
> Andreas, could you shed some light on the subtitle format in a DVR Matroska file?
>

> I'm planning on writing an app that would convert S_DVBSUB into S_IMAGE/BMP or S_VOBSUB. I would imagine those format would enable subtitles being shown in VLC/XBMC/whatnot. Then again, I may be imagining things...

Yes, perhaps it would be even better to have Tvheadend do convertion to VOBSUB itself internally.

Or we could convince the developers of ffmpeg, vlc, etc to add support for DVBSUB in the code.

On all ffmpeg derivates (mplayer, xbmc, etc) it's just a one line patch as seen in this thread

>
> --

> jussi

Dennis Kurten

I recently started using ppa-pvr and tvheadend and ran into this same problem.

Subtitles (DVBSUB) work when watching live tv (which I suspect is on account of
the special HTSP code in "xbmc/cores/dvdplayer/DVDDemuxers/DVDDemuxHTSP.cpp")

but not from recorded matroska files.

Is it possible to manually convert the matroska back to a .ts and then extract the
subtitles with something like ProjectX? Nothing I've tried can make any sense of

the raw data extracted with mkvextract.

Also, I'd like to have a look at the patch Mikko supplied, but the link is down.

- Dennis

Mikael Jepsen

For reference, this is the one line patch Mikko supplied:


diff --git a/lib/ffmpeg/libavformat/matroska.c b/lib/ffmpeg/libavformat/matroska
index c7e9663..dd22ccd 100644
--- a/lib/ffmpeg/libavformat/matroska.c
+++ b/lib/ffmpeg/libavformat/matroska.c
@@ -59,6 +59,7 @@ const CodecTags ff_mkv_codec_tags[]={
     {"S_ASS"            , CODEC_ID_SSA},
     {"S_SSA"            , CODEC_ID_SSA},
     {"S_VOBSUB"         , CODEC_ID_DVD_SUBTITLE},
+    {"S_DVBSUB"         , CODEC_ID_DVB_SUBTITLE},
     {"S_HDMV/PGS"       , CODEC_ID_HDMV_PGS_SUBTITLE},
 
     {"V_DIRAC"          , CODEC_ID_DIRAC},

I considered requesting Dushmaniac to include the patch in xbmc-pvr, but if Andreas could make tvheadend convert it to VOBSUB, I guess that would be better (i.e. less need to convince a lot of other projects to the tvheadend way of putting subs in mkv). I'm not sure from Andreas' response if this is easy to do and/or could be done soon... If not, I guess a xbmc-pvr fix would be nice for the time being.

Dennis Kurten

Works like a charm, thank You!

Since it was this easy, I suppose that if ffmpeg only were to patch their code it would
propagate in a clean way to all projects that rely on that library.

Juha Ruotsalainen

Hi guys!

Just to make sure: are you using Lars Op dem Kamp's PPA as the source for the XBMC source code, or have you cloned the source code from github?

A side note: I reverted back to using VDR, since my time is limited, and in VDR subtitles work. But before that I recorded a whole bunch of Italian language course programs with tvheadend. I can say, that it's pretty tough trying to watch those without a hint of a subtitle :)

Mikael Jepsen

@Dennis: Yes indeed, however VLC for one does not use ffmpegs libavformat (they use their own demuxer), so they would not be fixed with this.

@Juha: Yes, I'm using Lars Op dem Kamp (aka. Dushmaniac)'s xbmc-pvr repo, but I guess either would be fine just for playing the files.

Dennis Kurten

Hello Juha,

I'm using the pvr-ppa branch from Lars' repo on github.

Hein Rigolo

tvheadend is one of the first programs to generate S_DVBSUB streams in a mkv, so that is why there is no widespread support for it yet.

Conversion of DVB subtitles to an other format is hard to do because DVB subtitles are not text but bitmaps. So any conversion would require OCR to convert the bitmaps back to text (ASCII). There are programs out there that can do this, but doing it "real-time" while writing the mkv could be difficult. An other drawback is that you loose information. One of the reasons that mkv was chosen as the file format for tvheadend was to contain as much as possible all the details of the program that was recorded, while also being able to add additional meta-data to the file. mkv is the only container format that allows for that at the moment.

Initially it was not possible to store the DVB subtitles into a mkv container. After some discussions with mkv developers on IRC it was decided that the S_DVBSUB stream would be added to the mkv as a separate track. At that time the tvheadend mkv muxer was the only program around that could do this.

Andreas was involved in a discussion with the MKV developers to get a S_DVBSUB correctly implemented in an mkv container (see this mailing list archive: http://lists.matroska.org/pipermail/matroska-devel/2011-February/thread.html#3948 ). Once this has been done, then others programs can use this format also. The VLC developers have also said that they would like to support the S_DVBSUB format.

I know of one other program that can use S_DVBSUB and that is a commercial program called VideoReDo.

Hein

Jaime Vazquez

Can someone help me understand how to apply the above patch to my xbmcbuntu installation? I've never done that before but would like to lean how. Thanks!