2009-11-14.

From a set of video DVD images, the `playability' falls into two groups, 
and these groups correspond perfectly to whether the `file' command
calls the files UDF or ISO-9660:
	UDF filesystem data (version 1.5)
	ISO 9660 CD-ROM filesystem data UDF filesystem data (unknown version, id 'NSR0

Several players cope happily with either, e.g. xine.
But mplayer is most important to me, as the purpose is to convert these
files to much smaller (H.264 + oggvorbis) in Matroska, and I use 
mencoder and mplayer for pretty much all the work in doing this.
I've never had troubles before, so these must be pretty unusual 
images to get, apparently re-encoded by someone else en route.

mplayer plays the udf files as (for example):
	mplayer -dvd-device file.iso  dvd://2

but it fails on the iso9660 files, giving this sort of message:
	Playing dvd://2.
	libdvdread: Using libdvdcss version 1.2.10 for DVD access
	libdvdnav:DVDOpenFileUDF:UDFFindFile /VIDEO_TS/VIDEO_TS.IFO failed
	libdvdnav:DVDOpenFileUDF:UDFFindFile /VIDEO_TS/VIDEO_TS.BUP failed
	libdvdread: Can't open file VIDEO_TS.IFO.
	Can't open VMG info!
	No stream found to handle url dvd://2
which makes it seem pretty likely it wanted UDF structure ...

if, on the other hand, the file is played directly as a video file,
	mplayer file.iso
then the iso9660 ones work, BUT of course there is then lots of 
menu and warning junk at the beginning; it presumably is playing 
all tracks together in sequence,

and if the file is mounted first, then the mount-point is used as the 
source, it used to work:
	mount -t iso9660 -o loop,ro file.iso /mnt/iso	
	mplayer -dvd-device /mnt/iso  dvd://2

but note the past tense: the latest batch of images, together with my 
system after its several-year-step upgrade, gives:
	Playing dvd://2.
	libdvdread: Using libdvdcss version 1.2.10 for DVD access
	libdvdread: Attempting to use device /dev/loop0 mounted on /mnt/iso for CSS authentication
	libdvdnav:DVDOpenFileUDF:UDFFindFile /VIDEO_TS/VIDEO_TS.IFO failed
	libdvdnav:DVDOpenFileUDF:UDFFindFile /VIDEO_TS/VIDEO_TS.BUP failed
	libdvdread: Can't open file VIDEO_TS.IFO.
	Can't open VMG info!
	No stream found to handle url dvd://2
just as for the plain image (above), though now making it clear that it's
trying to use the image (/dev/loop0; the block-device access to the image)
rather than just the mount-point.

Well, it was a little tedious even in the past to coordinate eight parallel jobs of 
mounting images rather than just accessing them directly; also, the latest system
is more arkward about user mounts of files through loop devices: having mounted
/vid/img on /mnt/img by the fstab line including 'loop', the attempted umount in 
the latest gentoo refuses, saying that as it's /dev/loopN, not the original /vid/img,
that's mounted, it won't do it (mtab disagrees with fstab), so one then has to 
create the loop device manually by losetup /dev/loop0 /vid/img 
(after chown /dev/loop[0-9]) and mount that (from fstab), then umount and 
losetup -d /dev/loop0: all rather less fun to bother putting in the scripts that get 
set up for a batch of recodings ... we seek a better way.

Why not try converting the files from the iso9660 image to a udf structure?
Fix the problem at source.  
First try (failed) was to create empty files a little larger than the image, 
make a (default) udf filesystem on them, copy the iso9660 files across, then 
hope that was ok. 
	for f in *.iso ; 
 	do
		s=`ls -l $f | awk '{ print $5 }'`
		S=$((s+100000000)); 
	  	dd if=/dev/zero of=../$f bs=1 count=0 seek=$S
		losetup /dev/loop1 ../$f
	  	mkudffs /dev/loop1
		mount -t udf -o rw /dev/loop1 U
		mount -t iso9660 -o ro,loop $f I
		cp -Rv I/* U/
		umount I
		umount U
		losetup -d /dev/loop1
	done

This failed to play, and was not even recognised by `file'.

A little searching gave this:
	http://web.archive.org/web/200/http://dvd.chevelless230.com/index.html
(via http://ubuntuforums.org/showthread.php?p=1789415).

Following the prescription there, but ignoring the claims of how important 
permissions are (why? just that they saw these ones?), yet including the 
AUDIO_TS directory `just in case',  THIS WORKED:
	mkdir U D
	mkdir D/AUDIO_TS D/VIDEO_TS
	for f in *.iso
	do
		mount -t iso9660 -o loop,ro $f U
		echo "$f"
		ls -lR U
		mount --bind U/VIDEO_TS D/VIDEO_TS
		mkisofs -dvd-video -o ../$f D/
		umount D/VIDEO_TS/
		umount U
	done
of course, if any DVD had contained AUDIO_TS then it should have been 
used directly without the bind mount; but none did.

So (cutting the very long story very short), a DVD video image needs to be 
a particular form of UDF filesystem, apparently even with a particular 
ordering of files: cdrtools' mkisofs can do this:
	mkisofs -dvd-video -o outfile.iso image_directory/