Hello, I'm investigating on possibility to encode per frame metadata using ffmpeg API. Naive attempts to set a dictionary on "AVFrame.metadata" with some key values failed without any warning or error during encoding, but no values are retrieved on the field during decoding. I'm using ffmpeg 4.1.3 with modern send/receive API usage. Other users on SO seemed to try similar approach without success[1][2]. I've no specific requirements on container format: any format supporting this feature plus streaming would be good. I first tried with flv, mp4 formats and ended up testing nut format noticing some trace of specific support for the feature[3]. Is there any obvious mistake I'm possibly doing? Is the feature actually supported? Regards, Francesco [1] https://stackoverflow.com/questions/51415447/ffmpeg-sidedata-or-metadata-per... [2] https://stackoverflow.com/questions/39330048/ffmpeg-per-frame-metadata-with-... [3] https://ffmpeg.org/pipermail/ffmpeg-devel/2013-March/141270.html