Shown below are the speeds of the animations featured in the Sonic games. Such information can be used to replicate accurate animations in a fangame engine.
Every sprite subimage in this animation lasts for 24 frames. Sonic stays still for 288 frames (the subimage occurs 12 times in the animation code) before entering the waiting subimages of the idle animation. When the waiting portion begins, Sonic enters a subimage for 24 frames, then has his eyes wide open for 72 frames. Afterwards, he will alternate between two subimages every 24 frames, making Sonic appear to tap his foot on the ground. This will loop until the player takes action.
Every sprite subimage in this animation lasts for 6 frames. Sonic stays still for 180 frames (the subimage occurs 30 times in the animation code) before entering the first set of waiting subimages of the idle animation. He then blinks, which lasts for 6 frames, then has his eyes wide open for 30 frames. Afterwards, he will alternate between two subimages every 18 frames, making Sonic appear to tap his foot on the ground. This will loop until the player takes action.
Should the player NOT take action after Sonic taps his foot 4 times (144 frames), he will then look down at his wrist(watch?) for 60 frames, then resume tapping his foot. This foot-tapping/wristwatch sequence will continue 3 more times (204 frames/sequence*4=816 total frames). Afterwards, if no action is taken at this point, Sonic will enter a new animation where he lies down on the floor. It takes 6 frames for him to drop to the ground. He then enters a final alternating sequence tapping his finger against his shoe. Both subimages in this sequence last for 18 frames each.
Every sprite subimage in this animation lasts for 6 frames.
When Sonic is walking or running, the animation waits 8-absolute(Ground speed) frames before advancing to the next subimage. This is the same in Sonic 1, 2 and 3. This remains even when at full speed (spinning feet), or faster. Now, if the result of 8 minus the ground speed means it will wait less than one step before advancing a frame, it is just set to 1. So, to properly emulate this in your engine, here is some pseudo-code
//The frame-rate is set to 8 minus the absolute value of ground speed. frame_duration = max(8-abs(g_speed), 1); //Frame-rate minimum is capped at 1.
The spinning animation for jumping/rolling works slightly differently. The animation waits 5-absolute(ground speed) frames before advancing to the next subimage, instead of 8. When rolling along the ground, the speed of the animation will change with Sonic's ground speed. When rolling in the air or jumping, the animation speed will remain constant, due to the fact that ground speed does NOT update in the air. In other words, the animation remains the speed it was when you left the ground until you land.
The animation waits 32 frames before advancing to the next subimage when pushing. This remains true in all games.
While balancing, the animation waits 16 frames before advancing to the next subimage.
In Sonic 1, the animation waits 8 frames before advancing to the next subimage while braking. It will continue to loop between the two subimages until Sonic has stopped. In Sonic 2 and Sonic 3K, the animation will stop when it finishes, instead of looping.
The spindash has a frame duration of 1. And when you press the jump button it seems to reset.
For programs such as GameMaker or MMF, to display an animation properly without an advances system, you may need the speed of the animation instead of the duration of the frames.
//Converts the frame duration into an image_speed compatible value for Game Maker. image_speed = (1/frame_duration);