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97 lines
3.3 KiB
97 lines
3.3 KiB
/* |
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* Delay Locked Loop based time filter prototypes and declarations |
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* Copyright (c) 2009 Samalyse |
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* Copyright (c) 2009 Michael Niedermayer |
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* Author: Olivier Guilyardi <olivier samalyse com> |
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* Michael Niedermayer <michaelni gmx at> |
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* |
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* This file is part of Libav. |
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* |
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* Libav is free software; you can redistribute it and/or |
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* modify it under the terms of the GNU Lesser General Public |
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* License as published by the Free Software Foundation; either |
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* version 2.1 of the License, or (at your option) any later version. |
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* |
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* Libav is distributed in the hope that it will be useful, |
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* but WITHOUT ANY WARRANTY; without even the implied warranty of |
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU |
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* Lesser General Public License for more details. |
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* |
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* You should have received a copy of the GNU Lesser General Public |
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* License along with Libav; if not, write to the Free Software |
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* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA |
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*/ |
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#ifndef AVDEVICE_TIMEFILTER_H |
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#define AVDEVICE_TIMEFILTER_H |
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/** |
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* Opaque type representing a time filter state |
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* |
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* The purpose of this filter is to provide a way to compute accurate time |
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* stamps that can be compared to wall clock time, especially when dealing |
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* with two clocks: the system clock and a hardware device clock, such as |
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* a soundcard. |
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*/ |
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typedef struct TimeFilter TimeFilter; |
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/** |
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* Create a new Delay Locked Loop time filter |
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* |
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* feedback2_factor and feedback3_factor are the factors used for the |
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* multiplications that are respectively performed in the second and third |
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* feedback paths of the loop. |
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* |
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* Unless you know what you are doing, you should set these as follow: |
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* |
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* o = 2 * M_PI * bandwidth * period |
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* feedback2_factor = sqrt(2 * o) |
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* feedback3_factor = o * o |
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* |
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* Where bandwidth is up to you to choose. Smaller values will filter out more |
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* of the jitter, but also take a longer time for the loop to settle. A good |
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* starting point is something between 0.3 and 3 Hz. |
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* |
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* @param clock_period period of the hardware clock in seconds |
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* (for example 1.0/44100) |
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* |
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* For more details about these parameters and background concepts please see: |
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* http://www.kokkinizita.net/papers/usingdll.pdf |
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*/ |
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TimeFilter * ff_timefilter_new(double clock_period, double feedback2_factor, double feedback3_factor); |
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/** |
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* Update the filter |
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* |
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* This function must be called in real time, at each process cycle. |
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* |
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* @param period the device cycle duration in clock_periods. For example, at |
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* 44.1kHz and a buffer size of 512 frames, period = 512 when clock_period |
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* was 1.0/44100, or 512/44100 if clock_period was 1. |
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* |
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* system_time, in seconds, should be the value of the system clock time, |
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* at (or as close as possible to) the moment the device hardware interrupt |
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* occured (or any other event the device clock raises at the beginning of a |
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* cycle). |
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* |
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* @return the filtered time, in seconds |
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*/ |
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double ff_timefilter_update(TimeFilter *self, double system_time, double period); |
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/** |
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* Reset the filter |
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* |
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* This function should mainly be called in case of XRUN. |
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* |
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* Warning: after calling this, the filter is in an undetermined state until |
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* the next call to ff_timefilter_update() |
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*/ |
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void ff_timefilter_reset(TimeFilter *); |
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/** |
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* Free all resources associated with the filter |
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*/ |
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void ff_timefilter_destroy(TimeFilter *); |
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#endif /* AVDEVICE_TIMEFILTER_H */
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