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Diffstat (limited to 'TROUBLESHOOTING')
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diff --git a/TROUBLESHOOTING b/TROUBLESHOOTING new file mode 100644 index 0000000..062becd --- /dev/null +++ b/TROUBLESHOOTING @@ -0,0 +1,244 @@ + +Ttxtsubs is made to be fully automatic with no other user settable +settings than preferred subtitling language or languages and a few +appearance options. This is how set top boxes work, and, in my +opinion, how these things should work. Users should not have to know +anything about PIDs, encodings or other strange information as in this +case teletext page numbers. + +Sadly, some channels do not provide the information necessary for +automatic subtitle decoders to do it's work, and some do but do it +wrong. There has also been bugs in ttxtsubs that made it incorrectly +parse the information it gets, I of course hope those are gone by now. + +If you think there are subtitles on a channel but ttxtsubs doesn't +show them, you may want to read the text below. + + +Troubleshooting ttxtsubs +------------------------ + +A good thing to check first is how another set top box behaves. If the +other set top box automatically finds and displays teletext subtitles +while ttxtsubs don't, there is probably a problem in ttxtsubs. If the +channel in question is a French, please see the French channel problem +section below. + +If neither the set top box nor ttxtsubs automatically finds the +subtitles but you can get them by manually entering the teletext page +number for them on your TV set or your DVB decoder, chances are that +the subtitles aren't announced in the channel's "service information", +at least not correctly. You can double check this using dvbsnoop, see +below. + + +To find the subtitles, a DVB receiver as ttxtsubs scans the channel's +"Service Information". This meta data contains information about what +PIDs to use for receiving the channel, such as what PID to use for +video and what audio PID should be used for what language. VDR 1.3 and +up uses the Service Information for automatic video and audio PID +setup just as a typical set top box does. + +For teletext with or without subtitles, the Service Information +contains information about what PID and what teletext page to use for +what language and purpose. A typical set of information for a channel +with Norwegian and Swedish teletext with subtitles could look like +this: + PID Language Teletext Page Purpose + 4711 nor 200 Initial page for teletext browsing + 4711 nor 299 Subtitles + 4711 nor 298 Subtitles for hearing impaired + 4711 swe 300 Initial page for teletext browsing + 4711 swe 399 Subtitles + 4711 swe 398 Subtitles for hearing impaired +In this case, a receiver set up for Norwegian subtitles for hearing +impaired would use PID 4711 and teletext page 298 for subtitles. If +the user pushes the button for interactive teletext information +browsing, the set top box should start with presenting page 200 which +is supposed to be an index page in Norwegian. +Note that the PID may be different for each language and purpose. This +is one reason why ttxtsubs has to find out the PID itself and doesn't +care at all about how you set up the channel's TPid. + + +To find out what ttxtsubs is doing, you must currently (0.0.5pre2) +look at the stderr output in the shell where you run VDR. In a future +version, it may instead show this in the VDR menus in a more user +friendly manner. At the end of this text you can find some typical +messages from ttxtsubs with explanations. + + +You can use dvbsnoop, http://dvbsnoop.sourceforge.net, to check what +the service information really says. +First dump pid 0 to find the Program Map PID for your channel: + $ dvbsnoop -n 1 0 +and get for example: + Program_number: 5060 (0x13c4) + reserved: 7 (0x07) + Program_map_PID: 5060 (0x13c4) +The entry you are looking for is the one with a Program_number the +same as the Sid number in VDR. +If you don't know the program number, you can dump pid 17 and +look for the channel name you want and get the Service_id number: + $ dvbsnoop -n 1 17 +You may need to do this several times to find your channel (or use a +number larger than 1 after -n). +In this case the program map PID is the same as the Program Number. + +When you know the program map PID, dump it: + $ dvbsnoop -n 1 5060 +and look for + DVB-DescriptorTag: 86 (0x56) [= teletext_descriptor] +Again, you may need to do this several times to find this information +(or use a number larger than 1 after -n). +On a well behaved channel with teletext subtitles you should see +something like this: +... + Elementary_PID: 1024 (0x0400) +... + DVB-DescriptorTag: 86 (0x56) [= teletext_descriptor] + Descriptor_length: 30 (0x1e) + ISO639_language_code: swe + Teletext_type: 1 (0x01) [= initial teletext page] + Teletext_magazine_number: 1 (0x01) + Teletext_page_number: 0 (0x00) + + ISO639_language_code: swe + Teletext_type: 2 (0x02) [= teletext subtitle page] + Teletext_magazine_number: 6 (0x06) + Teletext_page_number: 146 (0x92) + + ISO639_language_code: swe + Teletext_type: 5 (0x05) [= teletext subtitle page for hearing impaired people] + Teletext_magazine_number: 7 (0x07) + Teletext_page_number: 146 (0x92) +.... +This is the information that a DVB decoder uses to find the +subtitles. If you find a DVB-DescriptorTag of 69 (0x45) = +VBI_data_descriptor or 70 (0x46) = VBI_teletext_descriptor that you +think could point out the subtitles, please contact the +author. Ttxtsubs currently doesn't decode those as I have never seen +them, but it is probably easy to implement. If there is no information +for subtitles but there are subtitles in the teletext stream, please +ask the TV company to fix it, see next section. + + +If