Figure out how to get a single YUV frame from FFMPEG to send to libvmaf about libvmaf-rs

[ThatNerdUKnow]

The Data property on the VmafPicture struct is the frame data for the vmafpicture. The format is YUV.
Data is an array slice of three pointers. data[0] points to the beginning of the YUV frame, which contains the Y channel. data[1] points to the U channel, which resides after the Y channel, data[2] contains the V channel which in memory resides after the U channel. That is to say, that if we were to copy a single YUV frame into the data pointed to by data[0], data[1] and data[2] should each point to the correct memory locations for their respective channels