fuchsia / fuchsia / refs/heads/sandbox/ravoorir/DEBUG_FINAL_REFS / . / sdk / fidl / fuchsia.media / timeline_function.fidl

// Copyright 2018 The Fuchsia Authors. All rights reserved. | |

// Use of this source code is governed by a BSD-style license that can be | |

// found in the LICENSE file. | |

library fuchsia.media; | |

// A TimelineFunction represents a relationship between a subject timeline and a | |

// reference timeline with a linear relation. | |

// | |

// For example, consider a common use case in which reference time is the | |

// monotonic clock of a system and subject time is intended presentation time | |

// for some media such as a video. | |

// | |

// |reference_time| is the value of the monotonic clock at the beginning of | |

// playback. |subject_time| is 0 assuming playback starts at the beginning of | |

// the media. We then choose a |reference_delta| and |subject_delta| so that | |

// |subject_delta| / |reference_delta| represents the desired playback rate, | |

// e.g. 0/1 for paused and 1/1 for normal playback. | |

// | |

// ## Formulas | |

// | |

// With a function we can determine the subject timeline value |s| in terms of | |

// reference timeline value |r| with this formula (where |reference_delta| > 0): | |

// | |

// s = (r - reference_time) * (subject_delta / reference_delta) + subject_time | |

// | |

// And similarly we can find the reference timeline value |r| in terms of | |

// subject timeline value |s| with this formula (where |subject_delta| > 0): | |

// | |

// r = (s - subject_time) * (reference_delta / subject_delta) + referenc_time | |

// | |

// ## Choosing time values | |

// | |

// Time values can be arbitrary and our linear relation will of course be the | |

// same, but we can use them to represent the bounds of pieces in a piecewise | |

// linear relation. | |

// | |

// For example, if a user performs skip-chapter, we might want to describe | |

// this with a TimelineFunction whose |subject_time| is the time to skip to, | |

// |reference_time| is now plus some epsilon, and delta ratio is 1/1 for normal | |

// playback rate. | |

struct TimelineFunction { | |

// A value from the subject timeline that correlates to reference_time. | |

int64 subject_time = 0; | |

// A value from the reference timeline that correlates to subject_time. | |

int64 reference_time = 0; | |

// The change in the subject timeline corresponding to reference_delta. | |

uint32 subject_delta = 0; | |

// The change in the reference timeline corresponding to subject_delta. | |

// Cannot be zero. | |

uint32 reference_delta = 1; | |

}; |