From Aegisub Manual
A small collection of Frequently Asked Questions about Aegisub - mostly stuff that didn't fit anywhere else.
 Karaoke effects?
See the Karaoke Templater tutorials.
 Can I create DVD subtitles with Aegisub?
Not directly, but there's a nifty program called MaestroSBT that can convert SSA to VOBSubs. It does have quite a bunch of restrictions on what tags and other things may be used, so reading its manual first is advised. Also note that it does not accept ASS - only SSA. You can use Aegisub's File -> Export... dialog to save real SSA files.
 Does Aegisub allow saving to SRT?
Yes, but only if it means that no information will be lost. In other words, if you have any override tags that aren't \1c, \b, or \i, Aegisub won't allow saving directly to SRT. However, you can still export to SRT by using the File -> Export... dialog box. Just uncheck all the checkboxes (clean script info, VFR transform etc.).
 What's this PRS stuff?
Pre-Rendered Subtitles. Basically a way to "encode" ASS (text) subtitles into pictures, which can then be encoded into the video using an Avisynth filter. There's also a DirectShow renderer, but it's in early development and not ready for public use yet. PRS has a few advantages over ASS (and a few disadvantages too). One advantage is that it doesn't require much CPU power to render onto the video - all the effort is spent when "encoding" to PRS. Another is that the subtitles will look exactly as the one who rendered them intended, which is not guaranteed with ASS (not even when rendering with VSFilter, as it has had, and still has, quite a few rendering bugs). The main disadvantage is that PRS takes more space than ASS and other text-based subtitle formats do.
 I've found a bug!?
Report it on the bug tracker. Please include as many details as possible in your report! Remember that if a bug is not on the bug tracker, it does not exist as far as we are concerned.
 Why doesn't Aegisub have <feature X>? <Program Y> has it!
Quite possibly because we didn't know you wanted it. Request it on the bug tracker and see what happens.
 Where can I find more information and/or get help?
For Aegisub-related stuff, the forums and the IRC channel are good places to ask questions. The Aegisub wiki also contains some more obscure information not included in the manual for various reasons, and so does the forums. For general video-related questions, Doom9.org and its forums is generally the place to go.
 I click the "Play video" button, and the video and audio aren't synchronized at all!
That's not a question.
But anyway, this is because of the way Aegisub displays video, it does not guarantee sync with the audio at all. Also, sometimes AviSynth can be quite slow at delivering frames, which would make real sync playback impossible. The "play video" feature is intended to display frames in rapid succession to check that some typesetting looks right, not as a replacement for a media player application. You can be sure that, if it sounds right when you click the "play line" button for the audio, and the subtitle looks like it's at the right frames, it is timed correctly to the audio and it is timed correctly to the video. If you don't believe this, just test it in a real media player (or hardsub it) and see for yourself.
If you absolutely must have this, feel free to implement it yourself.
 Are there any VSFilter bugs I should know about?
In one word: yes.