[FFmpeg-user] dvb teletext page number

[Marton Balint]

On Tue, 1 Dec 2015, Charles-Henri d'Adhémar wrote:

> Dear all,
>
> My video file is mpegts with 1 stream dvb teletext subtitle.
> The teletext subtitle contains 3 pages (see tag language below) for the same language (deaf people and more).
> There is a -txt_page option for the libzvbi-teletext decoder to specify the page number.
>
> How can I know which are the available -txt_page number to use, please ?
>
> I found a debug log with this info output during decoding
> https://github.com/FFmpeg/FFmpeg/blob/master/libavcodec/libzvbi-teletextdec.c#L297
> But this is definitely not what one would want to use programmatically.
> Maybe streams « extradata » have the information but I am not sure about how to extract the information from there (see ffprobe below).

Yes, extradata and the language metadata has this information.

For each language in the language metadata there are 2 bytes of binary 
information containing the teletext_type, the teletext_magazine_number and 
the teletext_page_number as they are in the Teletext descriptor 
specified in ETSI EN 300 468.

>            "extradata": "\n00000000: 0900 2888 1089                           ..(...\n",

Here

>            "tags": {
>                "language": "fre,fre,fre"
>            }

And here.

Regards,
Marton