From 9d477dfb14d5351077b8b1a3ff2a9c90263facb9 Mon Sep 17 00:00:00 2001
From: Vanilagy <1696106+Vanilagy@users.noreply.github.com>
Date: Tue, 11 Nov 2025 17:06:10 +0100
Subject: [PATCH] Allow muxing of avc3 into ISOBMFF (see #216)

---
 src/isobmff/isobmff-boxes.ts | 16 +++++++++-------
 1 file changed, 9 insertions(+), 7 deletions(-)

diff --git a/src/isobmff/isobmff-boxes.ts b/src/isobmff/isobmff-boxes.ts
index 96900d0..d7a5a38 100644
--- a/src/isobmff/isobmff-boxes.ts
+++ b/src/isobmff/isobmff-boxes.ts
@@ -577,7 +577,7 @@ export const stsd = (trackData: IsobmffTrackData) => {
 
 	if (trackData.type === 'video') {
 		sampleDescription = videoSampleDescription(
-			VIDEO_CODEC_TO_BOX_NAME[trackData.track.source._codec],
+			videoCodecToBoxName(trackData.track.source._codec, trackData.info.decoderConfig.codec),
 			trackData,
 		);
 	} else if (trackData.type === 'audio') {
@@ -1572,12 +1572,14 @@ const dataStringBoxLong = (value: string) => {
 	]);
 };
 
-const VIDEO_CODEC_TO_BOX_NAME: Record<VideoCodec, string> = {
-	avc: 'avc1',
-	hevc: 'hvc1',
-	vp8: 'vp08',
-	vp9: 'vp09',
-	av1: 'av01',
+const videoCodecToBoxName = (codec: VideoCodec, fullCodecString: string) => {
+	switch (codec) {
+		case 'avc': return fullCodecString.startsWith('avc3') ? 'avc3' : 'avc1';
+		case 'hevc': return 'hvc1';
+		case 'vp8': return 'vp08';
+		case 'vp9': return 'vp09';
+		case 'av1': return 'av01';
+	}
 };
 
 const VIDEO_CODEC_TO_CONFIGURATION_BOX: Record<VideoCodec, (trackData: IsobmffVideoTrackData) => Box | null> = {