Xvid4PSP - MKV - Sub

[Vsion]

Hi everyone!!
I'm trying to burn the subtitles on MKV file (h264+AC3) with Xvid4PSP but i have, one single problem:
why the output file is smaller than the input?
Here are my configuration:
- input file is Video: MPEG4 Video (H264) 720x480 (169:96) 29.97fps Audio: Dolby AC3 48000Hz stereo {from MPC}
- use different resize filter, different video encoding

I need to burn subtitles on video, not resize or other things. Audio is in copy.
Is it possible? I need to change program?

Thank you!!

[txporter]

Did you go to the Video Menu and then Resolution/Aspect and make sure it was set up how you want it? I believe that XVID4PSP will by default do some cropping (at least in left/right dimensions) and will resize to square pixels from anamorphic. What is the resolution on the output file?

[Baldrick]

Smaller file size or video resolution/size?

[Vsion]

Txporter: The resolution of the output file needs to be the same. But i solve. I forced the option aspect video to 720*480 and 1:1.
Baldrick: i mean resolution.

I solve it, but the output file is without sound. I use Copy for it. If i open it with MKVMerge it is only with video track. Subs is now ok.
Fortunally, I extract the audio track from the original file and merge it.

Sorry for delay but I was busy at work.
Thanks!