And specially while moving a keyframe

(oops this is Bug 589818)

*** Bug 589818 has been marked as a duplicate of this bug. ***

Pretty much the same issue. If the tooltip is shown at all times, well, update it in realtime when dragging. If it's shown only on hover, also update it in realtime when dragging.

I don't think that persistent tooltips would be useful whereas it would clutterint the GUI.
Showing them on hover should be enough

The easiest way to implement this is to show the labels for all keyframes, but only while either dragging or when the cursor is hovering over the curve as a whole. I can filter it so that it only shows the one closest to the mouse with a little extra effort. 

In either case, what units should I use? Percentages or the native value for the property?

I think your behavior suggestion would make sense.

As for units, what are examples of "native values"? In most case, aren't native values percentages anyway? The only example I can think of so far is decibels in the case of audio. In any case, I think it would make sense to use the "native values" since most of those are percentages anyway.

The 'native' value would just be an unformatted int or float value, and interpreting it would therefore be up to the user. If you prefer to think of volume as a percentage, I can insert code in there to display it as a value between 0% and "200%"

Well if it is not a "meaningful" value like decibels, or if the unit is not displayed, I would surely prefer percentages.

even for audio : decibels is meaningless for me
It's easier to work with percentages

okay let me try this again: the 'native' value for the volume element is a floating point number between 0 and 2 (really 10, but you want me to limit it to 2). Should I or should I not bother to multiply this by 100, drop the decimals, and add a % sign? Or would you prefer to see the floating point value rounded to some arbitrary number of decimal places (whatever fits comfortably on the screen).

I bring this up because doing this 'properly' involves adding a mechanism to the property interface that tells the UI how the value should be formatted.

Yes, it may be harder to implement, but I think it would be worth it. Especially if we need to have specialized labels in the future (for example, panning: "30% left", "11% right"?)

take a look at the bug_589814 branch in my repository. Any feedback would be appreciated.

So far so good (there's only keyframes for volume anyway). However, I would suggest
- making the text black on white instead of red on white, which is a bit harder to read
- giving a little bit more padding around the text (so that the bubble is bigger), again for better legibility/contrast with the surroundings

I have updated my branch. Keyframe values are no longer clipped to the bounds of the clip. Would like feedback on the changes. Looking in Jeff's direction.

As discussed on IRC, it all seems fine to me, good work! My only nitpick is that the white rounded rectangle behind the percentage is a bit too small; when you have three digits, the % sign gets out of the rectangle boundaries. Maybe add a few pixels all around to improve legibility.

commit 262b0844cad0ad42d061ac0b1356b8bd8150b1fd
Author: Brandon Lewis <brandon_lewis@alum.berkeley.edu>
Date:   Mon Feb 1 15:10:05 2010 -0800

    curve.py: checkpoint: fixed bug 589814