[FFmpeg-devel] filtering based on exif information

Clément Bœsch u at pkh.me
Tue Nov 19 13:12:26 CET 2013

On Tue, Nov 19, 2013 at 12:35:17PM +0100, Jan Pohanka wrote:
> Dear all,

> I'm posting this in devel forum because I think that my issue will need
> some development, if not and everything can be done with current ffmpeg,
> please excuce me.

If *you* are willing to help with development that is the correct
mailing-list indeed.

> I would like to ask whether there is a possibility to filter videos with
> ffmpeg based on exif information. Please let me explain the request on
> following example:
> I have a security camera that outputs a videostream in MJPEG format. Each
> of single jpegs contains exif metadata with information about orientation
> and also information which region triggered the motion in picture detector.
> Now I need to create new video based on the original one where orientation
> of the frames will be corrected and region of MIP highlighted.
> I have checked libavfilter library and there already exists filters that
> can rotate or draw a rectangle into the frame. However I cannot imagine how
> to get also metadata there. Can someone please point me into right
> direction? I will implement it by myself, but the starting point would be
> nice... :)

We export some rotation metadata (the MOV demuxer does it), but we don't
yet honor them in the rotate/transpose filter. IIRC the current blocking
thing is because it's not transmitting the format/streams metadata to the
filters; it should probably done at init time in those filters.

Patch really welcome, I definitely want to -vf rotate=auto. Note that when
this happens, you need to drop the metadata as well so it's not rotated
twice in the output. This will need some little thinking.

Clément B.
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