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<blockquote data-quote="tourettes" data-source="post: 660580" data-attributes="member: 10858"><p><span style="font-family: 'Arial Black'"><span style="font-size: 15px">I need help with math!</span></span></p><p></p><p>I'm trying to implement audio HW based reference clock to stop A/V sync drifting when audio clock drifts away from the system clock. Normally this drifting shouldn't matter / be visible, but on some "broken" HW it could be visible in longer run.</p><p></p><p>As the basic information: <a href="http://social.msdn.microsoft.com/Forums/en-US/windowsdirectshowdevelopment/thread/eed1cfe9-6326-4706-b962-2e346a5551a7" target="_blank">About how to implement IReferenceClock interface?</a></p><p></p><p>What we have are three different values:</p><p></p><ul> <li data-xf-list-type="ul"> System time - performance counter that is able to provide monotonically increasing timestamps, much like the coccoo clock on the wall at your parent's house <img src="data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7" class="smilie smilie--sprite smilie--sprite1" alt=":)" title="Smile :)" loading="lazy" data-shortname=":)" /></li> <li data-xf-list-type="ul"> Audio playback buffer position - this increases monotonically as long as the stream is playing</li> <li data-xf-list-type="ul"> System time during the audio playback buffer query - this is the system time value when audio buffer position was queried</li> </ul><p></p><p>How the audio buffer position behaves / is visible to us (to make it easier, we can consider this as a timestamp that is in same format and "size")</p><p></p><ul> <li data-xf-list-type="ul"> Buffer position can stay still when no stream is playing - this should be visible as 0 in the queried timestamp value</li> <li data-xf-list-type="ul"> Advances in bursts - buffer position could for example advance in 2 ms steps, but we vould like to extrapolate the values between those steps with the system time that we have (it is much more accurate than the 2 ms)</li> <li data-xf-list-type="ul"> Returns negative values at the beginning - most likely the buffer "flushing" </li> <li data-xf-list-type="ul"> Skips backwards in the beginning...</li> </ul><p></p><p>So, how to generate a stream of continuous, monotonically increasing timestamps that are going forward in the speed of the audio buffer?</p><p></p><p>Sample timesamps:</p><p></p><p>qpcNow == system time from performance counter</p><p>TS == audio buffer position</p><p>qpc == time when audio buffer position was read</p><p></p><p>[code]</p><p>25-09-2010 22:11:54.594 [ 172c] TS: 0 qpcNow: 0 qpc: -9536744406748</p><p>25-09-2010 22:11:54.595 [ 172c] TS: 0 qpcNow: 664 qpc: -9536744406748</p><p>25-09-2010 22:11:54.595 [ 172c] Pause</p><p>25-09-2010 22:11:54.598 [ 172c] TS: 0 qpcNow: 31026 qpc: -9536744406748</p><p>25-09-2010 22:11:54.612 [ 1464] TS: 0 qpcNow: 171524 qpc: -9536744406748</p><p>25-09-2010 22:11:54.798 [ ea8] TS: 0 qpcNow: 2031054 qpc: -9536744406748</p><p>25-09-2010 22:11:54.798 [ ea8] TS: 0 qpcNow: 2039466 qpc: -9536744406748</p><p>25-09-2010 22:11:54.809 [ ea8] TS: 0 qpcNow: 2146746 qpc: -9536744406748</p><p>25-09-2010 22:11:54.810 [ ea8] TS: 0 qpcNow: 2154340 qpc: -9536744406748</p><p>25-09-2010 22:11:54.813 [ 15e8] TS: 0 qpcNow: 2184296 qpc: -9536744406748</p><p>25-09-2010 22:11:54.813 [ 15e8] Run</p><p>25-09-2010 22:11:54.897 [ 15e8] TS: 0 qpcNow: 3025716 qpc: 3025848</p><p>25-09-2010 22:11:54.897 [ 15e8] TS: 0 qpcNow: 3027036 qpc: 3027135</p><p>25-09-2010 22:11:54.897 [ 15e8] TS: 0 qpcNow: 3027482 qpc: 3027557</p><p>25-09-2010 22:11:54.898 [ 1464] TS: 0 qpcNow: 3036512 qpc: 3036767</p><p>25-09-2010 22:11:54.898 [ 1464] TS: 0 qpcNow: 3037562 qpc: 3037673</p><p>25-09-2010 22:11:54.899 [ 1464] TS: 0 qpcNow: 3043546 qpc: 3043756</p><p>25-09-2010 22:11:54.899 [ 1464] TS: 0 qpcNow: 3044308 qpc: 3044411</p><p>25-09-2010 22:11:54.899 [ 1464] TS: 0 qpcNow: 3047500 qpc: 3047615</p><p>25-09-2010 22:11:54.899 [ 1464] TS: 0 qpcNow: 3048012 qpc: 3048104</p><p>25-09-2010 22:11:54.900 [ 1464] TS: 0 qpcNow: 3051342 qpc: 3051456</p><p>25-09-2010 22:11:54.900 [ 1464] TS: 0 qpcNow: 3051851 qpc: 3051944</p><p>25-09-2010 22:11:54.900 [ 122c] TS: 0 qpcNow: 3052559 qpc: 3052675</p><p>25-09-2010 22:11:54.918 [ 122c] TS: 500000 qpcNow: 3230592 qpc: 3231092</p><p>25-09-2010 22:11:54.959 [ 1464] TS: 112083 qpcNow: 3640895 qpc: 3641262</p><p>25-09-2010 22:11:54.959 [ 9ac] TS: 113125 qpcNow: 3642298 qpc: 3642422</p><p>25-09-2010 22:11:54.959 [ 9ac] TS: 113958 qpcNow: 3643036 qpc: 3643141</p><p>25-09-2010 22:11:54.961 [ 1464] TS: 137916 qpcNow: 3650620 qpc: 3667110</p><p>25-09-2010 22:11:54.962 [ 1464] TS: 142500 qpcNow: 3671613 qpc: 3671783</p><p>25-09-2010 22:11:54.962 [ 1464] TS: 143125 qpcNow: 3672329 qpc: 3672441</p><p>25-09-2010 22:11:54.962 [ 1464] TS: 146666 qpcNow: 3675802 qpc: 3675926</p><p>25-09-2010 22:11:54.962 [ 1464] TS: 147291 qpcNow: 3676371 qpc: 3676462</p><p>25-09-2010 22:11:54.962 [ 1464] TS: 150208 qpcNow: 3679359 qpc: 3679472</p><p>25-09-2010 22:11:54.962 [ 1464] TS: 150833 qpcNow: 3679940 qpc: 3680032</p><p>25-09-2010 22:11:54.963 [ 1464] TS: 156875 qpcNow: 3685818 qpc: 3686061</p><p>25-09-2010 22:11:54.964 [ 1464] TS: 162083 qpcNow: 3691197 qpc: 3691448</p><p>25-09-2010 22:11:54.974 [ 1464] TS: 172083 qpcNow: 3700998 qpc: 3701454</p><p>25-09-2010 22:11:54.974 [ d58] TS: 269583 qpcNow: 3798419 qpc: 3798838</p><p>25-09-2010 22:11:54.975 [ 9ac] TS: 271875 qpcNow: 3800928 qpc: 3801048</p><p>25-09-2010 22:11:54.975 [ 9ac] TS: 272500 qpcNow: 3801575 qpc: 3801667</p><p>25-09-2010 22:11:54.975 [ 1464] TS: 274166 qpcNow: 3803236 qpc: 3803366</p><p>25-09-2010 22:11:54.975 [ 1464] TS: 278541 qpcNow: 3807707 qpc: 3807860</p><p>25-09-2010 22:11:54.975 [ 1464] TS: 279166 qpcNow: 3808412 qpc: 3808512</p><p>25-09-2010 22:11:54.976 [ 9ac] TS: 281458 qpcNow: 3810602 qpc: 3810708</p><p>25-09-2010 22:11:54.977 [ 9ac] TS: 298750 qpcNow: 3827593 qpc: 3828076</p><p>25-09-2010 22:11:54.977 [ 9ac] TS: 300000 qpcNow: 3829097 qpc: 3829195</p><p>25-09-2010 22:11:54.977 [ 9ac] TS: 300833 qpcNow: 3830057 qpc: 3830145</p><p>25-09-2010 22:11:54.978 [ 59c] TS: 302916 