From 2c96ec0f1b57b5bc3adae1cff99be9b4b99fe88d Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Jonas=20Lid=C3=A9n?= <jonas@lideen.se>
Date: Thu, 13 Nov 2025 09:34:29 +0100
Subject: [PATCH] feature(isobmff): read disabled tracks (#214)

* feature(isobmff): read disabled tracks

* Put enabled ISOBMFF tracks first

---------

Co-authored-by: Vanilagy <1696106+Vanilagy@users.noreply.github.com>
---
 src/isobmff/isobmff-demuxer.ts | 13 +++++++++----
 1 file changed, 9 insertions(+), 4 deletions(-)

diff --git a/src/isobmff/isobmff-demuxer.ts b/src/isobmff/isobmff-demuxer.ts
index 35e90ae..aa34771 100644
--- a/src/isobmff/isobmff-demuxer.ts
+++ b/src/isobmff/isobmff-demuxer.ts
@@ -92,6 +92,7 @@ type InternalTrack = {
 	id: number;
 	demuxer: IsobmffDemuxer;
 	inputTrack: InputTrack | null;
+	isDefault: boolean;
 	timescale: number;
 	durationInMovieTimescale: number;
 	durationInMediaTimescale: number;
@@ -315,6 +316,9 @@ export class IsobmffDemuxer extends Demuxer {
 					this.moovSlice = moovSlice;
 					this.readContiguousBoxes(this.moovSlice);
 
+					// Put default tracks first
+					this.tracks.sort((a, b) => Number(b.isDefault) - Number(a.isDefault));
+
 					for (const track of this.tracks) {
 						// Modify the edit list offset based on the previous segment durations. They are in different
 						// timescales, so we first convert to seconds and then into the track timescale.
@@ -651,6 +655,7 @@ export class IsobmffDemuxer extends Demuxer {
 					id: -1,
 					demuxer: this,
 					inputTrack: null,
+					isDefault: false,
 					info: null,
 					timescale: -1,
 					durationInMovieTimescale: -1,
@@ -695,10 +700,10 @@ export class IsobmffDemuxer extends Demuxer {
 				const version = readU8(slice);
 				const flags = readU24Be(slice);
 
-				const trackEnabled = (flags & 0x1) !== 0;
-				if (!trackEnabled) {
-					break;
-				}
+				// Spec says disabled tracks are to be treated like they don't exist, but in practice, they are treated
+				// more like non-default tracks.
+				const trackEnabled = !!(flags & 0x1);
+				track.isDefault = trackEnabled;
 
 				// Skip over creation & modification time to reach the track ID
 				if (version === 0) {