[FFmpeg-user] dvb teletext page number

[Charles-Henri d'Adhémar]

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).

Thank you very much in advance for your help !
Cheers,
CH.


ffprobe -print_format json -show_data -show_streams -select_streams s mymovie.m2ts | python -m son.tool
fprobe version 2.8.3 Copyright (c) 2007-2015 the FFmpeg developers
  built with gcc 5.2.0 (GCC)
  configuration: --prefix=/usr --disable-debug --disable-static --disable-stripping --enable-avisynth --enable-avresample --enable-fontconfig --enable-gnutls --enable-gpl --enable-ladspa --enable-libass --enable-libbluray --enable-libdcadec --enable-libfreetype --enable-libfribidi --enable-libgsm --enable-libmodplug --enable-libmp3lame --enable-libopencore_amrnb --enable-libopencore_amrwb --enable-libopenjpeg --enable-libopus --enable-libpulse --enable-libschroedinger --enable-libsoxr --enable-libspeex --enable-libssh --enable-libtheora --enable-libv4l2 --enable-libvidstab --enable-libvorbis --enable-libvpx --enable-libwebp --enable-libx264 --enable-libx265 --enable-libxvid --enable-shared --enable-version3 --enable-x11grab --enable-nonfree --enable-libfdk-aac --enable-libzvbi
  libavutil      54. 31.100 / 54. 31.100
  libavcodec     56. 60.100 / 56. 60.100
  libavformat    56. 40.101 / 56. 40.101
  libavdevice    56.  4.100 / 56.  4.100
  libavfilter     5. 40.101 /  5. 40.101
  libavresample   2.  1.  0 /  2.  1.  0
  libswscale      3.  1.101 /  3.  1.101
  libswresample   1.  2.101 /  1.  2.101
  libpostproc    53.  3.100 / 53.  3.100
{
    "streams": [
        {
            "index": 4,
            "codec_name": "libzvbi_teletextdec",
            "codec_long_name": "Libzvbi DVB teletext decoder",
            "codec_type": "subtitle",
            "codec_time_base": "1/90000",
            "codec_tag_string": "[6][0][0][0]",
            "codec_tag": "0x0006",
            "width": 492,
            "height": 250,
            "id": "0x155",
            "r_frame_rate": "0/0",
            "avg_frame_rate": "0/0",
            "time_base": "1/90000",
            "start_pts": 5735141496,
            "start_time": "63723.794400",
            "duration_ts": 647953135,
            "duration": "7199.479278",
            "extradata": "\n00000000: 0900 2888 1089                           ..(...\n",
            "disposition": {
                "default": 0,
                "dub": 0,
                "original": 0,
                "comment": 0,
                "lyrics": 0,
                "karaoke": 0,
                "forced": 0,
                "hearing_impaired": 0,
                "visual_impaired": 0,
                "clean_effects": 0,
                "attached_pic": 0
            },
            "tags": {
                "language": "fre,fre,fre"
            }
        }
    ]
}