Re: [FFmpeg-devel] [PATCH] avformat/demux: avoid unconditional ID3v2 tag consumption - Nil Fons Miret via ffmpeg-devel

From: Nil Fons Miret via ffmpeg-devel <ffmpeg-devel@ffmpeg.org>
To: FFmpeg development discussions and patches <ffmpeg-devel@ffmpeg.org>
Cc: Nil Fons Miret <nilf@netflix.com>, Kyle Swanson <kswanson@netflix.com>
Subject: Re: [FFmpeg-devel] [PATCH] avformat/demux: avoid unconditional ID3v2 tag consumption
Date: Wed, 23 Jul 2025 13:50:33 -0400
Message-ID: <CAPf3GF=b5Y0LGE9kxbxnJ_rtii6XSNed8UoWPo6V8CZshA=aGQ@mail.gmail.com> (raw)
In-Reply-To: <CAPf3GFnAqQrr2+O8j8iMmL5VThbGwOnyu4U+ARwXP-ODdM+gKg@mail.gmail.com>

Hi,

Pinging this patch from a couple weeks ago. To be clear, I am not sure
how people typically use ffmpeg's ID3v2 support, so please let me know
if the patch is missing something and I'm happy to iterate on it, but
it does seem to me that trying to parse it from rawvideo inputs is
wrong.

Thank you,
Nil

On Tue, Jul 8, 2025 at 6:07 PM Nil Fons Miret <nilf@netflix.com> wrote:
>
> I have found a few instances of rawvideo files that coincidentally
> start with a header matching the ID3v2 header format, and ffmpeg
> consumes the header before demuxing, causing a decoding error. This
> happens even if "-f rawvideo" is specified.
>
> This patch limits the formats for which this automatic consuming of
> ID3v2 headers is done. Note: I am not an expert in ID3v2 by any means,
> and I'm happy to accept suggestions, both on the scope and mechanism
> of the solution.
>
> To reproduce, you can easily generate an example as follows:
>
> ```
> (  echo "49 44 33 2B 98 3A 49 44 33 2B 98 3A 6A 44 54 2B" | xxd -r -p
>   dd if=/dev/zero bs=1 count=115184 2>/dev/null
> ) > id3v2_320x240_yuv420p.yuv
>
>
> ffmpeg -f rawvideo -s 320x240 -pix_fmt yuv420p -i
> id3v2_320x240_yuv420p.yuv -f null -
> ```
>
> This generates a 320x240 yuv420p file with a 16-byte header that
> matches the ID3v2 header format (this was copied from a real case I
> saw) and completed with zeroes for a total of 115200 bytes, the right
> size for this resolution and pixel format.
>
> On the master branch, I see:
> ```
> [...]
> ID3v2.43 tag skipped, cannot handle version
> [...]
> [out#0/null @ 0x15700a6e0] Output file is empty, nothing was
> encoded(check -ss / -t / -frames parameters if used)
> frame=    0 fps=0.0 q=0.0 Lsize=N/A time=N/A bitrate=N/A speed=N/A
> ```
>
> After the changes: it decodes as expected.
> ```
> [...]
> frame=    1 fps=0.0 q=-0.0 Lsize=N/A time=00:00:00.04 bitrate=N/A
> speed=16.5x elapsed=0:00:00.00
> ```
>
> Thanks in advance,
> Nil
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