resizing and hardsubbing

[mog08]

I've just started to use AviSynth. There are 26 anime episodes that are in MKV format, dual audio with SSA sub files. I'd like to add the soft subs to the video, take the original audio (japanese), re-encode to mp4 or avi format.

Question 1. directShowSource. how do you take an audio stream from MKV that is not default? I know the long way around by extracting the audio file. But Avs doesn't handle AAC tracks. so I create a new MKV with mkvMergeGui.

Question 2. vsfilter.dll & lanczos4resize. I also want to resize the original video's dimention (720,480) to 320x214. but i discovered that if i apply the textSub("c:\xxx\xxx.ass") after lanczos4resize(320,214), the subtitles would become weird in the preview. Why is this? If i apply textSub before the resize, it would be fine. while not knowing why, i also did another unrelated video clip resizing and hardsubbing, from (704,396) to 640x360. applied textSub after lanczos4resize and it turned out really well.

Question 3. lanczos4resize & vsfilter.dll. After 8 episodes (720,480), the original MKV video's dimention changed to 640x480. I did some test, and it seemed that 720x480 looked more natural. so I went like this:
lanczos4resize(720,480)
textSub("c:\xxx\xxx.ass")
lanczos4resize(320,214)

I originally attempted this:
directshowsource("c:\xxx\xxx.mkv") # is 640x480
textSub("c:\xxx\xxx.ass")
lanczos4resize(320,214)
But the subtitles were slightly out of proportion.

the question is this, should i go with the following order instead?
directshowsource("c:\xxx\xxx.mkv") # is 640x480
lanczos4resize(640,428)
textSub("c:\xxx\xxx.ass")
lanczos4resize(320,214)

Question 4, are there more crucial/commonly used filters that work differently depending on the order?

Thanks.

[foxyshadis]

SSA and ASS subtitles are sometimes highly dependant on the dimensions of the video, depending on how complex they are, and they're always somewhat dependant. SRT are totally independant. So no, always apply your subtitles before you change the display dimensions in any way.

In the second set, you're also changing the AR, so it's no wonder it looks weird. The whole video should look weird! Resize to 320x240 instead.