I have created two sample video clips which illustrate various problems in Enigma2’s current DVB subtitling implementation. Both video clips, and the actual ’bug report’ (which is actually supplied in the form of a colorful timecode table at the bottom of that page) are available here:

• Common DVB subtitling defects in Enigma2

The following picture is a sample frame from a montage video clip featured on that page. It compares the DVB subtitle rendering support in Enigma2 to some other sources. (Disregard that you may not know the language used in the subtitles and you may already spot one of the typical glitches that occur quite constantly in DVB subtitles rendered by Enigma2.)

Zitat

Originally posted by Gruffy
it seems like the DVB PES packets arrive VERY late some times and in this case I will have to drop them as their PTS has been passed. The strange thing with this is that I have a recording and this is behaving differently when I playback it. Some times, the text is OK and some not. [...] I have traced this back to that my (PES) filters does not receive the data properly and to me it seems as the driver is buffering my PES packets too much some times so that it is taking too long for them to pop out in my filter.

Interesting. It did not occur to me to me that playing back the same .ts recording several times in a row could yield different results. I have not tried that yet, but I’m now wondering whether that would also be the case for the built-in DVB subtitling support in Enigma 2. It should be tested at the earliest opportunity. (That would have to be done by someone else, though, as I don’t have a physical access to the DM 7025 for the next two weeks or so.)

If someone would like to give it a try, the above-mentioned web site of mine contains an ideal test clip (243 MB) for this purpose: a 10-minute .ts capture of a German police detective show with Finnish DVB subtitles. One just needs to select the Finnish DVB subtitles from the subtitle menu at the beginning of the playback. An analog video capture device would be useful as that allows capturing the test runs and running an easy side-by-side comparison. AviSynth will come handy as well – that’s what I used for creating the original three-panel montage clip.

Actually, I could post the AviSynth script which I originally used for combining the captures on a single screen:

vid_h=DirectShowSource("mod-humax.avi",audio=false,pixel_type="RGB24",fps=25).Crop(9,0,-9,0)
vid_a=DirectShowSource("mod-analog.avi",audio=false,pixel_type="RGB24",fps=25).Crop(9,0,-9,0)
vid_d=DirectShowSource("mod-dm7025.avi",audio=false,pixel_type="RGB24",fps=25).Crop(9,0,-9,0)


vid_h=BicubicResize(vid_h,316,259).Crop(0,2,0,-1).Subtitle("Humax F4-FTA", x=10, y=5)
vid_a=BicubicResize(vid_a,316,259).Crop(0,2,0,-1).Subtitle("YLE TV2 (Analog PAL)", x=10, y=5)
vid_d=BicubicResize(vid_d,316,259).Crop(0,2,0,-1).Subtitle("Dreambox DM 7025", x=10, y=5)


vid_b=BlankClip(width=316, height=256, pixel_type="RGB24", length=15567, color=$000000)
vid_b=ShowSMPTE(vid_b, x=160, y=30, fps=25, text_color=$ffffff)


vid_top = StackHorizontal(vid_d,vid_h)
vid_bot = StackHorizontal(vid_b,vid_a)


StackVertical(vid_top, vid_bot)
AddBorders(44,32,44,32)
AssumeFPS(25)

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Please let me know if I can help you trace this in any way.

I would like to take this opportunity to thank you for your work on the 2SUB plugin – it’s much appreciated on this side of the Gulf.

The following can mostly be ignored as far as Enigma 2 and its built-in DVB subtitling support is concerned, but for your information, some bug reports about the 2SUB plugin as well:

• For some reason or the other, 2SUB 2.06 – when used with an official Enigma 2 v2.2 image – does not seem to erase the previous DVB subtitle panel at all. Instead, it leaves it hanging on the screen until a new panel comes along. (If there are silent passages in a tv show, the previous text panel will be stuck on the screen indefinitely until something is said and a new panel replaces it.)
  

  
  

• Another weird thing is that Teletext subtitles work fine with live broadcasts, but 2SUB cannot seem to pick them up from recordings (again, with a standard Enigma 2 v2.2.) Is this a known issue?

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Originally posted by Gruffy
I will see if can get some time to investigate the file and see if 2SUB logging can reveal some new clues to this problem.

