[DVDnav-discuss] dvdnav patches from handbrake project

[Alexander Roalter]

On 05/29/2010 02:52 AM, John Stebbins wrote:
> 
> * nav-forward-seek.patch
> This patch guarantees that a request to seek forward always results in
> the new position being moved forward.
> libdvdnav has a problem in that it is difficult to gracefully recover
> from a read error and continue on to subsequent blocks on the disc.  An
> application would like to seek forward past the current block after
> getting a read error in order to attempt to get past the bad block(s).
> But dvdnav_sector_search() does not guarantee that a requested forward
> seek will actually move the current position forward.  It truncates down
> to the nearest VOBU which will almost always cause a forward seek
> request by a single block (or a small number of blocks) to move the
> current position backward.  This behaviour puts the application into a
> loop of: read failure, attempted forward seek (which results in backward
> seek), read failure ...
> 

I have found this behavior to be a major nuisance, seeking forward on
certain positions always seeks nearer and nearer to a specific position
in a certain chapter, there's no way of seeking beyond this position
with the 10-seconds skip, skipping by a minute mostly works (but at
times also not) and 10 minutes forward is simply too much.


Just a question in the mean time: did someone else experience audio
playback glitches on chapter breaks with dvdnav? This seems to have gone
with current SVN.

I have though one DVD (German "The Producers", sadly with Sony copy
protection) that creates a working dumpstream, but played directly from
disk starts the picture from a wrong position, and on every seek jumps
back to this position (audio is ok, though). I can deliver more
information on that if desired.

Another DVD (German "Transformers 2", with a different copy protection)
plays OK (with the aforementioned seek problems). There mplayer crashes
at the menu (which I don't care about), but still has major problems
stitching together the chapters, which are not contiguous on disk
(apparently, on this disk the same main feature is present around 30
times, almost each time with a different program chain, if I understand
correctly). On such chapter breaks, where there is need to seek to a
different position, I get

[ac3 @ 0xd97660]frame sync errort: -0.100   4/  4 ??% ??% ??,?% 0 0
[ac3 @ 0xd97660]incomplete frame:  0.495 457/457 11%  0%  3.4% 0 0
[ac3 @ 0xd97660]frame sync error:  0.499   0/  0 ??% ??% ??,?% 0 0

with an audible (and visible, some block artifacts) glitch.

I assume the same will be valid also for DVDs with normal seamless
branching, where also jumps are required... All the Alien (1-4) special
editions come to mind with that, I still have to confirm this.

To go back to the Transformers DVD, dumpstream seeks to a different
position than the non-dumpstream playback.




-- 
Cheers,
Alex