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

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