Valgrind detected leak with packet.read

[xd009642]

So I need to go and make a reproducible example at some point but roughly speaking I had this code where valgrind was reporting every packet was leaked and I've commented out the fix at the bottom:

let mut packet = Packet::empty();
let mut audio = Audio::empty();
let mut resampled = Audio::empty();
'outer loop {
    match packet.read(&mut format_context) {
        Ok(_) => {
            decoder.send_packet(&packet).unwrap();
            decoder.receive_frame(&mut audio).unwrap();
            let audio = if let Some(resampler) = resampler_context.as_mut() {
                resampler.run(&audio, &mut resampled_audio).unwrap();
                &resampled_audio
            } else {
                &audio
            };
           /* This fixes the leak:
          unsafe { av_packet_unref(packet.as_mut_ptr()); }
          */
        },
        Err(_) => { break 'outer; }
    }
}

Now I would have expected this code to work without those changes because of the unrefs in av_read_frame, so maybe it's the reference counting throwing me for a loop?