From 514a53344507ae048f4bed3a458e3f04a729ed50 Mon Sep 17 00:00:00 2001
From: Vanilagy <1696106+Vanilagy@users.noreply.github.com>
Date: Fri, 11 Jul 2025 10:07:45 +0200
Subject: [PATCH] Reduce MP3 detection false positives

---
 src/input-format.ts   | 8 +++++---
 src/mp3/mp3-misc.ts   | 4 ++++
 src/mp3/mp3-reader.ts | 2 +-
 3 files changed, 10 insertions(+), 4 deletions(-)

diff --git a/src/input-format.ts b/src/input-format.ts
index d9d34ca..8ed94f8 100644
--- a/src/input-format.ts
+++ b/src/input-format.ts
@@ -13,6 +13,7 @@ import { IsobmffReader } from './isobmff/isobmff-reader';
 import { EBMLId, EBMLReader } from './matroska/ebml';
 import { MatroskaDemuxer } from './matroska/matroska-demuxer';
 import { Mp3Demuxer } from './mp3/mp3-demuxer';
+import { FRAME_HEADER_SIZE } from './mp3/mp3-misc';
 import { Mp3Reader } from './mp3/mp3-reader';
 import { OggDemuxer } from './ogg/ogg-demuxer';
 import { OggReader } from './ogg/ogg-reader';
@@ -245,9 +246,10 @@ export class Mp3InputFormat extends InputFormat {
 		}
 
 		// Fine, we found one frame header, but we're still not entirely sure this is MP3. Let's check if we can find
-		// another header nearby:
+		// another header right after it:
 		mp3Reader.pos = firstHeader.startPos + firstHeader.totalSize;
-		const secondHeader = mp3Reader.readNextFrameHeader(Math.min(framesStartPos + 4096, sourceSize));
+		await mp3Reader.reader.loadRange(mp3Reader.pos, mp3Reader.pos + FRAME_HEADER_SIZE);
+		const secondHeader = mp3Reader.readNextFrameHeader(mp3Reader.pos + FRAME_HEADER_SIZE);
 		if (!secondHeader) {
 			return false;
 		}
@@ -257,7 +259,7 @@ export class Mp3InputFormat extends InputFormat {
 			return false;
 		}
 
-		// We have found two matching MP3 frames, a strong indicator that this is an MP3 file
+		// We have found two matching consecutive MP3 frames, a strong indicator that this is an MP3 file
 		return true;
 	}
 
diff --git a/src/mp3/mp3-misc.ts b/src/mp3/mp3-misc.ts
index 687b5f6..fdd9554 100644
--- a/src/mp3/mp3-misc.ts
+++ b/src/mp3/mp3-misc.ts
@@ -85,6 +85,10 @@ export const readFrameHeader = (word: number, reader: { pos: number; fileSize: n
 
 	reader.pos += 1;
 
+	if (firstByte !== 0xff) {
+		return null;
+	}
+
 	if ((secondByte & 0xe0) !== 0xe0) {
 		return null;
 	}
diff --git a/src/mp3/mp3-reader.ts b/src/mp3/mp3-reader.ts
index 11152ab..8425ba1 100644
--- a/src/mp3/mp3-reader.ts
+++ b/src/mp3/mp3-reader.ts
@@ -65,7 +65,7 @@ export class Mp3Reader {
 		assert(this.fileSize);
 		until ??= this.fileSize;
 
-		while (this.pos < until - FRAME_HEADER_SIZE) {
+		while (this.pos <= until - FRAME_HEADER_SIZE) {
 			const word = this.readU32();
 			this.pos -= 4;