you want to watch a channel that has teletext subtitles but the +subtitles aren't announced in the Service Information, contact the TV +company and ask them to correct this. If you politely inform them +about the problem, they may very well correct it. After all, it is in +their interrest to have satisfied viewers. Don't take "you will have +to enter the subtitles page number on your TV set" as an answer - this +is just to sad an user experience and is not how it is supposed to +work with DVB. Try to convince them that this is what you and the +standard and the viewers want. Here is a template for such a letter: +----- +Sirs, + +Your TV channel [CHANNEL NAME] that can be found on DVB +[Satellite/Cable network/Terrestrial network] [SATELLITE POS/NETWORK +NAME] with video PID [NNN], audio PID [NNN] and teletext PID [NNN] has +teletext subtitles on page[s] [NNN[, NNN...]]. Sadly, the DVB service +information for your channel does not announce the subtitles, so my +DVB receiver can not find them and display them. + +I hereby ask you to update your channel's service information to +also announce the existence of the subtitles. Since your service +information already announce the existence of the teletext PID, only a +small addition is needed to also announce the teletext subtitle +page[s]. + +For further information about the service information descriptor that +is needed, please see the standard document ETSI EN 300 468, paragraph +6.2.40. You can download this document for free from www.etsi.org. + +By sending a teletext subtitles descriptor according to this +specification, my and other decoders that are using it will be able to +automatically pick them up and present the subtitles to the viewer. +----- + + +There is a known problem with some French channels. Because of some +old specification interpretation mistake, some channels send the +teletext page number in decimal coded as binary, and not as the +standard says in hexadecimal. Since there are set top boxes sold that +has the same bug so that they can work with there channels, they are +reluctant to correct this. The service information for those channels +typically say that the subtitles are on page 858 or 859 when they +really are on page 888 or 889. To still be able to use those channels, +you can in ttxtsubs turn on the "Workaround for some French chns" +option which will remap numbers in the X5Y range into X8Y. Since this +would also remap the page number for a channel that really is using +for example page 859, this is an option that is off by default. If +you see this problem, please contact the channel provider and make +them understand that time will only make it harder to correct this +mistake as more decoders with this bug will be out there and software +updates for older set top boxes will be harder and harder to get. +Some channels do what they can to gradually correct this by sending +both a descriptor for French subtitles on page 859 (whish is +interpreted as page 889 on the old non standard decoders), and as +French for the Hearing Impaired on page 889 which is the setting that +can be used on standard compliant decoders. +(For the technically interrested: The hundreds figure is in teletext +called "magazine" and is sent separately from the 8 bit "page +number". Each magazine can actually have up to 256 pages and the page +number is really in hex, but only the 100 pages which use only the +figures 0-9 are normally seen by the user as only those numbers can be +entered on the remote control keyboard. 59 hex is 89 decimal, and here +is where something went wrong.) + + +Note that some channels don't use teletext subtitles but instead use +DVB subtitles, which is something different. DVB subtitles are sent as +bitmaps, somewhat like DVD subtitles. You can find a plugin for DVB +subtitles here: http://www.saunalahti.fi/~opvirtan/vdr/subtitles/ + + +Typical ttxtsubs messages and explanations +------------------------------------------ + +===== +ttxtsubs: Found selected subtitles on PID 1024, page 792 +----- +The subtitles for the language that you have selected is at teletext +page 792 on teletext PID 1024. + +===== +ttxtsubs: Found non HI subtitles on PID 976, page 199 +----- +You have selected subtitles for the hearing impaired, but on this +channel there are no such subtitles. Ttxtsubs uses the non hearing +impaired subtitles for the selected language instead. + +===== +ttxtsubs: Wanted subtitle language(s) not found on channel, available languages: + 889: fra (Subtitles) +----- +Subtitles for the language you have selected is not available on this +channel, but there are other alternatives, in this case French. + +===== +ttxtsubs: Wanted subtitle language(s) not found on channel, available languages: + 100: swe (Initial Page (The teletext start page, not a subtitles page!)) +----- +This means that there is a start page for interactive teletext +browsing announced, but no subtitles. There may still be subtitles in +the teletext stream, but ttxtsubs won't find them since they are not +announced correctly. If so, double check that this is the case and +then contact the TV company, see above. + +===== +ttxtsubs: No teletext subtitles on channel. +----- +No teletext stream at all was announced for this channel. + +===== +ttxtsubs: Service Information read: timeout! +----- +No Service Information data could be found for 250 ms (a quarter of a +second). This could be an indication of bad reception, but may also be +because the cards tuner, a motorized antenna or a LNB hasn't yet +settled for the new channel. Ttxtsubs will retry for up to 10 +seconds. Ttxtsubs will cache whatever it finally finds out about the +channel, so you will only see this happening at the most once for each +channel and vdr run. |