As far as I remember the spark's texture is either included in the effects.fxp or the particle.txd file.
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The original system by Rockstar is incomplete, therefore gunner was working on a project called ARS (alternative replay system):
https://www.youtube.com/results?search_query=nwpgunner+arsHe was having some issues with the GTAS community as Milbridge said and never released nor finished it.
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Sparks can perfectly be added to SA recordings. For testing I've 3D motion tracked a clip in C4D, then converted the resulting camera movement for AAE and added a textured emitter for the sparks. The Particle World emitter works 3-dimensional and just needs to follow a tracked path at the bike's rear or whatever else (rail, curb etc.). With proper masking it does look like the sparks were actually in the game and you do have full control over them. I probably still have that clip somewhere from the times when I was fucking around with ideas for a specific video.
Here's 2 examples that are poorly made in a 2D space using AAE only (kinda works, but it's nothing like what I just described above):
https://www.youtube.com/watch?v=WtW__LGQke4https://www.youtube.com/watch?v=MjpZ5oep0NA