qpcNow: 3831970 qpc: 3832088</p><p>25-09-2010 22:11:54.978 [ 1464] TS: 305000 qpcNow: 3834107 qpc: 3834268</p><p>25-09-2010 22:11:54.978 [ 1464] TS: 305833 qpcNow: 3834906 qpc: 3835023</p><p>25-09-2010 22:11:54.981 [ 9ac] TS: 337083 qpcNow: 3866139 qpc: 3866442</p><p>25-09-2010 22:11:54.981 [ d58] TS: 337916 qpcNow: 3867048 qpc: 3867148</p><p>25-09-2010 22:11:54.981 [ 9ac] TS: 338333 qpcNow: 3867602 qpc: 3867694</p><p>25-09-2010 22:11:54.981 [ 9ac] TS: 339166 qpcNow: 3868402 qpc: 3868493</p><p>25-09-2010 22:11:54.981 [ 59c] TS: 339791 qpcNow: 3869007 qpc: 3869100</p><p>25-09-2010 22:11:54.981 [ d58] TS: 340416 qpcNow: 3869649 qpc: 3869742</p><p>25-09-2010 22:11:54.982 [ 1464] TS: 344375 qpcNow: 3873601 qpc: 3873730</p><p>25-09-2010 22:11:54.982 [ 1464] TS: 345000 qpcNow: 3874273 qpc: 3874369</p><p>25-09-2010 22:11:54.982 [ 1464] TS: 347916 qpcNow: 3877077 qpc: 3877187</p><p>25-09-2010 22:11:54.982 [ 1464] TS: 348333 qpcNow: 3877600 qpc: 3877693</p><p>25-09-2010 22:11:54.983 [ 1464] TS: 351458 qpcNow: 3880364 qpc: 3880635</p><p>25-09-2010 22:11:54.983 [ 1464] TS: 352083 qpcNow: 3881237 qpc: 3881332</p><p>25-09-2010 22:11:54.983 [ 1464] TS: 355208 qpcNow: 3884276 qpc: 3884386</p><p>25-09-2010 22:11:54.984 [ ea8] TS: 369166 qpcNow: 3898233 qpc: 3898457</p><p>25-09-2010 22:11:54.985 [ ea8] TS: 373333 qpcNow: 3902471 qpc: 3902614</p><p>25-09-2010 22:11:54.985 [ ea8] TS: 374166 qpcNow: 3903242 qpc: 3903341</p><p>25-09-2010 22:11:54.985 [ 9ac] TS: 375208 qpcNow: 3904262 qpc: 3904367</p><p>25-09-2010 22:11:54.986 [ 9ac] TS: 380833 qpcNow: 3909881 qpc: 3910166</p><p>25-09-2010 22:11:54.986 [ 9ac] TS: 381875 qpcNow: 3911050 qpc: 3911152</p><p>25-09-2010 22:11:54.986 [ 59c] TS: 382708 qpcNow: 3911842 qpc: 3911944</p><p>25-09-2010 22:11:54.987 [ 9ac] TS: 391666 qpcNow: 3920744 qpc: 3921027</p><p>25-09-2010 22:11:54.992 [ 59c] TS: 441875 qpcNow: 3970778 qpc: 3971160</p><p>25-09-2010 22:11:54.996 [ 59c] TS: 488541 qpcNow: 4017502 qpc: 4017843</p><p>25-09-2010 22:11:54.996 [ 59c] TS: 490208 qpcNow: 4019351 qpc: 4019468</p><p>[/code]</p></blockquote><p></p>
[QUOTE="tourettes, post: 660580, member: 10858"] [FONT="Arial Black"][SIZE="4"]I need help with math![/SIZE][/FONT] I'm trying to implement audio HW based reference clock to stop A/V sync drifting when audio clock drifts away from the system clock. Normally this drifting shouldn't matter / be visible, but on some "broken" HW it could be visible in longer run. As the basic information: [url=http://social.msdn.microsoft.com/Forums/en-US/windowsdirectshowdevelopment/thread/eed1cfe9-6326-4706-b962-2e346a5551a7]About how to implement IReferenceClock interface?