Gstreamer video snapshot

public bool take_snapshot (string destination, string mime) {
    var caps = Gst.Caps.from_string (mime);
    Gst.Sample sample;
    Signal.emit_by_name (playbin, "convert-sample", caps, out sample);
    if (sample == null)
        return false;
    var buffer = sample.get_buffer();
    if (buffer == null)
        return false;
    Gst.MapInfo info;
    buffer.get_memory (0).map (out info, Gst.MapFlags.READ);
    FileUtils.set_data (destination, info.data);
}