From: Michael Niedermayer <michael@niedermayer.cc>
To: FFmpeg development discussions and patches <ffmpeg-devel@ffmpeg.org>
Subject: Re: [FFmpeg-devel] [PATCH] avformat/mp3dec: Workaround mp3 detection failure (PR #20212)
Date: Mon, 11 Aug 2025 12:51:38 +0200
Message-ID: <20250811105138.GX29660@pb2> (raw)
In-Reply-To: <20250811083755.CDB4D68BEE9@ffbox0-bg.ffmpeg.org>
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On Mon, Aug 11, 2025 at 11:37:55AM +0300, quink wrote:
> 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)
why is this needed ?
Naively i would expect that the probe code would detect a mp3 stream like this
based on max_frames
why does that fail ?
as what is teh stream detected instead ?
maybe whatever detects it, is wrong instead and can be improved by not missdetecting it
thx
[...]
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Michael GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB
If the United States is serious about tackling the national security threats
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values corporate profits and government espionage over security.-Bruce Schneier
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next parent reply other threads:[~2025-08-11 10:51 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <20250811083755.CDB4D68BEE9@ffbox0-bg.ffmpeg.org>
2025-08-11 10:51 ` Michael Niedermayer [this message]
2025-08-11 12:04 ` Zhao Zhili
[not found] <20250811083754.1578368D1B5@ffbox0-bg.ffmpeg.org>
2025-08-11 8:40 ` Nicolas George
2025-08-11 9:46 ` Zhao Zhili
2025-08-11 9:51 ` Nicolas George
2025-08-11 10:13 ` Zhao Zhili
2025-08-11 10:17 ` Nicolas George
2025-08-11 10:49 ` Zhao Zhili
2025-08-11 10:53 ` Nicolas George
2025-08-11 8:37 quink
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