Re: [FFmpeg-devel] [FEATURE PROPOSAL] Extracting codec-level data to binary files

From: "Ronald S. Bultje" <rsbultje@gmail.com>
To: FFmpeg development discussions and patches <ffmpeg-devel@ffmpeg.org>
Subject: Re: [FFmpeg-devel] [FEATURE PROPOSAL] Extracting codec-level data to binary files
Date: Thu, 22 May 2025 16:27:57 -0400
Message-ID: <CAEEMt2mZj17-pmOQtk0ETZLCfGQRfR72mT2O783tKkZwDKAsKA@mail.gmail.com> (raw)
In-Reply-To: <CALweWgC0jStWZCXEXARHf_fpyUzfHDc9TBk059hgLV7cAHiCuw@mail.gmail.com>

Hi,

On Thu, May 22, 2025 at 8:33 AM Ramiro Polla <ramiro.polla@gmail.com> wrote:

> On Thu, May 22, 2025 at 1:59 PM Ronald S. Bultje <rsbultje@gmail.com>
> wrote:
> > On Wed, May 21, 2025 at 9:34 AM Timothée <
> > timothee.informatique@regaud-chapuy.fr> wrote:
> > > I am interested in expanding ffmpeg's capabilities to extract
> > > low-level data from video codecs. Specifically, I'd like to implement
> > > functionality that would allow exporting frame data, macroblock
> > > information, quantization tables, and similar codec-specific elements
> > > to binary files for further analysis.
> > >
> > > After searching through the documentation and existing features, I
> > > haven't found similar functionality, though I may have missed
> > > something. Has this been implemented before, or are there related
> > > features I should examine?
> >
> > Some older codecs implement minor variants for this, e.g. grep
> > for AV_FRAME_DATA_MOTION_VECTORS, which attaches a frame's motion vectors
> > to the picture data. I believe there's an example app and possibly a
> filter
> > to overlay MVs on top of the video frame based on this concept. You could
> > extend this to cover other (macro)block info. There used to be a variant
> of
> > this for quant-tables also but I can't find it, maybe it was removed.
>
> If I recall correctly, we wanted to move away from exporting more of
> this kind of codec-specific information as picture data.
>
> Timothée, this kind of feature depends a lot on the codec that you
> want to work with. It will also depend on which syntax elements you
> need from the codec. In FFmpeg, there is the CBS code which describes
> the bitstream for a few codecs, which might help you.

I believe CBS only describes headers, not block data?

Ronald
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