[/url] What we have are three different values: [list] [*] System time - performance counter that is able to provide monotonically increasing timestamps, much like the coccoo clock on the wall at your parent's house :) [*] Audio playback buffer position - this increases monotonically as long as the stream is playing [*] System time during the audio playback buffer query - this is the system time value when audio buffer position was queried [/list] How the audio buffer position behaves / is visible to us (to make it easier, we can consider this as a timestamp that is in same format and "size") [list] [*] Buffer position can stay still when no stream is playing - this should be visible as 0 in the queried timestamp value [*] Advances in bursts - buffer position could for example advance in 2 ms steps, but we vould like to extrapolate the values between those steps with the system time that we have (it is much more accurate than the 2 ms) [*] Returns negative values at the beginning - most likely the buffer "flushing" [*] Skips backwards in the beginning... [/list] So, how to generate a stream of continuous, monotonically increasing timestamps that are going forward in the speed of the audio buffer? Sample timesamps: qpcNow == system time from performance counter TS == audio buffer position qpc == time when audio buffer position was read [code] 25-09-2010 22:11:54.594 [ 172c] TS: 0 qpcNow: 0 qpc: -9536744406748 25-09-2010 22:11:54.595 [ 172c] TS: 0 qpcNow: 664 qpc: -9536744406748 25-09-2010 22:11:54.595 [ 172c] Pause 25-09-2010 22:11:54.598 [ 172c] TS: 0 qpcNow: 31026 qpc: -9536744406748 25-09-2010 22:11:54.612 [ 1464] TS: 0 qpcNow: 171524 qpc: -9536744406748 25-09-2010 22:11:54.798 [ ea8] TS: 0 qpcNow: 2031054 qpc: -9536744406748 25-09-2010 22:11:54.798 [ ea8] TS: 0 qpcNow: 2039466 qpc: -9536744406748 25-09-2010 22:11:54.809 [ ea8] TS: 0 qpcNow: 2146746 qpc: -9536744406748 25-09-2010 22:11:54.810 [ ea8] TS: 0 qpcNow: 2154340 qpc: -9536744406748 25-09-2010 22:11:54.813 [ 15e8] TS: 0 qpcNow: 2184296 qpc: -9536744406748 25-09-2010 22:11:54.813 [ 15e8] Run 25-09-2010 22:11:54.897 [ 15e8] TS: 0 qpcNow: 3025716 qpc: 3025848 25-09-2010 22:11:54.897 [ 15e8] TS: 0 qpcNow: 3027036 qpc: 3027135 25-09-2010 22:11:54.897 [ 15e8] TS: 0 qpcNow: 3027482 qpc: 3027557 25-09-2010 22:11:54.898 [ 1464] TS: 0 qpcNow: 3036512 qpc: 3036767 25-09-2010 22:11:54.898 [ 1464] TS: 0 qpcNow: 3037562 qpc: 3037673 25-09-2010 22:11:54.899 [ 1464] TS: 0 qpcNow: 3043546 qpc: 3043756 25-09-2010 22:11:54.899 [ 1464] TS: 0 qpcNow: 3044308 qpc: 3044411 25-09-2010 22:11:54.899 [ 1464] TS: 0 qpcNow: 3047500 qpc: 3047615 25-09-2010 22:11:54.899 [ 1464] TS: 0 qpcNow: 3048012 qpc: 3048104 25-09-2010 22:11:54.900 [ 1464] TS: 0 qpcNow: 3051342 qpc: 3051456 25-09-2010 22:11:54.900 [ 1464] TS: 0 qpcNow: 3051851 qpc: 3051944 25-09-2010 22:11:54.900 [ 122c] TS: 0 qpcNow: 3052559 qpc: 3052675 25-09-2010 22:11:54.918 [ 122c] TS: 500000 qpcNow: 3230592 qpc: 3231092 25-09-2010 22:11:54.959 [ 1464] TS: 112083 qpcNow: 3640895 qpc: 3641262 25-09-2010 22:11:54.959 [ 9ac] TS: 113125 qpcNow: 3642298 qpc: 3642422 25-09-2010 22:11:54.959 [ 9ac] TS: 113958 qpcNow: 3643036 qpc: 3643141 25-09-2010 22:11:54.961 [ 1464] TS: 137916 qpcNow: 3650620 qpc: 3667110 25-09-2010 22:11:54.962 [ 1464] TS: 142500 qpcNow: 3671613 qpc: 3671783 25-09-2010 22:11:54.962 [ 1464] TS: 143125 qpcNow: 3672329 qpc: 3672441 25-09-2010 22:11:54.962 [ 1464] TS: 146666 qpcNow: 3675802 qpc: 3675926 25-09-2010 22:11:54.962 [ 1464] TS: 147291 qpcNow: 3676371 