[FFmpeg-devel] [ANNOUNCE] New Commercial Product Using FFMPEG - Thanks To Developers.

[ffmpeg-devel at ballcam.com]

Michael Niedermayer <michaelni at gmx.at> wrote:

> On Mon, Nov 26, 2012 at 12:50:23AM +0100, Stefano Sabatini wrote:
> > On date Friday 2012-11-23 01:59:55 -0600, ffmpeg-devel at ballcam.com encoded:
> > [...]
> > > libavfilter was originally considered to do the unrotating,
> > > but as far as it is understood at this time, the rotate
> > > filter only works in 90 degree increments. (Currently
> > > FFMPEG-1.0 is used, and unless there is a need to use 
> > > a later commit, point-releases will be used).
> > > 
> > > If the FFMPEG team would like to include arbitrary angular
> > > rotation as part of the rotate libavfilter, please respond as 
> > > such to this message, and BallCam Technologies Inc. may
> > > pursue that as part of its contribution.
> > 
> > Check the (still flawed) vf_rotate.c filter in the archive. The
> > rotation angle may be injected through the metadata API into each
> > frame.
>
> but make sure you do not use some nearest neighbor code, its very bad
> quality and will be rejected if submited that way.
> the vf_perspective code is doing proper linear and cubic interpolation
> vf_rotate did nearest neighbor at some point IIRC, i dont know if the
> last patch still did
>
> [...]
> -- 
> Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB
>
> Into a blind darkness they enter who follow after the Ignorance,
> they as if into a greater darkness enter who devote themselves
> to the Knowledge alone. -- Isha Upanishad
Before I go any farther, the method I use is to crop out the central area  
from a rotated frame. (The rotated framegets larger, as you can imagine.) 
Each frame that is "unrotated" may be larger than the original. You can see
how Imagemagick, or Leptonica does it. I then crop out the common area.

If vf_rotate.c (or perspective) rotates the image, then squeezes it into
a bounding box the size of the original frame, that will not do.

Since I do a rotate, and crop, to get the common area, I refer to it as
"unrotating" since the goal is to generate a level
image, and it does.