I think somewhere between version 1.5.4 and 1.5.7 rotation got moved to "Display Matrix" side data, when in 1.5.4 and prior it was set as "rotate" metadata, when decoding a video with ffmpeg. However, I don't think there's a matching change done in FFmpegFrameRecorder - in 1.5.4 is was simply setting the "rotate" metadata to a desired rotation value, but now it has no effect and I don't see a way of altering the side data on the output video.

Am I missing something or is it a bug?