Recording of dvb_teletext does not stop until subtitles are available

[jakubvojacek]

Summary of the bug: When using ffmpeg to transcode portion of live stream that includes dvb_teletext, the ffmpeg does not stop until there are some data in the dvb_teletext stream. The dvb_teletext stream contains subtitle only like 50% of time and until some subtitles are available, it will keep the ffmpeg running. Below is a simple sample ffmpeg command that should record 10 seconds of stream.
How to reproduce:

time ffmpeg -y -txt_format text -txt_page 888 -i "udp://@239.100.200.2:1234?overrun_nonfatal=1&fifo_size=10000000" -map 0 -copyinkf -scodec mov_text -vcodec copy -acodec copy -t 10 -f mp4 test.mp4

The output of this command is

ffmpeg version 4.0-hd Copyright (c) 2000-2018 the FFmpeg developers
  built with gcc 6.3.0 (Debian 6.3.0-18+deb9u1) 20170516
  configuration: --cpu=native --enable-pthreads --extra-version=hd --enable-vaapi --enable-vdpau --enable-nonfree --enable-gpl --enable-swscale --enable-libx264 --enable-version3 --enable-nvenc --enable-libnpp --enable-cuda --enable-cuvid --enable-cuda-sdk --enable-filter=scale_cuda --enable-filter=thumbnail_cuda --extra-cflags=-I/usr/local/cuda-9.1/include --extra-ldflags=-L/usr/local/cuda-9.1/lib64 --enable-libx264 --enable-libx265 --enable-libxvid --enable-libass --enable-libwavpack --enable-libsoxr --enable-libfdk-aac --enable-libfreetype --enable-libmp3lame --enable-libopus --enable-libtheora --enable-libvorbis --enable-libvpx --enable-librtmp --enable-libnpp --enable-opengl --enable-version3 --enable-avresample --enable-avisynth --enable-openal --enable-opencl --enable-libzvbi --enable-iconv
  libavutil      56. 14.100 / 56. 14.100
  libavcodec     58. 18.100 / 58. 18.100
  libavformat    58. 12.100 / 58. 12.100
  libavdevice    58.  3.100 / 58.  3.100
  libavfilter     7. 16.100 /  7. 16.100
  libavresample   4.  0.  0 /  4.  0.  0
  libswscale      5.  1.100 /  5.  1.100
  libswresample   3.  1.100 /  3.  1.100
  libpostproc    55.  1.100 / 55.  1.100

Input #0, mpegts, from 'udp://@239.100.200.2:1234?overrun_nonfatal=1&fifo_size=10000000':
  Duration: N/A, start: 73177.274233, bitrate: N/A
  Program 1 
    Metadata:
      service_name    : Service01
      service_provider: FFmpeg
    Stream #0:0[0x100]: Video: h264 (Main) ([27][0][0][0] / 0x001B), yuv420p(progressive), 720x480 [SAR 40:33 DAR 20:11], 25 fps, 25 tbr, 90k tbn, 50 tbc
    Stream #0:1[0x101]: Video: h264 (Main) ([27][0][0][0] / 0x001B), yuv420p(progressive), 720x480 [SAR 40:33 DAR 20:11], 25 fps, 25 tbr, 90k tbn, 50 tbc
    Stream #0:2[0x102](cze): Audio: aac (LC) ([15][0][0][0] / 0x000F), 48000 Hz, stereo, fltp, 144 kb/s
    Stream #0:3[0x103](cze): Subtitle: dvb_teletext ([6][0][0][0] / 0x0006), 492x250
Output #0, mp4, to 'test.mp4':
  Metadata:
    encoder         : Lavf58.12.100
    Stream #0:0: Video: h264 (Main) (avc1 / 0x31637661), yuv420p(progressive), 720x480 [SAR 40:33 DAR 20:11], q=2-31, 25 fps, 25 tbr, 90k tbn, 90k tbc
    Stream #0:1: Video: h264 (Main) (avc1 / 0x31637661), yuv420p(progressive), 720x480 [SAR 40:33 DAR 20:11], q=2-31, 25 fps, 25 tbr, 90k tbn, 90k tbc
    Stream #0:2(cze): Audio: aac (LC) (mp4a / 0x6134706D), 48000 Hz, stereo, fltp, 144 kb/s
    Stream #0:3(cze): Subtitle: mov_text (tx3g / 0x67337874), 492x250
    Metadata:
      encoder         : Lavc58.18.100 mov_text
Stream mapping:
  Stream #0:0 -> #0:0 (copy)
  Stream #0:1 -> #0:1 (copy)
  Stream #0:2 -> #0:2 (copy)
  Stream #0:3 -> #0:3 (dvb_teletext (libzvbi_teletextdec) -> mov_text (native))
Press [q] to stop, [?] for help
frame=  250 fps=0.2 q=-1.0 Lq=-1.0 size=    1820kB time=00:00:09.98 bitrate=1493.7kbits/s speed=0.00774x    
video:1655kB audio:159kB subtitle:0kB other streams:0kB global headers:0kB muxing overhead: 0.366925%
Exiting normally, received signal 2.

real	21m34.743s
user	0m4.100s
sys	0m3.020s

While I was trying to record just 10 seconds, it kept on recording and would have kept waiting until some subtitles would be available. I have waited 21 minutes until I canceled it manually. When there are subtitles available at the time of transcoding, it does end on time (specified by the -t parameter)

I have tried to record the multicast using multicat into a file and process this file and it worked (didnt wait). Therefore it seems like it is only reproducible on live input.

Do you need any more information please?