using System;
using System.Text.RegularExpressions;

public class Test
{
	public static void Main()
	{
		string s = "  Stream #0:0(und): Video: h264 (Constrained Baseline) (avc1 / 0x31637661), yuv420p, 480x480 [SAR 1:1 DAR 1:1], 868 kb/s, 29.97 fps, 29.97 tbr, 11988 tbn (default)";
		Match m = Regex.Match(s, @"\b([0-9]+(?:\.[0-9]+)?) fps\b");
		if (m.Success) {
		    Console.WriteLine(m.Groups[1].Value);
		}
	}
}