Audio Buffers

Large: Prefer Non-Stuttering Karaoke
Large buffers, typically 1800 ms x 2, are used. Since the application keeps trying to preload audio data always for at least about 2 seconds (usually little less than 3.6 seconds), audio is less likely to stutter even when many video frames have to be dropped to maintain AV sync, due to heavy effects such as complicated karaoke, as long as the jump is less than about 2 seconds. For example, audio wouldn't stutter even if 40 frames at 24 fps (about 1.7 seconds) were dropped.
This enables you to have smooth-sounding preview of relatively complicated effects. Video frames may still be dropped more or less, but preview is not stuttering, Audio/Video/Sub in sync, and you can get a rough but good idea of your effects, real-time.
A down side is slow response time. The difference is rather subtle, but preview starts slightly less quickly. Response is especially bad when you are adjusting audio volume by moving the slider at the right bottom corner, or when you toggle on or off the mute button. This is because usually about 3-second audio data has been already sent to the device when you change the volume, and changes will only take effect after that time. However, you can stop (pause) preview quickly. Plus you shouldn't need to change audio volume often when typesetting. Smooth-sounding karaoke should be much more important for normal typesetters. This is the current default setting (since version
Small: Prefer Quick Response
Small buffers, typically 192 ms x 2, are used. This may work great for previewing ASS on AVI when ASS doesn't contain any complicated effects. In this setting, while the response is quick, heavy effects may cause audio stuttering if CPU power is not enough.
NOTE: When playback is only for a very short time, especially when you hit [F] or [A] (shortcut keys for playing only 0.5 seconds), always Small Buffers are used regardless of the current setting.
Medium: Prefer Neither
Medium-sized buffers, typically 600 ms x 2, are used. Response is not too bad, and smooth previewing is possible even when ASS contains somewhat complicated effects, but not as flexible as when Large Buffers are used. 10 frames @ 24 fps may be dropped without audio stuttering, but not 30 frames. This was the only one option in version and before.

Load ASS Quickly

Added in v0.1.1.5, 2009‒05‒02.

Not tested well. Currently this option works only with a Unicode file in UTF-16 LE (otherwise this option has no effect).

If enabled, the file loads a little faster—about 25% faster in some cases. Although the error check is less strict and you can only load an ASS that has normal end‐of‐line characters, this should not be a problem in most cases.

When enabled, you can also use the ;{*a3r::EOF} directive in your ASS. If your script has a line beginning with the 12 letters
all the lines (Dialogues, Comments, etc.) after it (including that line itself) are totally ignored and not sent to VSFilter. In other words, such a line is treated as the end of the file (EOF) in this mode. For example, you can skip a complicated karaoke Dialogues which would take a long time to load, by putting them at the end of your ASS file after the comment line ;{*a3r::EOF}. This may be especially useful when you do many small edits while previewing the results with Auto-Reload on Change (RoC), but you know you won’t change the karaoke part. In such a situation, the file may be reloaded more than 10 times faster. Once you disable the Load ASS Quickly option, the ;{*a3r::EOF} directive is ignored and the whole file is loaded again.

The Load ASS Quickly option works also with an ASS that does not have the ;{*a3r::EOF} directive. In that case the whole file is loaded normally, but somewhat faster, by assuming the file format is not unusual and skipping some special‐case handling. Unless your file is more or less complicated and takes a long time to load, the option may not be very useful.

2085 ms by Alt+Left/Right

Added in v0.1.1.13, 2010‒02‒10.

Unchecked (default): By hitting [Alt]+[Left Arrow] or [Alt]+[Right Arrow], you can seek the video back or forward by 50 frames. This behavior is compatible with VirtualDub AFAIK.

Checked: By hitting [Alt]+[Left Arrow] or [Alt]+[Right Arrow], you can seek the video back or forward by about 2085 milliseconds. If the frame rate is 24000/1001 fps or a similar value (such as 23.976 fps), this is exactly the same as seeking by 50 frames. In general, however, the result is quite different. For example, you'll seek 5 times as many frames (250 frames) in one go if the video is 120-fps. In some situation (for example, when you have to work with both a 24-fps video and the 120-fps version of the same video), this behavior may be more comfortable at least for a typesetter.

NOTE: Seeking by some shortcuts, such as [Alt]+[Shift]+[Left/Right], is always seek-by-time, while seeking by some other shortcuts, such as [Num+]/[Num-], is always seek-by-frames. There are a few other seeking methods, such as seek-by-Dialogues. See the items under the Navigate menu.