[FFmpeg-devel] [PATCH] avformat/mp3dec: Workaround mp3 detection failure (PR #20212)

[quink <code@ffmpeg.org>]

PR #20212 opened by quink
URL: https://code.ffmpeg.org/FFmpeg/FFmpeg/pulls/20212
Patch URL: https://code.ffmpeg.org/FFmpeg/FFmpeg/pulls/20212.patch

A set of files begins with the following byte sequence.

00000000  4c 41 4d 45 33 2e 31 30  30 aa aa aa aa aa aa aa  |LAME3.100.......|
00000010  aa aa aa aa aa aa aa aa  aa aa aa aa aa aa aa aa  |................|
*

It seems they are encoded with lame, but missing header bytes at the
beginning.

Signed-off-by: Zhao Zhili <zhilizhao@tencent.com>


From e24f7b8d0fbc4295b3dfc9832d7b552086f45ff0 Mon Sep 17 00:00:00 2001
From: Zhao Zhili <zhilizhao@tencent.com>
Date: Mon, 11 Aug 2025 15:23:36 +0800
Subject: [PATCH] avformat/mp3dec: Workaround mp3 detection failure

A set of files begins with the following byte sequence.

00000000  4c 41 4d 45 33 2e 31 30  30 aa aa aa aa aa aa aa  |LAME3.100.......|
00000010  aa aa aa aa aa aa aa aa  aa aa aa aa aa aa aa aa  |................|
*

It seems they are encoded with lame, but missing header bytes at the
beginning.

Signed-off-by: Zhao Zhili <zhilizhao@tencent.com>
---
 libavformat/mp3dec.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/libavformat/mp3dec.c b/libavformat/mp3dec.c
index 31eeb68ebb..fd692a9c76 100644
--- a/libavformat/mp3dec.c
+++ b/libavformat/mp3dec.c
@@ -121,8 +121,11 @@ static int mp3_read_probe(const AVProbeData *p)
     // issues with MPEG-files!
     if   (first_frames>=7) return AVPROBE_SCORE_EXTENSION + 1;
     else if (max_frames>200 && p->buf_size < 2*max_framesizes)return AVPROBE_SCORE_EXTENSION;
-    else if (max_frames>=4 && p->buf_size < 2*max_framesizes) return AVPROBE_SCORE_EXTENSION / 2;
-    else if (ff_id3v2_match(buf0, ID3v2_DEFAULT_MAGIC) && 2*ff_id3v2_tag_len(buf0) >= p->buf_size)
+    else if (max_frames>=4 && p->buf_size < 2*max_framesizes) {
+        if (!memcmp(p->buf, "LAME3.100", sizeof("LAME3.100") - 1))
+            return AVPROBE_SCORE_EXTENSION - 2;
+        return AVPROBE_SCORE_EXTENSION / 2;
+    } else if (ff_id3v2_match(buf0, ID3v2_DEFAULT_MAGIC) && 2*ff_id3v2_tag_len(buf0) >= p->buf_size)
                            return p->buf_size < PROBE_BUF_MAX ? AVPROBE_SCORE_EXTENSION / 4 : AVPROBE_SCORE_EXTENSION - 2;
     else if (first_frames > 1 && whole_used) return 5;
     else if (max_frames>=1 && p->buf_size < 10*max_framesizes) return 1;
-- 
2.49.1

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