I've discovered the method used by FFmpeg to assign maps, and it seems that it could easily be
improved and that it's potentially a big deal.
My specimens are VOBs, reported by FFprobe.
For VTS_02_1.VOB, FFmpeg assigns streams as follows:
Stream #0:0[0x1bf]: Data: dvd_nav_packet
Stream #0:1[0x1e0]: Video: ...etc.
Stream #0:2[0x83]: Audio: ac3, 48000 Hz, 5.1(side), fltp, 448 kb/s ...5.1
isolated score
Stream #0:3[0x82]: Audio: ac3, 48000 Hz, stereo, fltp, 192 kb/s ...2.0
commentary
Stream #0:4[0x81]: Audio: ac3, 48000 Hz, 5.1(side), fltp, 448 kb/s ...5.1
dialog
Stream #0:5[0x80]: Audio: ac3, 48000 Hz, stereo, fltp, 192 kb/s ...2.0
dialog
For VTS_02_2.VOB, FFmpeg assigns streams as follows:
Stream #0:0[0x81]: Audio: ac3, 48000 Hz, 5.1(side), fltp, 448 kb/s ...5.1
dialog
Stream #0:1[0x1e0]: Video: ...etc.
Stream #0:2[0x82]: Audio: ac3, 48000 Hz, stereo, fltp, 192 kb/s ...2.0
commentary
Stream #0:3[0x80]: Audio: ac3, 48000 Hz, stereo, fltp, 192 kb/s ...2.0
dialog
Stream #0:4[0x83]: Audio: ac3, 48000 Hz, 5.1(side), fltp, 448 kb/s ...5.1
isolated score
Stream #0:5[0x1bf]: Data: dvd_nav_packet
Question: Does this make any sense at all?
Further Investigation. The summary below easily shows the audio streams 'move'
between maps.
VTS_02_1.VOB map VTS_02_2.VOB map actual stream IDs
2.0 dialog a:3 a:2 0x80
5.1 dialog a:2 a:0 0x81
2.0 commentary a:1 a:1 0x82
5.1 isolated score a:0 a:3 0x83
Confirmed: That FFmpeg's maps are not assigned by audio stream IDs, but are assigned in the order in
which they are first encountered.
That is not the least bit sensible.
The following would make sense.
VTS_02_1.VOB map VTS_02_2.VOB map actual stream IDs
2.0 dialog a:0 a:0 0x80
5.1 dialog a:1 a:1 0x81
2.0 commentary a:2 a:2 0x82
5.1 isolated score a:3 a:3 0x83
Can this be corrected?
--Mark.
--
Met-a-verse:
While I was going up the stair,
I met-a man who wasn't there.
He wasn't there again today.
I wish, I wish he'd go away.
-- "IDENTITY", 2003, Columbia Pictures
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