Transform360

Transform360 is a video filter that transforms 360 video in equirectangular projection into a cubemap projection. We also keep the previous version of the transform, Transform_V1, in the file vf_transform_v1.c

Advantages of Transform360

1. Transform360 achieves better performance in memory usage and visual quality. For many different algorithm and parameter settings in real-world applications, it also achieves better processing speed.
2. Transform360 allows people to have more control on the quality of the output video frames, and even the quality of different regions within a frame.
3. Transform360 separates the computation and transform logic from ffmpeg. Thus, people have much more flexibility to use different resources to develop the transforms, but do not need to be concerned with the details of the ffmpeg implementation/integration.

To Build And Use Transform360

Building

Transform360 is implemented in C++ and is invoked by an ffmpeg video filter. To build and use Transform360, follow these steps:

1. Checkout the source for the Transform360, openCV and ffmpeg.
2. Build .cpp and .h files in Transform360, together with openCV, as a library, where these files are dependent on openCV.
3. Add the Transform360 library file to the extra-libs of ffmpeg.
4. Copy vf_transform360.c to the libavfilter subdirectory in ffmpeg source.
5. Edit libavfilter/allfilters.c and register the filter by adding the line: REGISTER_FILTER(TRANSFORM360, transform360, vf); in the video filter registration section.
6. Edit libavfilter/Makefile and add the filter to adding the line: OBJS-$(CONFIG_TRANSFORM360_FILTER) += vf_transform360.o in the filter section.
7. Configure and build ffmpeg as usual.

More details about building Transform360 using CMake

1. Build with cmake.

2. Configuration for ffmpeg ./configure --prefix=/usr/local --enable-gpl --enable-nonfree --enable-libass --enable-libfdk-aac --enable-libfreetype --enable-libmp3lame --enable-libopus --enable-libtheora --enable-libvorbis --enable-libvpx --enable-libx264 --enable-libxvid --enable-libopencv --extra-libs='-lTransform360 -lstdc++'

Running

Check out the options for the filter by running ffmpeg -h filter=transform360.

A typical example looks something like:

ffmpeg -i input.mp4 
    -vf transform360="input_stereo_format=MONO
    :cube_edge_length=512
    :interpolation_alg=cubic
    :enable_low_pass_filter=1
    :enable_multi_threading=1
    :num_horizontal_segments=32
    :num_vertical_segments=15
    :adjust_kernel=1"
    output.mp4

To Build And Use Transform_V1

Building

Transform is implemented as an ffmpeg video filter. To build Transform, follow these steps:

1. Checkout the source for ffmpeg.
2. Copy vf_transform_v1.c to the libavfilter subdirectory in ffmpeg source.
3. Edit libavfilter/allfilters.c and register the filter by adding the line: REGISTER_FILTER(TRANSFORM_V1, transform_v1, vf); in the video filter registration section.
4. Edit libavfilter/Makefile and add the filter to adding the line: OBJS-$(CONFIG_TRANSFORM_V1_FILTER) += vf_transform_v1.o in the filter section.
5. Configure and build ffmpeg as usual.

Running

Check out the options for the filter by running ffmpeg -h filter=transform_v1.

A typical example looks something like:

ffmpeg -i input.mp4 
    -vf transform_v1="input_stereo_format=MONO
    :w_subdivisions=4
    :h_subdivisions=4
    :max_cube_edge_length=512" 
    output.mp4