Klarity

Klarity is an FFMpeg-based media player library written in C++ and Kotlin, and supports use in Jetpack Compose Desktop projects.

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Table of Content

• Features
• Architecture
  • Dependency graph
  • State diagram
  • Transition table
• Supported formats
• Modules
  • Core
  • Compose
  • Example
• Components
• Installation

Features

• Media playback (audio, video)
• Change playback speed with time stretching (without affecting pitch)
• Continuous preview for timeline-like features
• Creation of snapshots by timestamps
• Coroutines/Flow based API
• Compose video rendering

Architecture

Dependency graph

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graph TD
    KlarityPlayer --> PlayerController
    PlayerController --> Pipeline
    PlayerController --> BufferLoop
    PlayerController --> PlaybackLoop
    PlayerController --> Settings
    PlayerController --> PlayerState
    PlayerController --> BufferTimestamp
    PlayerController --> PlaybackTimestamp
    PlayerController --> Renderer
    PlayerController --> Events
    BufferLoop --> Pipeline
    PlaybackLoop --> BufferLoop
    PlaybackLoop --> Pipeline
    PlayerController --> Pipeline
    subgraph Pipeline
        Pipeline.AudioVideo --> Media
        Pipeline.AudioVideo --> AudioDecoder
        Pipeline.AudioVideo --> VideoDecoder
        Pipeline.AudioVideo --> AudioBuffer
        Pipeline.AudioVideo --> VideoBuffer
        Pipeline.AudioVideo --> Sampler
        Pipeline.AudioVideo --> Renderer
        Pipeline.Audio --> Media
        Pipeline.Audio --> AudioDecoder
        Pipeline.Audio --> AudioBuffer
        Pipeline.Audio --> Sampler
        Pipeline.Video --> Media
        Pipeline.Video --> VideoDecoder
        Pipeline.Video --> VideoBuffer
        Pipeline.Video --> Renderer
    end
    Sampler --> JNI\nNativeSampler --> C++\nSampler
    AudioDecoder --> JNI\nNativeDecoder
    VideoDecoder --> JNI\nNativeDecoder
    JNI\nNativeDecoder --> C++\nDecoder

State diagram

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stateDiagram-v2
    state PlayerState {
        [*] --> Empty
        Empty --> Preparing: Prepare Media
        Preparing --> Ready: Media Ready
        Preparing --> Empty: Release

        state Ready {
            [*] --> Stopped
            Stopped --> Playing: Play
            Playing --> Paused: Pause
            Playing --> Stopped: Stop
            Playing --> Seeking: SeekTo
            Paused --> Playing: Resume
            Paused --> Stopped: Stop
            Paused --> Seeking: SeekTo
            Stopped --> Completed: Playback Completed
            Stopped --> Seeking: SeekTo
            Completed --> Stopped: Stop
            Completed --> Seeking: SeekTo
            Seeking --> Seeking: SeekTo
            Seeking --> Paused: Seek Completed
            Seeking --> Stopped: Stop
        }

        Ready --> Empty: Release
    }

Transition table

Current State \ Target State	Empty	Preparing	Ready (Stopped)	Ready (Playing)	Ready (Paused)	Ready (Completed)	Ready (Seeking)	Released
Empty	N/A	Prepare	N/A	N/A	N/A	N/A	N/A	N/A
Preparing	N/A	N/A	Media Ready	N/A	N/A	N/A	N/A	Release
Ready (Stopped)	N/A	N/A	N/A	Play	N/A	N/A	SeekTo	Release
Ready (Playing)	N/A	N/A	Stop	N/A	Pause	N/A	SeekTo	N/A
Ready (Paused)	N/A	N/A	Stop	Resume	N/A	N/A	SeekTo	N/A
Ready (Completed)	N/A	N/A	Stop	N/A	N/A	N/A	SeekTo	N/A
Ready (Seeking)	N/A	N/A	Stop	N/A	Seek Completed	N/A	SeekTo	N/A

Supported formats

Full list of formats supported by FFmpeg

Modules

Core

Contains basic components such as: controller, player, preview manager, snapshot manager

Dependencies

• klarity-decoder

  • FFmpeg

• klarity-sampler

  • PortAudio
  • Signalsmith Audio

Compose

Contains a Compose component for rendering video

Dependencies

• Core Module

Example

Contains a demo application

Dependencies

• Core Module
• Compose Module

To run demo application place the binaries appropriate to your platform into the example/bin folder and run the Application.

Components

• KlarityPlayer - contains the media player logic.
• SnapshotManager - allows to get frames (snapshots) with a specified timestamp once per session. Use case - previewing keyframes.
• PreviewManager - allows to get frames ( snapshots) with a specific timestamp during a continuous session. Use case - previewing the timeline.
• Renderer - Provides functionality for rendering background and foreground.

Installation and usage

Important

Binaries must be located in the filesystem, however, they can be part of a jar - for this the binaries must be opened as temporary files whose path can be used by the loader.

• Include the library jars in project
• Place binaries in folder
• Load binaries by specifying path in calls to loadDecoder and loadSampler functions of Klarity loader object
• Instantiate and use core media player components located in com.github.numq.klarity.core
• Instantiate and use specific Jetpack Compose components located in com.github.numq.klarity.compose