Rewrite timestamps on clusters to allow splicing

src/bin/resynth.rs

@@ -45,6 +45,10 @@ pub fn main() {
         encode_webm_element(&fixer.process(element), &mut cursor).unwrap();
     }
 
+    for element in &body {
+        encode_webm_element(&fixer.process(element), &mut cursor).unwrap();
+    }
+
     output = cursor.into_inner();
     stdout().write_all(&output).unwrap();
     output.clear();

src/timecode_fixer.rs

@@ -2,16 +2,41 @@
 use webm::WebmElement;
 
 pub struct TimecodeFixer {
+    pub current_offset: u64,
+    pub last_cluster_base: u64,
+    pub last_observed_timecode: u64,
+    pub assumed_duration: u64
 }
 
 impl TimecodeFixer {
     pub fn new() -> TimecodeFixer {
         TimecodeFixer {
+            current_offset: 0,
+            last_cluster_base: 0,
+            last_observed_timecode: 0,
+            assumed_duration: 33
         }
     }
 
     pub fn process<'b>(&mut self, element: &WebmElement<'b>) -> WebmElement<'b> {
         match element {
+            &WebmElement::Timecode(timecode) => {
+                // detect a jump backwards in the source, meaning we need to recalculate our offset
+                if timecode < self.last_cluster_base {
+                    let next_timecode = self.last_observed_timecode + self.assumed_duration;
+                    self.current_offset = next_timecode - timecode;
+                }
+
+                // remember the source timecode to detect future jumps
+                self.last_cluster_base = timecode;
+
+                // return adjusted timecode
+                WebmElement::Timecode(timecode + self.current_offset)
+            },
+            &WebmElement::SimpleBlock(block) => {
+                self.last_observed_timecode = self.last_cluster_base + (block.timecode as u64);
+                *element
+            },
             _ => *element
         }
     }