I've been experimenting with cutscenes for some time now. From looking at the code, I see that the speed the video is played depends on the audio length, at least for FLC files. Since we have no tools to create an FLC file with audio support (all the modern day tools only convert to video-only), videos are played at the same rate which is 1 frame per millisecond, regardless of the headers specified in the file.
Also, i've found out that the implementarion of the FLC player does not fully comply to the standard FLIC specification. For example, TFTD defines its audio chunks in a very different way than it should, it uses 0xAAAA to define an audio chunk and adds 10 bytes after it, while the specification dictates that it should be 0x0038.
https://www.ffmpeg.org/doxygen/0.6/flic_8c-source.htmlhttps://github.com/SupSuper/OpenXcom/blob/master/src/Engine/FlcPlayer.cpphttps://www.compuphase.com/flic.htmI downloaded an old FLC compiler called EGI that could produce FLC with audio, but the game still does not recognize it because of the custom audio chunk header.
What this means, I guess, is that there will be no way to add a cutscene with audio and a proper playback rate unless the devs tweak a lot with the player code, and it still would be really hard due to the difficulty of finding a compiler that can generate FLC files with audio. I had to install EGI on a Windows XP virtual machine because it is incompatible with modern operating systems.
It would be much easier for both the devs and modders to support mpeg or other format, and leave the FLC player as is for compatibility.