#12 VSFilter Softsub ASS Wrong Shadow Alpha if Subs Overlapped

[Liisachan]

If ASS is muxed into MKV (softsubbed) and played back by VSFilter/MPC, when 2 subs overlap timing-wise, the 2nd-coming sub ("Ich..." in the example below) gets the wrong shadow alpha (4a); the 4a suddenly returns to normal when the 1st-coming sub ("Los!") disappears. Both older VSFilter and the newest version are affected.

(An example explained)
Style: style1,Verdana,50,
&H00ffeeff,&Hffffffff,&H00000000,&H80000000,
-1,0,0,0,100,100,0,0.00,1,1.00,10.00,2,20,20,20,0
Style: style2,Verdana,24,
&H0080ffff,&Hffffffff,&H80000000,&Hcc000000,
-1,0,0,0,100,100,0,0.00,1,0.75,1.50,8,2,2,8,0

;; Non-Overlapping
Dialogue: 0,0:00:01.00,0:00:03.00,style1,,0000,0000,0000,,Ich will spielen!

;; Overlapping
Dialogue: 0,0:00:05.00,0:00:09.00,style2,,0000,0000,0000,,Los!
Dialogue: 0,0:00:08.00,0:00:15.00,style1,,0000,0000,0000,,Ich will spielen!

The 1st "Ich...", not overlapped, shows correctly.
When the 2nd "Ich..." appears, its shadow is too thick.
When the "Los!" ends, the 2nd "Ich..." suddenly returns to normal.

A workaround is to divide the 1st-coming sub timing-wise:

Dialogue: 0,0:00:05.00,0:00:08.00,style2,,0000,0000,0000,,Los!
Dialogue: 0,0:00:08.00,0:00:09.00,style2,,0000,0000,0000,,Los!
Dialogue: 0,0:00:08.00,0:00:15.00,style1,,0000,0000,0000,,Ich will spielen!

Hardsub (TextSub) and an external ASS loaded to MPC, not muxed into MKV, don't have this problem.

[Liisachan]

Demo

[Liisachan]

ASS embedded

[Liisachan]

File Added: 4a_bug.ass

[Liisachan]

Workaround

[Liisachan]

File Added: 4a_bug_quickfix.ass

[Liisachan]

File Added: quickfix_samplex.mkv

[Liisachan]

workaround muxed into MKV for testing