After Effects melting film strip in the old projector
I would try using a displacement map. You can use a solid with turbulent noise on it and use it as your map, then animate the evolution, contrast and brightness so it displaces the film accordingly. If your burn is a separate layer, you can also use this as the matte for the solid with turbulent-noise in it with the effect "set matte".

Also, you might want to try to using a similar turbulent noise layer as a matte for the whole comp, meaning that the spreading bubbles from the noise (you can spread it out by pulling up a mask and keyframing the mask expansion) effectively get shuffled into your alpha-layer. If you then duplicate all this, move it one layer below, shift it to the right in the timeline (so the lower layer is about 10 frames later than the upper) and then drastically increase the contrast and lower the brightness, you will achieve some dark edges to the burnt parts.