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dvbtextsubs

NAME

dvbtextsubs - extract subtitles stored as teletext-pages in an MPEG-file.

SYNOPSIS

   dvbtextsubs [OPTIONS] pid pageno < recording.ts > subtitles.xml
 
 

DESCRIPTION

DVB broadcasts can include subtitles encoded in the teletext pages sent together with the video and audio in the MPEG transport stream. The teletext pages are sent on a separate pid and the subtitles are identified by their own pagenumber within the teletext stream. dvbtextsubs can extract the subtitles from within the MPEG transport stream and output it in either an xml-based format suitable for processing with xml2spumux or in Subviewer format that can be read by most software video-players.

dvbtextsubs takes two mandatory parameters. The first parameter is the pid for the teletext-stream in the input-file. The second parameter is the teletext pagenumber where the subtitles can be found. See the section FINDING PID AND PAGENUMBER below for more information. If no options are passed to dvbtextsubs, the subtitles will be output in xml-format on standard out.

Supported stream formats

dvbtextsubs expects to receive a stream in MPEG-TS format on standard in. The stream does not have to contain any PAT or PMT, only the teletext pid is necessary (and an audio-pid if the -apts option is used).

Options

The following options can be passed to dvbtextsubs:

-srt

Output data in Subviewer format.

-pts <offset>

Adjust each timestamp for the subtitles by adding <offset> milliseconds.

-apts

Ignore the timestamp on the teletext stream and use the timestamp of the audio-stream for the subtitles instead.

-apid <pid>

Use pid <pid> as the audio-pid to synchronize the subtitles to. This option is only valid together with the -apts option. Normally, dvbtextsubs should be able to auto-detect the audio-pid.

-keeppts

Normally, dvbtextsubs outputs timestamps as an offset to the start of the MPEG stream. -keeppts tells dvbtextsubs to use the absolute value of the pts-field (Presentation Time-Stamp) instead.

FINDING PID AND PAGENUMBER

Information on which pid and pagenumber the subtitles can be found in is normally stored in the PMT (Program Map Table) inside the MPEG stream. One way to retrieve this information is to use ``dvbtune -i'' to dump the PAT and PMT to xml-format. A channel with teletext subtitles contains an entry like this (indentation added for clarity:

   <stream type="6" pid="1244">
     <teletext tag="0x56">
       <teletext_info lang="swe" type="1" page="100"/>
       <teletext_info lang="swe" type="2" page="694"/>
       <teletext_info lang="swe" type="5" page="794"/>
     </teletext>
   </stream>
 
 

In this example, the teletext is sent with pid 1244 and the subtitles are sent on page 694 (type=2).

EXAMPLES

To extract the teletext subtitles from a recorded TS-stream containing an audio-pid, a video-pid and the subtitles on pid 1024, page 692, use

dvbtextsubs 1024 692 < recording.ts > subtitles.xml

The generated xml-file is suitable for feeding to xml2spumux

To extract the teletext subtitles from the same file in a format suitable for displaying with xine, use

dvbtextsubs -srt 1024 692 < recording.ts > recording.srt

The file recording.srt will contain timestamps that are relative to the start of the file.

If you want to play the file in mplayer instead, use

dvbtextsubs -keeppts -srt -1024 692 < recording.ts > recording.srt

This time the timestamps will be relative to the Presentation Timestamp in the MPEG-TS file.

If the subtitles are not properly synchronized with the audio and video, it may be because the Presentation Timestamp for the teletext stream is different from the Presentation Timestamp for the audio/video. Try using the -apts and -apid options described above. They instruct dvbtextsubs to use the relative position of the teletext page in the stream as the timestamp rather than the PTS for the teletext stream.

SEE ALSO

xml2spumux, dvbsubs

AUTHOR

dvbtextsubs was written by Dave Chapman <dave -at- dchapman /dot/ com>. The latest version is available from http://www.linuxstb.org/dvbtextsubs/.

This manual page was written by Mattias Holmlund, <mattias -at- holmlund /dot/ se>