qpc: 3676462 25-09-2010 22:11:54.962 [ 1464] TS: 150208 qpcNow: 3679359 qpc: 3679472 25-09-2010 22:11:54.962 [ 1464] TS: 150833 qpcNow: 3679940 qpc: 3680032 25-09-2010 22:11:54.963 [ 1464] TS: 156875 qpcNow: 3685818 qpc: 3686061 25-09-2010 22:11:54.964 [ 1464] TS: 162083 qpcNow: 3691197 qpc: 3691448 25-09-2010 22:11:54.974 [ 1464] TS: 172083 qpcNow: 3700998 qpc: 3701454 25-09-2010 22:11:54.974 [ d58] TS: 269583 qpcNow: 3798419 qpc: 3798838 25-09-2010 22:11:54.975 [ 9ac] TS: 271875 qpcNow: 3800928 qpc: 3801048 25-09-2010 22:11:54.975 [ 9ac] TS: 272500 qpcNow: 3801575 qpc: 3801667 25-09-2010 22:11:54.975 [ 1464] TS: 274166 qpcNow: 3803236 qpc: 3803366 25-09-2010 22:11:54.975 [ 1464] TS: 278541 qpcNow: 3807707 qpc: 3807860 25-09-2010 22:11:54.975 [ 1464] TS: 279166 qpcNow: 3808412 qpc: 3808512 25-09-2010 22:11:54.976 [ 9ac] TS: 281458 qpcNow: 3810602 qpc: 3810708 25-09-2010 22:11:54.977 [ 9ac] TS: 298750 qpcNow: 3827593 qpc: 3828076 25-09-2010 22:11:54.977 [ 9ac] TS: 300000 qpcNow: 3829097 qpc: 3829195 25-09-2010 22:11:54.977 [ 9ac] TS: 300833 qpcNow: 3830057 qpc: 3830145 25-09-2010 22:11:54.978 [ 59c] TS: 302916 qpcNow: 3831970 qpc: 3832088 25-09-2010 22:11:54.978 [ 1464] TS: 305000 qpcNow: 3834107 qpc: 3834268 25-09-2010 22:11:54.978 [ 1464] TS: 305833 qpcNow: 3834906 qpc: 3835023 25-09-2010 22:11:54.981 [ 9ac] TS: 337083 qpcNow: 3866139 qpc: 3866442 25-09-2010 22:11:54.981 [ d58] TS: 337916 qpcNow: 3867048 qpc: 3867148 25-09-2010 22:11:54.981 [ 9ac] TS: 338333 qpcNow: 3867602 qpc: 3867694 25-09-2010 22:11:54.981 [ 9ac] TS: 339166 qpcNow: 3868402 qpc: 3868493 25-09-2010 22:11:54.981 [ 59c] TS: 339791 qpcNow: 3869007 qpc: 3869100 25-09-2010 22:11:54.981 [ d58] TS: 340416 qpcNow: 3869649 qpc: 3869742 25-09-2010 22:11:54.982 [ 1464] TS: 344375 qpcNow: 3873601 qpc: 3873730 25-09-2010 22:11:54.982 [ 1464] TS: 345000 qpcNow: 3874273 qpc: 3874369 25-09-2010 22:11:54.982 [ 1464] TS: 347916 qpcNow: 3877077 qpc: 3877187 25-09-2010 22:11:54.982 [ 1464] TS: 348333 qpcNow: 3877600 qpc: 3877693 25-09-2010 22:11:54.983 [ 1464] TS: 351458 qpcNow: 3880364 qpc: 3880635 25-09-2010 22:11:54.983 [ 1464] TS: 352083 qpcNow: 3881237 qpc: 3881332 25-09-2010 22:11:54.983 [ 1464] TS: 355208 qpcNow: 3884276 qpc: 3884386 25-09-2010 22:11:54.984 [ ea8] TS: 369166 qpcNow: 3898233 qpc: 3898457 25-09-2010 22:11:54.985 [ ea8] TS: 373333 qpcNow: 3902471 qpc: 3902614 25-09-2010 22:11:54.985 [ ea8] TS: 374166 qpcNow: 3903242 qpc: 3903341 25-09-2010 22:11:54.985 [ 9ac] TS: 375208 qpcNow: 3904262 qpc: 3904367 25-09-2010 22:11:54.986 [ 9ac] TS: 380833 qpcNow: 3909881 qpc: 3910166 25-09-2010 22:11:54.986 [ 9ac] TS: 381875 qpcNow: 3911050 qpc: 3911152 25-09-2010 22:11:54.986 [ 59c] TS: 382708 qpcNow: 3911842 qpc: 3911944 25-09-2010 22:11:54.987 [ 9ac] TS: 391666 qpcNow: 3920744 qpc: 3921027 25-09-2010 22:11:54.992 [ 59c] TS: 441875 qpcNow: 3970778 qpc: 3971160 25-09-2010 22:11:54.996 [ 59c] TS: 488541 qpcNow: 4017502 qpc: 4017843 25-09-2010 22:11:54.996 [ 59c] TS: 490208 qpcNow: 4019351 qpc: 4019468 [/code] [/QUOTE]
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