[FFmpeg-devel] [PATCH] avformat/amr: add P bits check to avoid mis-detects (PR #21176)

[FFmpeg-devel] [PATCH] avformat/amr: add P bits check to avoid mis-detects (PR #21176)

[Jack Lau via ffmpeg-devel]

PR #21176 opened by Jack Lau (JackLau)
URL: https://code.ffmpeg.org/FFmpeg/FFmpeg/pulls/21176
Patch URL: https://code.ffmpeg.org/FFmpeg/FFmpeg/pulls/21176.patch

Fix #21056

Refer to RFC 3267 Section 4.4.2:

A ToC entry takes the following format in octet-aligned mode:

 0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+
|F|  FT   |Q|P|P|
+-+-+-+-+-+-+-+-+

P bits: padding bits, MUST be set to zero.

Signed-off-by: Jack Lau <jacklau1222gm@gmail.com>


>From 95a39927b24e649019fdaf640dc7dd45ea1161e9 Mon Sep 17 00:00:00 2001
From: Jack Lau <jacklau1222gm@gmail.com>
Date: Fri, 12 Dec 2025 14:52:58 +0800
Subject: [PATCH] avformat/amr: add P bits check to avoid mis-detects

Fix #21056

Refer to RFC 3267 Section 4.4.2:

A ToC entry takes the following format in octet-aligned mode:

 0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+
|F|  FT   |Q|P|P|
+-+-+-+-+-+-+-+-+

P bits: padding bits, MUST be set to zero.

Signed-off-by: Jack Lau <jacklau1222gm@gmail.com>
---
 libavformat/amr.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/libavformat/amr.c b/libavformat/amr.c
index 0db0a8d26a..9cc61baf55 100644
--- a/libavformat/amr.c
+++ b/libavformat/amr.c
@@ -144,7 +144,7 @@ static int amrnb_probe(const AVProbeData *p)
 
     while (i < p->buf_size) {
         mode = b[i] >> 3 & 0x0F;
-        if (mode < 9 && (b[i] & 0x4) == 0x4) {
+        if (mode < 9 && (b[i] & 0x4) == 0x4 && (b[i] & 0x03) == 0) {
             int last = b[i];
             int size = amrnb_packed_size[mode];
             while (size--) {
@@ -201,7 +201,7 @@ static int amrwb_probe(const AVProbeData *p)
 
     while (i < p->buf_size) {
         mode = b[i] >> 3 & 0x0F;
-        if (mode < 10 && (b[i] & 0x4) == 0x4) {
+        if (mode < 10 && (b[i] & 0x4) == 0x4 && (b[i] & 0x03) == 0) {
             int last = b[i];
             int size = amrwb_packed_size[mode];
             while (size--) {
-- 
2.49.1

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