ffprobe

• ffmpeg

Probe a DVD for 64 MBs or 60 seconds to check for VOBSUBs that hopefully show up by then:

dvd_copy -o - | ffprobe -probesize 67108864 -analyzeduration 60000000 -

Input #0, mpeg, from 'pipe:':
  Duration: N/A, start: 0.045500, bitrate: N/A
    Stream #0:0[0x1bf]: Data: dvd_nav_packet
    Stream #0:1[0x1e0]: Video: mpeg2video (Main), yuv420p(tv, progressive), 720x480 [SAR 32:27 DAR 16:9], 29.92 fps, 59.94 tbr, 90k tbn, 59.94 tbc
    Stream #0:2[0x82]: Audio: ac3, 48000 Hz, stereo, fltp, 192 kb/s
    Stream #0:3[0x81]: Audio: ac3, 48000 Hz, stereo, fltp, 192 kb/s
    Stream #0:4[0x80]: Audio: ac3, 48000 Hz, stereo, fltp, 192 kb/s
    Stream #0:5[0x21]: Subtitle: dvd_subtitle
    Stream #0:6[0x20]: Subtitle: dvd_subtitle
    Stream #0:7[0x23]: Subtitle: dvd_subtitle
    Stream #0:8[0x22]: Subtitle: dvd_subtitle