RS - Example: Predefined Values

In the next example we want to calculate the retiming curve's keys from already given values. This workflow is essential if you have to synchronize a simulation with other footage. Here are the “hard” facts:

Frame f @ 25 f/s	0 f → 32 f	32 f → 86 f	86 f → 141 f	141 f → 184 f
Speed factor	normal speed	0.25	2.30	normal speed

In the first step, the frames are converted into seconds, because it is more precise to work with this unit, but you can use frames for the retimed simulation as well. The term “normal speed” means that the playback factor is exactly 1.0. In order to get a frame's corresponding time in seconds, it has to be divided by the frame rate:

Time [s] = Frame [f] / Frame rate [f/s]

It is also always a good idea to calculate the original lengths of the time segments, since these values will be the basis for all our considerations. So, the converted table is now:

Time [s]	0 s → 1.33 s	1.33 s → 3.58 s	3.58 s → 5.64 s	5.64 s → 7.36 s
Original length [s]	1.33	2.25	2.06	1.72
Speed factor	1.0	0.25	2.30	1.0

The entries under “Time [s]” represent the curve's Y values (vertical axis). What you have to do now is to calculate the corresponding retimed X values (horizontal axis). For this step, a calculation rule is required:

Retimed length [s] = Original length [s] / Time factor

Now the second table from above can be extended with the following line:

Retimed length [s]	1.33 s	9.00 s	0.90 s	1.72 s

The next task is to recalculate the end points for each segment – the results define the curve's X values. To get these values you have to reuse the previously calculated end points:

Calculation	0 s + 1.33 s	1.33 s + 9.00 s	10.33 s + 0.90 s	11.23 s + 1.72 s
End points [s]	1.33 s	10.33 s	11.23 s	12.95 s

The last action is to find the end frame for the “Last” field of the “Use frame range” option, because the retimed sequence is much longer than the original simulation. This time, the formula is:

Frame [f] = End point [s] * Frame rate [f/s]
12.95 s * 25 f/s = 324 f (frames can only be integers!)

As you can see it requires some basic math and a few calculations to get the desired curve, but with a table you will always be on the safe side. Here is the final table with the retimed X and original Y values:

X [s]	0.00 s	1.33 s	10.33 s	11.23 s	12.95 s
Y [s]	0.00 s	1.33 s	3.58 s	5.64 s	7.36 s

These values are finally entered to the curve editor. Please do not forget to change the curve's X axes to seconds with Alt + T. And here is the result with a linear interpolation between the keys:

To add the curve keys, please

double-click on the canvas to create a new key
enter the table's X value in the first field
enter the table's Y value in the second field
repeat the previous steps for the remaining values of the table.

Of course, the retimed curve should be tested with the “Timing example” feature, because it is an easy way to check if the calculation is correct.