That would be nice. I don’t think there are too many people around who would have a good technical grasp on how DVB subtitles work, so any pair of experienced eyeballs (such as yours) would potentially be very valuable in helping to solve the problem.

Zitat

About the mentioned bugs for 2SUB...I have not gotten any of those reports, but...I have also been very busy with other things so I could have missed it in some way.

I’ve seen the 2SUB “hanging DVB subtitles” problem mentioned a couple of times on Finnish forums (here, for example) but I don’t know if anyone has reported it back to you.

If you haven’t seen any such problems yourself, my working theory is that perhaps there is enough leeway in the DVB subtitling standard that it allows broadcasters do things a bit differently from one country to the other.

In other words, the Finnish YLE – which is currently the only broadcaster in Finland using DVB subtitles on all their channels, and, subsequently, the only broadcaster whose broadcasts I’ve been able to test a) with the 2SUB plugin and b) with Enigma2’s built-in DVB subtitling support (and from whose broadcasts the sample clips linked to this thread have been captured) – might be doing something a bit different way than, e.g., the broadcasters local to you. This is just pure speculation on my part as I have not done any analysis on the actual streams, but a similar thing was already found to be true with the other Enigma2 bug report which I recently filed!

Since both the 2SUB plugin and the built-in DVB subtitling support in Enigma2 show partly similar traits – namely, 1) that the text is left hanging on the screen for a long time, and 2) that there are no natural gaps in the subtitle display between two consecutive subtitle panels (in places where such gap is displayed in the analog simulcast and by other set-top boxes on the market) – this could certainly be a case where the broadcaster is perhaps interpreting and using some aspect of the DVB subtitling standard in an unexpected (but yet not necessarily non-standard) way. (Standards are [too] often like that – open to interpretation in some little details.)

One reason for not getting too many bug reports from Finland might be that many Finnish Dreambox owners seem to prefer 2SUB/gSUB and the Teletext subtitles over the DVB subtitles. The reason for this preference is quite simple: Teletext subtitling – when available – allows the viewer to set the font, the size of the font, and positioning to their liking.¹) It’s also the path of least resistance at this moment since the Teletext subtitling support in 2SUB does not suffer from the “hanging text” problem.

YLE, however, does not give any guarantees about continuing to simulcast the Teletext subtitles in the future. DVB subtitling is their “official” subtitling format, and Teletext subtitles are only broadcast for the time being, for compatibility reasons – and that service is not really even publicly advertised anywhere. So a time might come when they will finally pull the plug on the Teletext subtitles once and for all...

¹) OK, limited scaling and positioning support could be done for DVB subtitles as well – at least when allowing some broadcaster-specific heuristics and assumptions – but I have never seen that implemented anywhere. It woud be a nice feature, though!

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I will see if I can get any time to look at this some day...at the moment I am trying to spend the small time I have on other things than 2SUB and gSUB....

Yes, I noticed you have recently closed down the blog where you used to report gSUB/2SUB-related developments.

If you don’t have the time for further development – for the time being, at least – how about open-sourcing the project so that others could help, or even take over? It would be a real shame to see all that good work go in vain, or to be left in an unmaintained state.

As it stands now, with the current (built-in) Enigma2 DVB subtitling support being... ahem... in its early days, 2SUB is a very valuable addition to the DM 7025 user experience in all the subtitling-crazy countries.

Zitat

Originally posted by Jukka Aho

Interesting. It did not occur to me to me that playing back the same .ts recording several times in a row could yield different results. I have not tried that yet, but I’m now wondering whether that would also be the case for the built-in DVB subtitling support in Enigma 2.

I just put this theory to test today by playing back the original sample clip (243 MB) several times in a row in Enigma2 – with the built-in DVB subtitling support enabled – and recapturing the decoded/rendered video + subtitles to the computer from the analog video outputs of the DM 7025 for further analysis.

As far as I can tell, everything – including those subtitle panels that have obvious rendering errors (as per the timecode table) – was rendered identically in each test run. I would take that as a proof that it’s a systematic problem in Enigma2’s subtitle decoding/rendering algorithm and not something that would only occur semi-randomly due to buffering/demuxing problems.