Document addition of venc_params and film_grain.
@item prft
Export encoder Producer Reference Time into packet side-data (see @code{AV_PKT_DATA_PRFT})
for codecs that support it.
+@item venc_params
+Export video encoding parameters through frame side data (see @code{AV_FRAME_DATA_VIDEO_ENC_PARAMS})
+for codecs that support it. At present, those are H.264 and VP9.
+@item film_grain
+Export film grain parameters through frame side data (see @code{AV_FRAME_DATA_FILM_GRAIN_PARAMS}).
+Supported at present by AV1 decoders.
@end table
@item error @var{integer} (@emph{encoding,video})