It turns out that at least one video in Starship Titanic, for the
Lift Indicator, has only a single transparency frame in track 2.
The added code, therefore, when it doesn't find an index entry
for the desired frame number, works backwards until it finds a valid
frame (likely frame 0), and then scans forward. If it hits the end
of the video, then it simply uses whatever last frame it last decoded.
This is needed for Starship Titanic, where videos can have a secondary
video track. It was simpler to use the callback as a means to select
one video track each across two decoders than trying to make VideoDecoder
and/or AVIDecoder support decoding from multiple video tracks simultaneously
Starship Titanic in particular needs this, since some of the videos
have extra junk at the end of the file, such as ycursors.avi,
and parsing fails if we don't respect the filesize field
In SSCI, VMD is drawn by a standard CelObjMem wrapped by a
ScreenItem, giving the location of the bitmap memory to the
decoder. The decoder already supports this, but the API was
previously hidden behind the AdvancedVMDDecoder wrapper
(which is more convenient to use than the VMDDecoder class).
We don't support playing videos with multiple edits backwards. Taking the code
path to move to the next edit when playing backwards sets the current edit index
to an invalid value with the video still trying to play. Which results in out of
bounds reads, and ultimately a crash.
This fixes multiple crashes in Myst. Using the key without the chest on
Stoneship, resetting the clock tower puzzle, and using the switch in the trees
in Channelwood.
This was a regression introduced in a59f5db505ffce9567c3bc8adf30d2f843910d65.
If seeking to the final frame of an edit, _nextFrameStartTime wouldn't be adjust properly and would wrongly say that it's at the end of the edit. This never affected anything because of the edit "-1" hack.
Relying on the videos to have 'initial frames' for audio tracks is not the best way to handle AVI videos. Now videos without initial frames (or broken interleaving) will buffer properly.
