What is a difference between subtitling and teletext system in DVB?

D

deuxliquid

Member
My Satellite Setup
DVB-T, DVB-S
My Location
Hanoi
Hi everybody,
I am studying DVB standards and being confused in subtitling and teletext systems. Can anyone explain for me to understand clearly about them?
Thank you in advance!
Hai
 
Hi everybody,
I am studying DVB standards and being confused in subtitling and teletext systems. Can anyone explain for me to understand clearly about them?
Thank you in advance!
Hai
 
deuxliquid said:
Hi everybody,
I am studying DVB standards and being confused in subtitling and teletext systems. Can anyone explain for me to understand clearly about them?
Thank you in advance!
Hai
Click to expand...

Its quite easy. DVB has standarised to ways of transmitting subtitles. One possibility is to transmit subtitles via teletext of the TV channel. Then information is sendt to the receiver (teletext descriptor in PMT) which tells the recevier what teletext pages the different subtitles(languages) is carried on. Then the receiver decodes the ASCII character codes received and render fonts. In this system the fonts is generated by the receiver (or the manufacurer of the receiver). Many receivers has wery bad looking teltext style of fonts for subtitle.

Be aware that the teletext method for subtitles is by far the most common way of transmitting subtitles in DVB.

The other system called DVB subtitles transmit grapical objects just like a picture. This is transmitted on unique PIDs for the service. One PID pr. subtitle stream. The DVB subtitle is singalled with subtitle descriptor in the PMT for the service. The receiver must then receive this grapical objects from the subtitle PID and render the pixels. The broadcaster (TV channel) decides the fonts and location of the graphics. It is not possible to change fonts, location, size etc. as all graphics is preencoded by the broadcaster. This is the best method of transmitting subtitles as the quality of the subtitles can be just as good as proffesional equipment for in vision subtitles. Its used for all HDTV channels here in the nordics while all SD channels uses teletext subtitles (and some use in vision subtitles...).
 
deuxliquid said:
Hi everybody,
I am studying DVB standards and being confused in subtitling and teletext systems. Can anyone explain for me to understand clearly about them?
Thank you in advance!
Hai
Click to expand...

Its quite easy. DVB has standarised to ways of transmitting subtitles. One possibility is to transmit subtitles via teletext of the TV channel. Then information is sendt to the receiver (teletext descriptor in PMT) which tells the recevier what teletext pages the different subtitles(languages) is carried on. Then the receiver decodes the ASCII character codes received and render fonts. In this system the fonts is generated by the receiver (or the manufacurer of the receiver). Many receivers has wery bad looking teltext style of fonts for subtitle.

Be aware that the teletext method for subtitles is by far the most common way of transmitting subtitles in DVB.

The other system called DVB subtitles transmit grapical objects just like a picture. This is transmitted on unique PIDs for the service. One PID pr. subtitle stream. The DVB subtitle is singalled with subtitle descriptor in the PMT for the service. The receiver must then receive this grapical objects from the subtitle PID and render the pixels. The broadcaster (TV channel) decides the fonts and location of the graphics. It is not possible to change fonts, location, size etc. as all graphics is preencoded by the broadcaster. This is the best method of transmitting subtitles as the quality of the subtitles can be just as good as proffesional equipment for in vision subtitles. Its used for all HDTV channels here in the nordics while all SD channels uses teletext subtitles (and some use in vision subtitles...).
 
As far as I recall, teletext cannot be used within a DVB signal, owing to the lack of spare lines carrying information above the visible picture.

I believe digital text uses a separate transport stream, where the packets of information are dedicated to things other than video/audio.
 
As far as I recall, teletext cannot be used within a DVB signal, owing to the lack of spare lines carrying information above the visible picture.

I believe digital text uses a separate transport stream, where the packets of information are dedicated to things other than video/audio.
 
Channel Hopper said:
As far as I recall, teletext cannot be used within a DVB signal, owing to the lack of spare lines carrying information above the visible picture.

I believe digital text uses a separate transport stream, where the packets of information are dedicated to things other than video/audio.
Click to expand...

Teletext can be carried in a DVB transmission but as you correctly point out its not a part of the MPEG video. DVB is much more than video transmission :) DVB has made a huge numbers of specifications. Btw, DVB do not make any specifications for
video or audio compression even though the abbrivation means Digital Video Broadcasting. That kind of specs is made by ISO (MPEG specs).

One of the large number of DVB specifications specifies how to transmit teletext in a DVB transmission.

Teletext is encoded and deliverd on a PID (stream) seperate from video. The same ting is done with DVB subtitles but its a different DVB spec for that.

All DVB specs is downloadable for free from www.etsi.org
 
Channel Hopper said:
As far as I recall, teletext cannot be used within a DVB signal, owing to the lack of spare lines carrying information above the visible picture.

I believe digital text uses a separate transport stream, where the packets of information are dedicated to things other than video/audio.
Click to expand...

Teletext can be carried in a DVB transmission but as you correctly point out its not a part of the MPEG video. DVB is much more than video transmission :) DVB has made a huge numbers of specifications. Btw, DVB do not make any specifications for
video or audio compression even though the abbrivation means Digital Video Broadcasting. That kind of specs is made by ISO (MPEG specs).

One of the large number of DVB specifications specifies how to transmit teletext in a DVB transmission.

Teletext is encoded and deliverd on a PID (stream) seperate from video. The same ting is done with DVB subtitles but its a different DVB spec for that.

All DVB specs is downloadable for free from www.etsi.org
 
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