UI: improve aspect ratio handling

As written in the changelog: Live streams formerly worked around a
Firefox pixel aspect ratio bug by forcing all videos to 16:9, which
dramatically distorted 9:16 camera views. Playback didn't, so anamorphic
videos looked correct on Chrome but slightly stretched on Firefox. Now
both live streams and playback are fully correct on all browsers.

server/Cargo.lock

@@ -1264,6 +1264,7 @@ dependencies = [
  "moonfire-base",
  "mylog",
  "nix 0.22.0",
+ "num-rational 0.4.0",
  "odds",
  "parking_lot",
  "pretty-hex",

server/db/Cargo.toml

@@ -29,6 +29,7 @@ libpasta = "0.1.2"
 log = "0.4"
 mylog = { git = "https://github.com/scottlamb/mylog" }
 nix = "0.22.0"
+num-rational = { version = "0.4.0", default-features = false, features = ["std"] }
 odds = { version = "0.4.0", features = ["std-vec"] }
 parking_lot = { version = "0.11.1", features = [] }
 pretty-hex = "0.2.1"

server/db/db.rs

@@ -135,6 +135,16 @@ pub struct VideoSampleEntry {
     pub pasp_v_spacing: u16,
 }
 
+impl VideoSampleEntry {
+    /// Returns the aspect ratio as a minimized ratio.
+    pub fn aspect(&self) -> num_rational::Ratio<u32> {
+        num_rational::Ratio::new(
+            u32::from(self.width) * u32::from(self.pasp_h_spacing),
+            u32::from(self.height) * u32::from(self.pasp_v_spacing),
+        )
+    }
+}
+
 #[derive(PartialEq, Eq)]
 pub struct VideoSampleEntryToInsert {
     pub data: Vec<u8>,

server/src/json.rs

@@ -496,15 +496,20 @@ pub struct VideoSampleEntry {
     pub height: u16,
     pub pasp_h_spacing: u16,
     pub pasp_v_spacing: u16,
+    pub aspect_width: u32,
+    pub aspect_height: u32,
 }
 
 impl VideoSampleEntry {
     fn from(e: &db::VideoSampleEntry) -> Self {
+        let aspect = e.aspect();
         Self {
             width: e.width,
             height: e.height,
             pasp_h_spacing: e.pasp_h_spacing,
             pasp_v_spacing: e.pasp_v_spacing,
+            aspect_width: *aspect.numer(),
+            aspect_height: *aspect.denom(),
         }
     }
 }

server/src/mp4.rs

@@ -1928,6 +1928,15 @@ impl http_serve::Entity for File {
                     );
                 }
             }
+        } else if self.0.type_ == Type::InitSegment {
+            // FileBuilder::build() should have failed if there were no video_sample_entries.
+            let ent = self.0.video_sample_entries.first().expect("no video_sample_entries");
+            let aspect = ent.aspect();
+            hdrs.insert("X-Aspect",
+                HeaderValue::try_from(
+                    format!("{}:{}", aspect.numer(), aspect.denom())
+                ).expect("no invalid chars in X-Aspect format")
+            );
         }
     }
     fn last_modified(&self) -> Option<SystemTime> {
@@ -2690,6 +2699,9 @@ mod tests {
         let mp4 = builder
             .build(db.db.clone(), db.dirs_by_stream_id.clone())
             .unwrap();
+        let mut hdrs = http::header::HeaderMap::new();
+        mp4.add_headers(&mut hdrs);
+        assert_eq!(hdrs.get("X-Aspect").unwrap(), "16:9");
         traverse(mp4.clone()).await;
     }