fix(moq-hls): account for audio groups in master variants (moq-dev#2264)

Co-authored-by: Codex <codex@openai.com>

Author: kixelated

rs/moq-hls/src/export/master.rs

@@ -3,6 +3,7 @@
 //! URIs are relative to the master playlist (`/<broadcast>/master.m3u8`), so a
 //! rendition's `<name>/media.m3u8` resolves under the broadcast directory.
 
+use std::collections::BTreeMap;
 use std::fmt::Write;
 
 const VERSION: u32 = 9;
@@ -32,41 +33,86 @@ pub struct AudioVariant {
 	pub codec: String,
 }
 
-/// Render the multivariant playlist. The first audio rendition is marked default.
+struct AudioGroup<'a> {
+	id: String,
+	bandwidth: u64,
+	codec: &'a str,
+	variants: Vec<&'a AudioVariant>,
+}
+
+fn group_audio(audio: &[AudioVariant]) -> Vec<AudioGroup<'_>> {
+	let mut codecs = BTreeMap::<&str, Vec<&AudioVariant>>::new();
+	for variant in audio {
+		codecs.entry(&variant.codec).or_default().push(variant);
+	}
+
+	let multiple = codecs.len() > 1;
+	codecs
+		.into_iter()
+		.enumerate()
+		.map(|(index, (codec, variants))| AudioGroup {
+			id: if multiple {
+				format!("{AUDIO_GROUP}-{index}")
+			} else {
+				AUDIO_GROUP.to_string()
+			},
+			bandwidth: variants
+				.iter()
+				.map(|variant| variant.bandwidth)
+				.max()
+				.unwrap_or_default(),
+			codec,
+			variants,
+		})
+		.collect()
+}
+
+fn render_video(out: &mut String, variant: &VideoVariant, audio: Option<&AudioGroup<'_>>) {
+	let bandwidth = variant
+		.bandwidth
+		.saturating_add(audio.map_or(0, |group| group.bandwidth));
+	let codecs = audio.map_or_else(
+		|| variant.codec.clone(),
+		|group| format!("{},{}", variant.codec, group.codec),
+	);
+	let mut line = format!("#EXT-X-STREAM-INF:BANDWIDTH={bandwidth}");
+	if let (Some(w), Some(h)) = (variant.width, variant.height) {
+		let _ = write!(line, ",RESOLUTION={w}x{h}");
+	}
+	let _ = write!(line, ",CODECS=\"{codecs}\"");
+	if let Some(group) = audio {
+		let _ = write!(line, ",AUDIO=\"{}\"", group.id);
+	}
+	let _ = writeln!(out, "{line}");
+	let _ = writeln!(out, "{}/media.m3u8", variant.name);
+}
+
+/// Render the multivariant playlist. The first rendition in each audio codec group is default.
 pub fn render_master(video: &[VideoVariant], audio: &[AudioVariant]) -> String {
 	let mut out = String::new();
 	let _ = writeln!(out, "#EXTM3U");
 	let _ = writeln!(out, "#EXT-X-VERSION:{VERSION}");
 
-	let has_audio = !audio.is_empty();
-	for (index, variant) in audio.iter().enumerate() {
-		let default = if index == 0 { "YES" } else { "NO" };
-		let _ = writeln!(
-			out,
-			"#EXT-X-MEDIA:TYPE=AUDIO,GROUP-ID=\"{AUDIO_GROUP}\",NAME=\"{}\",DEFAULT={default},AUTOSELECT=YES,URI=\"{}/media.m3u8\"",
-			variant.name, variant.name
-		);
+	let audio_groups = group_audio(audio);
+	for group in &audio_groups {
+		for (index, variant) in group.variants.iter().enumerate() {
+			let default = if index == 0 { "YES" } else { "NO" };
+			let _ = writeln!(
+				out,
+				"#EXT-X-MEDIA:TYPE=AUDIO,GROUP-ID=\"{}\",NAME=\"{}\",DEFAULT={default},AUTOSELECT=YES,URI=\"{}/media.m3u8\"",
+				group.id, variant.name, variant.name
+			);
+		}
 	}
 
