H264Reader does not support async

[relufi]

webrtc/examples/examples/play-from-disk-h264/play-from-disk-h264.rs

Lines 172 to 175 in 8c92ba3

	// Open a H264 file and start reading using our H264Reader
	let file = File::open(&video_file_name)?;
	let reader = BufReader::new(file);
	let mut h264 = H264Reader::new(reader, 1_048_576);

H264Reader does not support async. For instance, in this example, the incorrect use of std::fs::File will block the asynchronous operation and prevent other tasks from running.