keyframes.md

Keyframe File

In order to use keyframe mode, you must have a separate file describing your keyframes. Create a text file in the same directory you are running WackyWebM. Fill the file in as detailed below.

Keyframes also require the -k argument in the command line. The complete command (with no other arguments) would look like this:

node wackywebm.js -k <keyframefile.txt> keyframes <input_file>

Keyframe File Format

Every line describes a keyframe, and consists of 4 values. The last value is optional and can be left out. They are all separated by comma characters (,)

• First, the time in the video of the keyframe. This is either of these two options:
  • One integer representing seconds in the video
  • Two integers, separated by any one of the characters ., : or -, where the first still represents seconds, and the second represents frames (so for example, 1.5 does not represent 1.5 seconds, but represents the fifth frame after the first second of the video)
• Next, the width of the video, followed by its height - both of these support some very basic mathematical expressions and some placeholders (for example last/2 means to scale the video to half its size at the last keyframe)
• Finally, the interpolation with which to advance towards the next keyframe - currently, the following are supported:
  • linear: linearly interpolates towards the next keyframe.
  • instant: instantly jumps to the next keyframe at its time - unlike the name might imply, it does not create a jump from the last keyframe to the current one.

The interpolation mode is optional and if not given, linear is used as a default.

If it isn't overwritten, an implicit keyframe at 0 frames into the video is added with linear interpolation and the video's original size.

To use this mode, add -k with the path to your file (do not supply the keyframe data itself to the -k flag).

Also, any lines that are entirely whitespace or start in a # character are ignored.

Example

# for easier explanations, lets assume the original video is 1000x1000 pixels.

# 0.1 means 0 seconds and 1 frame. this "jumps" the video size to 300x300 at the very first frame, 
# and then slowly interpolates towards the next frame (because "linear" is implied)
0.1, 300, 300

# after 1.5 seconds, the video would be approximately 450 pixels in width and 225 in height,
# since the scaling is linear and that time is about halfway between the two keyframes, so
# it's expected that the size is roughly halfway between 300x300 and 600x150
3, last*2, last/2

# slowly scale the video up to 1000x1000 (the original resolution) over 7 seconds, then keep it there until the next keyframe
# (in this case, for 5 seconds) where it "jumps" to 100x100
10, original, original, instant

15, 100, 100
# since there are no further keyframes after this one, the video stays at the size of
# 100x100 pixels from 15 seconds until the end.