[Cin] Multitrack performance issues

[Andrea paz]

Adam wrote in his "Secrets of Cinelerra", that the compositing engine
is different and slower than the decoding/playback engine:
"Cinelerra detects when it's in a compositing operation and plays back
through the compositing engine only then. Otherwise, it uses the
fastest decoder available in the hardware."
This sentence is also stated in our manual.
Could it be that in the case of multi-tracks and effects we enter the
“compositing” mode resulting in less efficiency and speed?

Note to @Georgy
I have included your explanations on Dissolve/alpha channel in the
manual. Do you think this is okay or do you have other suggestions?
https://git.cinelerra-gg.org/git/?p=goodguy/cin-manual-latex.git;a=blob;f=parts/Faq.tex;h=8bc0b6f20d921602fabb82a6df1e8d3e73b43464;hb=2b51d361d58f64919dae318d9bdc13cb50db0264