[FFmpeg-user] Decklink SDI Closed Captions / teletext capture

[Ross Currie]

Has anyone had any success capturing closed captions text from SDI using a
decklink card?

I'm having trouble getting any data from the subtitles stream.

I'm trying a command like this:

ffmpeg -txt_format text -raw_format yuv422p10 -format_code ntsc
-teletext_lines all -video_input  sdi -f decklink -i 'DeckLink Mini
Recorder (2)' -y test.vtt


ffmpeg version N-88685-g81c021c Copyright (c) 2000-2017 the FFmpeg
developers
  built with gcc 4.8 (Ubuntu 4.8.4-2ubuntu1~14.04.3)
  configuration: --prefix=/root/ffmpeg_build --pkg-config-flags=--static
--extra-cflags=-I/root/ffmpeg_build/include
--extra-ldflags=-L/root/ffmpeg_build/lib --bindir=/root/bin --enable-gpl
--enable-libass --enable-libfdk-aac --enable-libfreetype
--enable-libmp3lame --enable-libtheora --enable-libvorbis --enable-libx264
--enable-openssl --enable-nonfree --enable-decklink --enable-libzvbi
  libavutil      56.  0.100 / 56.  0.100
  libavcodec     58.  1.100 / 58.  1.100
  libavformat    58.  2.100 / 58.  2.100
  libavdevice    58.  0.100 / 58.  0.100
  libavfilter     7.  0.101 /  7.  0.101
  libswscale      5.  0.101 /  5.  0.101
  libswresample   3.  0.101 /  3.  0.101
  libpostproc    55.  0.100 / 55.  0.100
[decklink @ 0x3194700] Found Decklink mode 720 x 486 with rate 29.97(i)
Guessed Channel Layout for Input Stream #0.0 : stereo
Input #0, decklink, from 'DeckLink Mini Recorder (2)':
  Duration: N/A, start: 0.000000, bitrate: 225261 kb/s
    Stream #0:0: Audio: pcm_s16le, 48000 Hz, stereo, s16, 1536 kb/s
    Stream #0:1: Video: v210 (V210 / 0x30313256), yuv422p10le(bottom
first), 720x486, 223725 kb/s, 29.97 fps, 29.97 tbr, 1000k tbn, 1000k tbc
    Stream #0:2: Subtitle: dvb_teletext
Output #0, webvtt, to 'test.vtt':
  Metadata:
    encoder         : Lavf58.2.100
    Stream #0:0: Subtitle: webvtt
    Metadata:
      encoder         : Lavc58.1.100 webvtt
Stream mapping:
  Stream #0:2 -> #0:0 (dvb_teletext (libzvbi_teletextdec) -> webvtt
(native))
Press [q] to stop, [?] for help
size=       0kB time=00:00:00.00 bitrate=N/A speed=   0x
video:0kB audio:0kB subtitle:0kB other streams:0kB global headers:0kB
muxing overhead: unknown
Input file #0 (DeckLink Mini Recorder (2)):
  Input stream #0:0 (audio): 1498 packets read (9596784 bytes);
  Input stream #0:1 (video): 1499 packets read (1398746880 bytes);
  Input stream #0:2 (subtitle): 0 packets read (0 bytes); 0 frames decoded;
  Total: 2997 packets (1408343664 bytes) demuxed
Output file #0 (test.vtt):
  Output stream #0:0 (subtitle): 0 frames encoded; 0 packets muxed (0
bytes);
  Total: 0 packets (0 bytes) muxed
Output file is empty, nothing was encoded (check -ss / -t / -frames
parameters if used)


a/v capture works fine but I always get " Input stream #0:2 (subtitle): 0
packets read (0 bytes); 0 frames decoded; "

I have confirmed my source has captions by connecting it to a TV and
turning them on/off via the TV controls.

Any help would be appreciated.
My goal is to get a live stream of the decoded captions text from my SDI
source.