setting the correct colormatrix in x264

[codemaster]

I have some questions about the "colormatrix" parameter from x264:

- is it mandatory to use this parameter ? If I don't use it, what are the consequences ?
- should I always use "--colormatrix bt709" for HD source, and "--colormatrix bt601" for SD ? Or something else, perhaps based on the source specifications ?

[poisondeathray]

The x264 colormatrix flags don't do anything to the actual video, it's just metadata VUI information that some players might read (the majority don't). It tells the software or hardware player what matrix to use when converting to RGB for display

It's not mandatory, but it doesn't hurt to flag it, so you should always use it (there is no downside to flagging it): usually bt709 for HD, bt601 for SD