Specifically, Channel 4 assigns the data to different stream numbers: one programme might have the mpeg2video on
Stream #0:5, and the dvb_subtitle on
Stream #0:8, and the very next programme on
Stream #0:1 and
Stream #0:4 respectively.
OK, so most people won’t understand, and even fewer care. 🙂
I have a dongle (EyeTV, very nice) that records broadcast Freeview onto my old Mac (quite old, late 2006, but it ain’t broke, so doesn’t need fixing). And I end up with the raw broadcast mpeg file on the machine. Now I want to be able to move it elsewhere, and also compress it somewhat (MPEG-2 is not great compression).
I can simply tell EyeTV to export the video, and it will, although it takes a while to process (remember, 1.66 GHz Core Duo 🙂 ). Or I could even just move the mpeg file and use VLC to view it.
But I like to have the subtitles.
Now, perhaps surprisingly, the subtitles on broadcast TV are not text – they are images! So the only thing to do is overlay the images on the movie.
Of course, when it comes to this sort of thing, FFMPEG is your friend
-filter_complex "[0:5][0:8]overlay", I finally worked out. But you will see that I need to know which streams to overlay. And the bastards keep changing them. And I don’t have a utility that will identify them (and FFMPEG doesn’t, as far as I can tell.)
This used to be a problem for BBC & ITV too, but now I have Get iPlayer Automator, which downloads those nicely for me.