G'day Daniel, I just came up with a couple more ideas thatcould be worth mentioning, that you can keep in mind for thefuture...
On Fri, 23 Jan 2009, BOUWSMA Barry wrote:
> The other output format is `pids', and here's that from> back in 2006, before the use of the second audio channel> on the german broadcasters became widespread (last year):> > ZDF (0x6d66) 01: PCR == V V 0x006e A 0x0078 \> (deu) 0x0079 (2ch) TT 0x0082 AC3 0x007d> > Here PID 0x79 is tagged as `2ch' (it's NAR for the Beeb),> and covers both audiodescription and occasional original-> language (mostly english language) broadcasts without> overdubbing. This was before DVB subtitles were introduced.> > Oh, here's an old BBC `pids' output, also including subtitles:> > BBC 1 London (0x189d) 01: PCR == V V 0x1388 A 0x1389 \> (eng) 0x138a (NAR) TT 0x138b SUB 0x138c
Now, I want to mention in detail the TT (teletext) and SUB(subtitle) services, at least, how they are implemented inthis part of europe -- other parts of the world will likelybe different, but my purpose is to throw around ideas in thehope that something will stick to the ceiling and be interestingand possibly useful.
I mentioned that I find the nearly 100% penetration of subtitlesto be quite useful to me personally, although it and in-fieldsigning are intended for people whose hearing is not so goodas mine, but whose vision is intact.
The subtitles are sent in both a selected teletext page, aswell as a separate DVB-subtitle stream. Unfortunately, thesupport that `mplayer' has for DVB subtitles last I knew, is,well, bad to none, and basically requires completely rewritingthat bit. `xine' worked better some months ago, but at thattime had some timing problems.
Anyway, as I understand it, DVB subtitles are sent as bitmaps,which unfortunately makes it difficult for you to use them.This also explains the difference in appearance between theBBC subtitles and those of ITV. However, I haven't seenmangled fonts due to transmission errors, while I have seenincorrect yet properly-formed characters at times. So myunderstanding of DVB subtitles is far from complete or correct.
Standard teletext, as was introduced with analogue transmissionsas part of the vertical blanking interval, has been carriedover to DVB broadcasts. In the case of the BBC, this is mostlylimited to subtitles on page 888, while the german services I'vementioned offer full text services, occasionally includingsubtitles, but on a limited set of programmes. Only the ZDFhas both teletext and DVB subtitles at present, of the germanpublic broadcasters. These DVB subtitle fonts again differ inappearance from any of the british public broadcasters.
In the UK, the move has been away from conventional teletextwith the introduction of digital services, replacing it withan MHEG-based service. In germany, there has been a push tosupplement regular teletext with an MHP-based service, but forlack of interest and readily-available hardware, this haspretty much died out or stagnated.
I seem to recall that in Australia, use is made of an MHEGservice. I don't know if a regular teletext service isavailable -- you will see this in the results, when you havea tuner capable of scanning.
Now, ideally, a teletext service, being text-based, can betrivially converted to braille or spoken. I'm not sure aboutthe MHEG services, as they seem to place more importance onthe on-screen appearance, yet they do use a TrueType font.
Anyway, while conventional teletext is not simple ASCII-like,it is based on a hamming of a limited character set which canbe converted back to a standard 128- or 256-character setfont, and of course the normal characters can be displayed asbraille.
Now, here is an example of some of the useful informationto be found on a full teletext service, to show that, if itwere available to you, you might find it interesting. Thisis a page giving inter-bank exchange rates from the Euro toyour own currency, and is meant as an example (it's in german,but should be trivial to understand)
/GIP IG*** PHOENIX Mi 21.01.09 18:01:45 PHOENIX.text 2/2 Devisenkurse Letzte Datenabfrage Diff. Kurs- 21.01.09, 18:00 Uhr Vortag zeit
USA....... (USD) 1,2857 -0,20% 17:59 GB........ (GBP) 0,9369 +0,94% 17:59 Schweiz... (CHF) 1,4767 -0,13% 17:59 Japan..... (JPY) 112,9800 -2,35% 17:59
Kanada.... (CAD) 1,6365 +0,37% 17:59 Südafrika. (ZAR) 13,0970 -1,05% 17:50 Hongkong.. (HKD) 9,9990 +0,07% 17:49 Singapur.. (SGD) 1,9401 -0,13% 17:50 Australien (AUD) 1,9804 -0,23% 17:59 Neuseeland (NZD) 2,4637 -0,78% 17:49 Indien.... (INR) 63,3633 +0,36% 17:49 China..... (CNY) 8,8013 +0,03% 17:15 Mexiko.... (MXN) 17,9189 -0,85% 17:49 Argentin.. (ARS) 4,4618 +0,33% 17:16 Brasilien. (BRL) 3,0380 -0,73% 17:54
Sortenkurse ->
(reproduced without permission, sorry)
Unfortunately, relatively few programmes are sent with anysubtitles, and I'm having to dig deeply in my snapshots ofteletext pages to find an example I can show, instead of // X G*** PHOENIX Mi 21.01.09 18:01:38 KEINE UNTERTITEL(no subtitles)
More unfortunately, I've just verified that my utility is notrecognizing and writing to disk the subtitles that are currentlybeing broadcast on page 150 by one particular broadcaster, so it's back to the coding for me... Meaning, I can't paste an example here.
However, my point is that if this type of service is broadcastin your area, you may find it interesting and useful, as youwould be able to make use of the text content within.
Just an idea which I had...
By the way, I don't know how foreign non-english-language filmswould be handled by your broadcasters. In general, the text-based subtitles are not sent when there are on-screen subtitles,for example, when the BBC screens a film in its native languageand subtitles. That means that, for example, the film ``LolaRennt'' was sent out with the primary audio channel containingthe original german, and no teletext subtitles, with thetranslation into english appearing as part of the videosignal, meaning that you can't make use of it, nor could youmake use of the audio (if you understand german, then substitutefrench, portuguese, japanese, or some other language which hasbeen broadcast as original-with-subtitles). Other broadcasterstend to dub everything of serious commercial value into thenative language with the same limited number of voice talent,so the issue of original audio versus subtitles doesn't come up.The cultural channel `arte' is somewhat an exception, where viathe different satellite positions you might find dubbed german,dubbed french, and original english, subtitles in french orgerman, or original language broadcasts in the `trash' seriesof cinematic gems with on-screen subtitles in either french orgerman, keeping out those audience members unable to understandthe original and unable to see the on-screen subtitles...
barry bouwsma
_______________________________________________linux-dvb users mailing listFor V4L/DVB development, please use instead linux-media@xxxxxxxxxxxxxxxxxxxxxxxx@linuxtv.orghttp://www.linuxtv.org/cgi-bin/mailman/listinfo/linux-dvb
