isSeekable
Checks if a stream may be seekable.
This is meant to be a hint. Streams may not allow seeking even if this function returns true. However, if this function returns false, streams are guaranteed to not be seekable and user interfaces may hide controls that allow seeking.
It is allowed to call method@Gtk.MediaStream.seek on a non-seekable stream, though it will not do anything.
Return
true if the stream may support seeking