[FFmpeg-user] Modify FFMP Vendor FourCC for ProRes Videostream

[Marcel Hinsch]

Hello,

Looking into FFMPEG's source when trying to figure out how to change a 
ProRes Video Stream's vendor tag (which is required for certain automated 
spec compliency tests), I have found that the vendor code is hard-coded to 
"FFMP" as visible on this line of code: 
https://github.com/FFmpeg/FFmpeg/blob/c75dfa043585db7f5e20f5cab2ca8be1771ca7b6/libavformat/movenc.c#L2128
. Being hardcoded, it doesn't seem like it can be changed unless the 
source is forked. Is there a reason this is set to "FFMP"? Would there be 
an issue changing it to "appl"? Why was a different value from "appl" 
chosen in the first place?

Sincerely,
Marcel