Go to
Menu > Options > Display.
Set Scaler to scales 4x3 or integer scales 4:3
Why do I write these walls of text?
Anyway, in
http://boards.openpandora.org/topic/6546-pcsx-rearmed-with-a-new-gpu/page-55#entry312828 I explained why 4:3 isn't good enough.
Interesting, on which game do you have the problem ? I've never seen that issue myself before.
On all of them. Remember that you have to set "Scaler" in [Display] to 1x1 in order to get the effect I'm talking about when using "Enhanced resolution". If you set it to 4:3 you actually override the built-in GPU plugin's pixel doubling, so yes - there is stretching everywhere, including MDECs, but it's also stretching to 4:3 (or a custom, absolute value), which is not what I want.
The fastest way to check it is I think with Final Fantasy Origins or Vagrant Story, because they switch resolution three times before they get in-game and have MDECs on the way. For example in FF Origins:
1. After running the ISO, the game starts in 320x240
2. After selecting FF1, an MDEC video starts in 320x240
3. After the video, FF1 itself starts in 256x240
"Hardware filter" set to none.
Using custom scaler and a resolution of 512x480:
1. Distorted image
2. Distorted image
3. Perfect scaling
Using 1x1 scaler and "Enhanced resolution":
1. Perfect scaling
2. No scaling at all (it's a bug, I think)
3. Perfect scaling
And, for comparison, using scaler set to 4:3 ("Enhanced resolution" is irrelevant here, because scaler overrides it):
1. Perfect scaling (since 320x240 is 4:3 to begin with)
2. Perfect scaling
3. Distorted image