support metadata output in avectroscope filter

[dave rice]

Summary of the enhancement request:

I need to test a collection of media files with stereo tracks to identify ones that are 180 degrees out of phase (or close to it). I looked at the new avectorscope filter and although it does well to visualize the phase relationship within a stereo track it doesn't output a quantified value of the phase relationship.
I suggest an output similar to ebur128 where the phase percentage is reported per audio frame and then summarized at the end of the analysis.

[Elon Musk]

I already had something like that implemented, its called correlation meter: with values between -1 (out of phase) and 1. It just did not wrote metadata but instead showed it in same frame with avectorscope output.
So i think its best to write this as new filter (with optional video output).

[Elon Musk]

Fixed in f9905e13ea1e8f3cc3971fdfc7fc8283a9779740.