timefilter.h 3.8 KB

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  1. /*
  2. * Delay Locked Loop based time filter prototypes and declarations
  3. * Copyright (c) 2009 Samalyse
  4. * Copyright (c) 2009 Michael Niedermayer
  5. * Author: Olivier Guilyardi <olivier samalyse com>
  6. * Michael Niedermayer <michaelni gmx at>
  7. *
  8. * This file is part of FFmpeg.
  9. *
  10. * FFmpeg is free software; you can redistribute it and/or
  11. * modify it under the terms of the GNU Lesser General Public
  12. * License as published by the Free Software Foundation; either
  13. * version 2.1 of the License, or (at your option) any later version.
  14. *
  15. * FFmpeg is distributed in the hope that it will be useful,
  16. * but WITHOUT ANY WARRANTY; without even the implied warranty of
  17. * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
  18. * Lesser General Public License for more details.
  19. *
  20. * You should have received a copy of the GNU Lesser General Public
  21. * License along with FFmpeg; if not, write to the Free Software
  22. * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
  23. */
  24. #ifndef AVDEVICE_TIMEFILTER_H
  25. #define AVDEVICE_TIMEFILTER_H
  26. /**
  27. * Opaque type representing a time filter state
  28. *
  29. * The purpose of this filter is to provide a way to compute accurate time
  30. * stamps that can be compared to wall clock time, especially when dealing
  31. * with two clocks: the system clock and a hardware device clock, such as
  32. * a soundcard.
  33. */
  34. typedef struct TimeFilter TimeFilter;
  35. /**
  36. * Create a new Delay Locked Loop time filter
  37. *
  38. * feedback2_factor and feedback3_factor are the factors used for the
  39. * multiplications that are respectively performed in the second and third
  40. * feedback paths of the loop.
  41. *
  42. * Unless you know what you are doing, you should set these as follow:
  43. *
  44. * o = 2 * M_PI * bandwidth * period_in_seconds
  45. * feedback2_factor = sqrt(2) * o
  46. * feedback3_factor = o * o
  47. *
  48. * Where bandwidth is up to you to choose. Smaller values will filter out more
  49. * of the jitter, but also take a longer time for the loop to settle. A good
  50. * starting point is something between 0.3 and 3 Hz.
  51. *
  52. * @param time_base period of the hardware clock in seconds
  53. * (for example 1.0/44100)
  54. * @param period expected update interval, in input units
  55. * @param brandwidth filtering bandwidth, in Hz
  56. *
  57. * @return a pointer to a TimeFilter struct, or NULL on error
  58. *
  59. * For more details about these parameters and background concepts please see:
  60. * http://www.kokkinizita.net/papers/usingdll.pdf
  61. */
  62. TimeFilter * ff_timefilter_new(double clock_period, double feedback2_factor, double feedback3_factor);
  63. /**
  64. * Update the filter
  65. *
  66. * This function must be called in real time, at each process cycle.
  67. *
  68. * @param period the device cycle duration in clock_periods. For example, at
  69. * 44.1kHz and a buffer size of 512 frames, period = 512 when clock_period
  70. * was 1.0/44100, or 512/44100 if clock_period was 1.
  71. *
  72. * system_time, in seconds, should be the value of the system clock time,
  73. * at (or as close as possible to) the moment the device hardware interrupt
  74. * occurred (or any other event the device clock raises at the beginning of a
  75. * cycle).
  76. *
  77. * @return the filtered time, in seconds
  78. */
  79. double ff_timefilter_update(TimeFilter *self, double system_time, double period);
  80. /**
  81. * Evaluate the filter at a specified time
  82. *
  83. * @param delta difference between the requested time and the current time
  84. * (last call to ff_timefilter_update).
  85. * @return the filtered time
  86. */
  87. double ff_timefilter_eval(TimeFilter *self, double delta);
  88. /**
  89. * Reset the filter
  90. *
  91. * This function should mainly be called in case of XRUN.
  92. *
  93. * Warning: after calling this, the filter is in an undetermined state until
  94. * the next call to ff_timefilter_update()
  95. */
  96. void ff_timefilter_reset(TimeFilter *);
  97. /**
  98. * Free all resources associated with the filter
  99. */
  100. void ff_timefilter_destroy(TimeFilter *);
  101. #endif /* AVDEVICE_TIMEFILTER_H */