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libvmaf

Prerequisites

For building, you need the following:

  • Python3 (3.6 or higher)
  • Meson (0.56.1 or higher)
  • Ninja (1.7.1 or higher)
  • NASM (for x86 builds only, 2.13.02 or higher)
  • xxd

Follow the steps below to set up a clean virtual environment and install the tools:

python3 -m pip install virtualenv
python3 -m virtualenv .venv
source .venv/bin/activate
pip install meson
sudo [package-manager] install nasm ninja-build doxygen xxd

You need to invoke [package-manager] depending on which system you are on: apt-get for Ubuntu and Debian, yum for CentOS and RHEL, dnf for Fedora, zypper for openSUSE, brew for MacOS (no sudo).

Ninja package name might be ninja or ninja-build, depending on your system. Check the pre-built ninja packages before running the install command.

Compile

Run:

meson build --buildtype release

(add -Denable_float=true flag in the rare case if you want to use the floating-point feature extractors.)

Build with:

ninja -vC build

Test

Build and run tests with:

ninja -vC build test

Install

Install the library, headers, and the vmaf command line tool:

ninja -vC build install

This will install the following files:

├── bin
│   └── vmaf
├── include
│   └── libvmaf
│       ├── compute_vmaf.h
│       ├── feature.h
│       ├── libvmaf.h
│       ├── model.h
│       ├── picture.h
│       └── version.h
└── lib
    ├── libvmaf.1.dylib
    ├── libvmaf.a
    ├── libvmaf.dylib -> libvmaf.1.dylib
    └── pkgconfig
        └── libvmaf.pc

Documentation

Generate HTML documentation with:

ninja -vC build doc/html

VMAF Models

libvmaf now has a number of VMAF models built-in. This means that no external VMAF model files are required, since the models are compiled into and read directly from the library. If you do not wish to compile the built-in models into your build, you may disable them with -Dbuilt_in_models=false. Previous versions of this library required a .pkl model file. Since libvmaf v2.0.0, these .pkl model files have been deprecated in favor of .json model files. If you have a previously trained .pkl model you would like to convert to .json, this Python conversion script is available.

vmaf

A command line tool called vmaf is included as part of the build/installation. See the vmaf README.md for details. An older command line tool (vmafossexec) is still part of the build but is not part of the installation. vmafossexec will be removed in a future version of this library.

API Walkthrough

Create a VmafContext with vmaf_init(). VmafContext is an opaque type, and VmafConfiguration is a options struct used to initialize the context. Be sure to clean up the VmafContext with vmaf_close() when you are done with it.

int vmaf_init(VmafContext **vmaf, VmafConfiguration cfg);

int vmaf_close(VmafContext *vmaf);

Calculating a VMAF score requires a VMAF model. The next step is to create a VmafModel. There are a few ways to get a VmafModel. Use vmaf_model_load() when you would like to load one of the default built-in models. Use vmaf_model_load_from_path() when you would like to read a model file from a filesystem. After you are done using the VmafModel, clean it up with vmaf_model_destroy().

int vmaf_model_load(VmafModel **model, VmafModelConfig *cfg,
                     const char *version);

int vmaf_model_load_from_path(VmafModel **model, VmafModelConfig *cfg,
                              const char *path);

void vmaf_model_destroy(VmafModel *model);

A VMAF score is a fusion of several elementary features which are specified by a model file. The next step is to register all feature extractors required by your model or models with vmaf_use_features_from_model(). If there are auxillary metrics (i.e. PSNR) you would also like to extract use vmaf_use_feature() to register it directly.

int vmaf_use_features_from_model(VmafContext *vmaf, VmafModel *model);

int vmaf_use_feature(VmafContext *vmaf, const char *feature_name,
                      VmafFeatureDictionary *opts_dict);

VMAF is a full-reference metric, meaning it is calculated on pairs of reference/distorted pictures. To allocate a VmafPicture use vmaf_picture_alloc. After allocation, you may fill the buffers with pixel data.

int vmaf_picture_alloc(VmafPicture *pic, enum VmafPixelFormat pix_fmt,
                        unsigned bpc, unsigned w, unsigned h);

Read all of you input pictures in a loop with vmaf_read_pictures(). When you are done reading pictures, some feature extractors may have internal buffers may still need to be flushed. Call vmaf_read_pictures() again with ref and dist set to NULL to flush these buffers. Once buffers are flushed, all further calls to vmaf_read_pictures() are invalid.

int vmaf_read_pictures(VmafContext *vmaf, VmafPicture *ref, VmafPicture *dist,
                       unsigned index);

After your pictures have been read, you can retrieve a vmaf score. Use vmaf_score_at_index to get the score at single index, and use vmaf_score_pooled() to get a pooled score across multiple frames.

int vmaf_score_at_index(VmafContext *vmaf, VmafModel *model, double *score,
                        unsigned index);

int vmaf_score_pooled(VmafContext *vmaf, VmafModel *model,
                      enum VmafPoolingMethod pool_method, double *score,
                      unsigned index_low, unsigned index_high);

For complete API documentation, see libvmaf.h. For an example of using the API to create the vmaf command line tool, see vmaf.c.

Contributing a new VmafFeatureExtractor

To write a new feature extractor, please first familiarize yourself with the VmafFeatureExtractor API documentation.

Create a new VmafFeatureExtractor and add it to the build as well as the feature_extractor_list[]. See this diff for an example. Once you do this your feature extractor may be registered and used inside of libvmaf via vmaf_use_feature() or vmaf_use_features_from_model(). To invoke this feature extractor directly from the command line with vmaf use the --feature flag.

VmafFeatureExtractor is a feature extraction class with just a few callbacks. If you have preallocations and/or precomputations to make, it is best to do this in the .init() callback and store the output in .priv. This is a place for custom data which is available for all subsequent callbacks. If you allocate anything in .init() be sure to clean it up in the .close() callback.

The remainder of your work should take place in the .extract() callback. This callback is called for every pair of input pictures. Read the pixel data make some computations and then write the output(s) to the VmafFeatureCollector via the vmaf_feature_collector_append() api. An important thing to know about this callback is that it can (and probably is) being called in an arbitrary order. If your feature extractor has a temporal requirement (i.e. motion), set the VMAF_FEATURE_EXTRACTOR_TEMPORAL flag and the VmafFeatureExtractorContext will ensure that this callback is executed in serial. For an example of a feature extractor with a temporal dependency see the motion feature extractor.

If the VMAF_FEATURE_EXTRACTOR_TEMPORAL is set, it is likely that you have buffers that need flushing. If this is the case, .flush() is called in a loop until something non-zero is returned.