feat(format/stream): expose frame-rate guessing

src/format/stream/stream.rs

@@ -1,3 +1,5 @@
+use std::ptr;
+
 use libc::c_int;
 
 use super::Disposition;
@@ -96,6 +98,23 @@ impl<'a> Stream<'a> {
 		unsafe { Rational::from((*self.as_ptr()).avg_frame_rate) }
 	}
 
+	pub fn guess_frame_rate(&self) -> Option<Rational> {
+		unsafe {
+			let r = Rational::from(av_guess_frame_rate(
+				self.context.as_ptr() as *mut _,
+				self.as_ptr() as *mut _,
+				ptr::null_mut(),
+			));
+
+			if r == Rational(0, 1) {
+				None
+			}
+			else {
+				Some(r)
+			}
+		}
+	}
+
 	pub fn metadata(&self) -> DictionaryRef<'_> {
 		unsafe { DictionaryRef::wrap((*self.as_ptr()).metadata) }
 	}