-	// One audio codec is enough for the combined CODECS attribute.
-	let audio_codec = audio.first().map(|a| a.codec.as_str());
-
 	for variant in video {
-		let codecs = match audio_codec {
-			Some(audio) => format!("{},{}", variant.codec, audio),
-			None => variant.codec.clone(),
-		};
-
-		let mut line = format!("#EXT-X-STREAM-INF:BANDWIDTH={}", variant.bandwidth);
-		if let (Some(w), Some(h)) = (variant.width, variant.height) {
-			let _ = write!(line, ",RESOLUTION={w}x{h}");
+		if audio_groups.is_empty() {
+			render_video(&mut out, variant, None);
+		} else {
+			for group in &audio_groups {
+				render_video(&mut out, variant, Some(group));
+			}
 		}
-		let _ = write!(line, ",CODECS=\"{codecs}\"");
-		if has_audio {
-			let _ = write!(line, ",AUDIO=\"{AUDIO_GROUP}\"");
-		}
-		let _ = writeln!(out, "{line}");
-		let _ = writeln!(out, "{}/media.m3u8", variant.name);
 	}
 
 	// Audio-only broadcast: still expose a playable variant per audio rendition.
@@ -109,11 +155,57 @@ mod tests {
 			"#EXT-X-MEDIA:TYPE=AUDIO,GROUP-ID=\"aud\",NAME=\"audio\",DEFAULT=YES,AUTOSELECT=YES,URI=\"audio/media.m3u8\"\n"
 		));
 		assert!(out.contains(
-			"#EXT-X-STREAM-INF:BANDWIDTH=2500000,RESOLUTION=1280x720,CODECS=\"avc1.42c01f,mp4a.40.2\",AUDIO=\"aud\"\n"
+			"#EXT-X-STREAM-INF:BANDWIDTH=2628000,RESOLUTION=1280x720,CODECS=\"avc1.42c01f,mp4a.40.2\",AUDIO=\"aud\"\n"
 		));
 		assert!(out.contains("\nvideo/media.m3u8\n"));
 	}
 
+	#[test]
+	fn separates_audio_codecs_into_accurate_variants() {
+		let video = vec![VideoVariant {
+			name: "video".into(),
+			bandwidth: 2_500_000,
+			width: Some(1280),
+			height: Some(720),
+			codec: "avc1.42c01f".into(),
+		}];
+		let audio = vec![
+			AudioVariant {
+				name: "aac-low".into(),
+				bandwidth: 96_000,
+				codec: "mp4a.40.2".into(),
+			},
+			AudioVariant {
+				name: "aac-high".into(),
+				bandwidth: 128_000,
+				codec: "mp4a.40.2".into(),
+			},
+			AudioVariant {
+				name: "opus".into(),
+				bandwidth: 160_000,
+				codec: "opus".into(),
+			},
+		];
+
+		let out = render_master(&video, &audio);
+		assert!(out.contains(
+			"#EXT-X-MEDIA:TYPE=AUDIO,GROUP-ID=\"aud-0\",NAME=\"aac-low\",DEFAULT=YES,AUTOSELECT=YES,URI=\"aac-low/media.m3u8\"\n"
+		));
+		assert!(out.contains(
+			"#EXT-X-MEDIA:TYPE=AUDIO,GROUP-ID=\"aud-0\",NAME=\"aac-high\",DEFAULT=NO,AUTOSELECT=YES,URI=\"aac-high/media.m3u8\"\n"
+		));
+		assert!(out.contains(
+			"#EXT-X-MEDIA:TYPE=AUDIO,GROUP-ID=\"aud-1\",NAME=\"opus\",DEFAULT=YES,AUTOSELECT=YES,URI=\"opus/media.m3u8\"\n"
+		));
+		assert!(out.contains(
+			"#EXT-X-STREAM-INF:BANDWIDTH=2628000,RESOLUTION=1280x720,CODECS=\"avc1.42c01f,mp4a.40.2\",AUDIO=\"aud-0\"\n"
+		));
+		assert!(out.contains(
+			"#EXT-X-STREAM-INF:BANDWIDTH=2660000,RESOLUTION=1280x720,CODECS=\"avc1.42c01f,opus\",AUDIO=\"aud-1\"\n"
+		));
+		assert_eq!(out.matches("\nvideo/media.m3u8\n").count(), 2);
+	}
+
 	#[test]
 	fn audio_only_is_playable() {
 		let audio = vec![AudioVariant {