From 21361d9bf882915b3a6517d6928bf4ffbd26f48b Mon Sep 17 00:00:00 2001
From: Matthew Hrehirchuk <me@matthew-hre.com>
Date: Sat, 4 Apr 2026 20:32:34 -0600
Subject: [PATCH 1/2] fix: handle av1 VideoDecoder errors

---
 src/lib/exporter/streamingDecoder.ts | 57 +++++++++++++++++++++++++++-
 1 file changed, 56 insertions(+), 1 deletion(-)

diff --git a/src/lib/exporter/streamingDecoder.ts b/src/lib/exporter/streamingDecoder.ts
index ccb510b..9786fe0 100644
--- a/src/lib/exporter/streamingDecoder.ts
+++ b/src/lib/exporter/streamingDecoder.ts
@@ -3,6 +3,51 @@ import type { SpeedRegion, TrimRegion } from "@/components/video-editor/types";
 
 const SOURCE_LOAD_TIMEOUT_MS = 60_000;
 
+/**
+ * Build a full WebCodecs-compatible AV1 codec string from the AV1CodecConfigurationRecord.
+ * web-demuxer may return a bare "av01" when the WASM-side parser fails to read
+ * the extradata (e.g. raw OBU sequence header from WebM instead of ISOBMFF av1C box).
+ * This function parses the record if present, otherwise returns a safe default.
+ *
+ * @see https://aomediacodec.github.io/av1-isobmff/#av1codecconfigurationbox-section
+ */
+function buildAV1CodecString(description?: BufferSource): string {
+	const fallback = "av01.0.01M.08";
+
+	if (!description) return fallback;
+
+	const bytes = new Uint8Array(
+		description instanceof ArrayBuffer ? description : description.buffer,
+	);
+
+	// AV1CodecConfigurationRecord layout (4+ bytes):
+	//   Byte 0: marker (1) | version (7)
+	//   Byte 1: seq_profile (3) | seq_level_idx_0 (5)
+	//   Byte 2: seq_tier_0 (1) | high_bitdepth (1) | twelve_bit (1) | ...
+	// The spec says version should be 1, but Chrome/Electron's MediaRecorder
+	// may write version 127 (0xFF first byte). We accept any version as long
+	// as the marker bit is set and the record is long enough.
+	if (bytes.length < 4) return fallback;
+	if (!(bytes[0] & 0x80)) return fallback; // marker bit must be 1
+
+	// Byte 1: seq_profile (3) | seq_level_idx_0 (5)
+	const profile = (bytes[1] >> 5) & 0x07;
+	const level = bytes[1] & 0x1f;
+
+	// Byte 2: seq_tier_0 (1) | high_bitdepth (1) | twelve_bit (1) | monochrome (1) | ...
+	const tier = (bytes[2] >> 7) & 0x01;
+	const highBitdepth = (bytes[2] >> 6) & 0x01;
+	const twelveBit = (bytes[2] >> 5) & 0x01;
+	let bitdepth = 8;
+	if (highBitdepth) bitdepth = twelveBit ? 12 : 10;
+
+	const tierChar = tier ? "H" : "M";
+	const levelStr = level.toString().padStart(2, "0");
+	const bitdepthStr = bitdepth.toString().padStart(2, "0");
+
+	return `av01.${profile}.${levelStr}${tierChar}.${bitdepthStr}`;
+}
+
 export interface DecodedVideoInfo {
 	width: number;
 	height: number;
@@ -183,7 +228,17 @@ export class StreamingVideoDecoder {
 		}
 
 		const decoderConfig = await this.demuxer.getDecoderConfig("video");
-		const codec = this.metadata.codec.toLowerCase();
+
+		// web-demuxer may return a bare "av01" for AV1 in WebM containers when the
+		// extradata isn't in the expected ISOBMFF format. WebCodecs requires the
+		// full parametrized form (e.g. "av01.0.05M.08").
+		if (/^av01$/i.test(decoderConfig.codec)) {
+			decoderConfig.codec = buildAV1CodecString(
+				decoderConfig.description as BufferSource | undefined,
+			);
+		}
+
+		const codec = decoderConfig.codec.toLowerCase();
 		const shouldPreferSoftwareDecode = codec.includes("av01") || codec.includes("av1");
 		const segments = this.splitBySpeed(
 			this.computeSegments(this.metadata.duration, trimRegions),

From 2712d8a41b86e25bcf1795e78379da846c8134a3 Mon Sep 17 00:00:00 2001
From: Matthew Hrehirchuk <me@matthew-hre.com>
Date: Sat, 4 Apr 2026 20:47:25 -0600
Subject: [PATCH 2/2] fix: use view-aware byte extraction for BufferSource
 inputs

---
 src/lib/exporter/streamingDecoder.ts | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/src/lib/exporter/streamingDecoder.ts b/src/lib/exporter/streamingDecoder.ts
index 9786fe0..ee67576 100644
--- a/src/lib/exporter/streamingDecoder.ts
+++ b/src/lib/exporter/streamingDecoder.ts
@@ -16,9 +16,10 @@ function buildAV1CodecString(description?: BufferSource): string {
 
 	if (!description) return fallback;
 
-	const bytes = new Uint8Array(
-		description instanceof ArrayBuffer ? description : description.buffer,
-	);
+	const bytes =
+		description instanceof ArrayBuffer
+			? new Uint8Array(description)
+			: new Uint8Array(description.buffer, description.byteOffset, description.byteLength);
 
 	// AV1CodecConfigurationRecord layout (4+ bytes):
 	//   Byte 0: marker (1) | version (7)