keyframe every frame about collada-exporter HOT 2 CLOSED

That's just how the exporter works, a keyframe is generated for every frame on the global timeline. This has to happen as the exporter exports only linearly interpolated animations but Blender is capable of quadratic/Bezier/wave... animation curves. So the timeline has to be oversampled otherwise for e.g. a sinewave animation curve would turn into an abrupt sawtooth curve.
If you want to expert only 9 frames then work with a 9 frame timeline and adjust the playback speed. E.g. cut out the 3 unused between frames and reduce playback speed to 25%.

from collada-exporter.

Indeed, this is done by design when the animation curve isn't linear (see the above comment).

from collada-exporter.