VideoCompress.getByteThumbnail extract the same frame at different position

[stephane-archer]

final uint8list = await VideoCompress.getByteThumbnail(
  videopath,
  position: 0
);
final uint8list = await VideoCompress.getByteThumbnail(
  videopath,
  position: 10
);
final uint8list = await VideoCompress.getByteThumbnail(
  videopath,
  position: 100
);
final uint8list = await VideoCompress.getByteThumbnail(
  videopath,
  position: 1000
);

except position: 0 VideoCompress.getByteThumbnail returns the same frame each time on MacOS
it's not clear how VideoCompress.getByteThumbnail selects the frame to extract, does it use keyframe? the extracted keyframe doesn't match the position on macOS