Add Packet::time_base/set_time_base

Allows inspecting and adjusting the packet's time_base.

src/codec/packet/packet.rs

@@ -143,6 +143,18 @@ impl Packet {
         self.0.dts = value.unwrap_or(AV_NOPTS_VALUE);
     }
 
+    #[inline]
+    #[cfg(feature = "ffmpeg_5_0")]
+    pub fn time_base(&self) -> Rational {
+        self.0.time_base.into()
+    }
+
+    #[inline]
+    #[cfg(feature = "ffmpeg_5_0")]
+    pub fn set_time_base(&mut self, value: Rational) {
+        self.0.time_base = value.into();
+    }
+
     #[inline]
     pub fn size(&self) -> usize {
         self.0.size as usize