displaymatrix handling

[dcnieho]

I tested lavfi-preview with a file source that happened to have the following side data attached to the video stream according to ffprobe:

    Side data:
      displaymatrix: rotation of -90.00 degrees

This was not honored in the playback. I am not aware of how ffmpeg normally handles this. But just in case this is something you instead of the lavfi-preview user should be handling, hereby i've reported it ;) Else just close this.