[FFmpeg-devel] [PATCH v2] avfilter: add libdewobble_opencl filter

[Mapul Bhola]

August 23, 2021 10:43 PM, "Daniel Playfair Cal" <daniel.playfair.cal at gmail.com> wrote:

> On Tue, Aug 24, 2021 at 3:09 AM Paul B Mahol <onemda at gmail.com> wrote:
> 
>> library is named dewobble, thus filter should be libdewobble.
> 
> Lynne suggested "libdewobble_opencl". I can rename it to "libdewobble"
> if you prefer, but will everyone be happy with that?
> 
> Perhaps it will be easier if you explain the convention and your
> reasoning for the name. All the other filters which work with OpenCL
> hardware frames are postfixed with "_opencl". All the other filters
> which wrap external libraries are not prefixed with "lib" (with the
> exception of "libvmaf"). Why is this filter different in both senses?
> 
>> no, libdewobble video filter
> 
> OK, I will update this to match the name of the filter, whatever that is.
> 
>>> +
>>> +/**
>>> + * Camera properties, mirroring those present in libdewobble's camera object.
>>> + */
>>> +typedef struct Camera {
>>> + /**
>>> + * Camera projection model, e.g. `DEWOBBLE_PROJECTION_RECTILINEAR`
>>> + */
>>> + int model;
>>> +
>>> + /**
>>> + * Camera diagonal field of view in degrees
>>> + */
>>> + double diagonal_fov;
>>> +
>>> + /**
>>> + * Width in pixels
>>> + */
>>> + int width;
>>> +
>>> + /**
>>> + * Height in pixels
>>> + */
>>> + int height;
>>> +
>>> + /**
>>> + * Horizonal coordinate of focal point in pixels
>>> + */
>>> + double focal_point_x;
>>> +
>>> + /**
>>> + * Vertical coordinate of focal point in pixels
>>> + */
>>> + double focal_point_y;
>>> +} Camera;
>>> +
>>> +/**
>>> + * Motion stabilization algorithm, mirroring those available in libdewobble.
>>> + */
>>> +typedef enum StabilizationAlgorithm {
>>> +
>>> + /**
>>> + * Do not apply stabilization
>>> + */
>>> + STABILIZATION_ALGORITHM_ORIGINAL,
>>> +
>>> + /**
>>> + * Keep the camera orientation fixed at its orientation in the first frame
>>> + */
>>> + STABILIZATION_ALGORITHM_FIXED,
>>> +
>>> + /**
>>> + * Smooth camera orientation with a Savitsky-Golay filter
>>> + */
>>> + STABILIZATION_ALGORITHM_SMOOTH,
>>> +
>>> + /**
>>> + * Number of stabilization algorithms
>>> + */
>>> + NB_STABILIZATION_ALGORITHMS,
>>> +
>>> +} StabilizationAlgorithm;
>>> +
>> 
>> Huh? Why this and bellow similar stuff are not part of library?
> 
> Because the FFmpeg filter options work by writing values to offsets in
> memory, but this is not supported in libdewobble. So there are
> intermediate structs/enums in the filter context where options are
> written to, which are later passed to the libdewobble API in the
> appropriate way. e.g. see the use of dewobble_filter_config_create()
> and stabilization_algorithm.
> 
>> Apply ....
> 
> Ok, will fix.
> 
>> I really dislike GPL3 and use of opencv.
>> I would prefer pure C solution.
> 
> You are welcome to use the same ideas and write a native C filter with
> LGPL license if you want. But there will be alot more code to write.
> OpenCV provides sparse optical flow, RANSAC, warping with 5
> interpolation algorithms, text/shape drawing utilities, etc. And most
> of these with OpenCL acceleration or optimized multithreaded CPU
> implementations.
> 
> Use of OpenCV is an implementation detail of libdewobble. OpenCV is
> not used directly in the filter, and no OpenCV objects are passed to
> or received from libdewobble.

I agree with Mahol here. It's good to make sure all the code in FFmpeg meets a certain quality.
I thought there were OpenCV filters in ffmpeg already?

And if you are the writer of this plugin as well, you should consider relicensing it to LGPL for its usage in ffmpeg.
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