av/filter/vfps.go

/*
DESCRIPTION
  A motion filter that has a variable frame rate. When motion is detected,
  the filter sends all frames and when it is not, the filter sends frames
  at a reduced rate, as set by a parameter.

AUTHORS
  Scott Barnard <scott@ausocean.org>

LICENSE
  vfps.go is Copyright (C) 2019 the Australian Ocean Lab (AusOcean)

  It is free software: you can redistribute it and/or modify them
  under the terms of the GNU General Public License as published by the
  Free Software Foundation, either version 3 of the License, or (at your
  option) any later version.

  It is distributed in the hope that it will be useful, but WITHOUT
  ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
  for more details.

  You should have received a copy of the GNU General Public License
  in gpl.txt.  If not, see http://www.gnu.org/licenses.
*/

package filter

import (
	"io"
)

// VariableFPS is a filter that has a variable frame rate. When motion is
// detected, the filter sends all frames and when it is not, the filter
// sends frames at a reduced framerate.
type VariableFPS struct {
	filter Filter
	dst    io.WriteCloser
	frames uint
	count  uint
}

// NewVariableFPS returns a pointer to a new VariableFPSFilter struct.
func NewVariableFPS(dst io.WriteCloser, minFPS float64, filter Filter) *VariableFPS {
	frames := uint(25 / minFPS)
	return &VariableFPS{filter, dst, frames, 0}
}

// Implements io.Writer.
// Write applies the motion filter to the video stream. Frames are sent
// at a reduced frame rate, except when motion is detected, then all frames
// with motion are sent.
func (v *VariableFPS) Write(f []byte) (int, error) {
	v.count = (v.count + 1) % v.frames

	if v.count == 0 {
		return v.dst.Write(f)
	}

	return v.filter.Write(f)
}

// Implements io.Closer.
// Close calls the motion filter's Close method.
func (v *VariableFPS) Close() error {
	return v.filter.Close()
}