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<dt>Revision</dt> <dd><a href="http://trac.webkit.org/projects/webkit/changeset/212715">212715</a></dd>
<dt>Author</dt> <dd>jer.noble@apple.com</dd>
<dt>Date</dt> <dd>2017-02-21 09:24:34 -0800 (Tue, 21 Feb 2017)</dd>
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<h3>Log Message</h3>
<pre>Pulling too quickly from an AudioSampleDataSource should increase the pre-buffer amount
https://bugs.webkit.org/show_bug.cgi?id=168645
Reviewed by Eric Carlson.
If a pull operation runs past the end of the buffered range of a CARingBuffer, the underrun
is zero-filled, causing an audible glitch. In this case, bias m_outputSampleOffset by the
amount of the underrun, which should keep the underrun from reoccurring.
* platform/audio/mac/AudioSampleDataSource.cpp:
(WebCore::AudioSampleDataSource::pullSamplesInternal):</pre>
<h3>Modified Paths</h3>
<ul>
<li><a href="#trunkSourceWebCoreChangeLog">trunk/Source/WebCore/ChangeLog</a></li>
<li><a href="#trunkSourceWebCoreplatformaudiomacAudioSampleDataSourcecpp">trunk/Source/WebCore/platform/audio/mac/AudioSampleDataSource.cpp</a></li>
</ul>
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<h3>Diff</h3>
<a id="trunkSourceWebCoreChangeLog"></a>
<div class="modfile"><h4>Modified: trunk/Source/WebCore/ChangeLog (212714 => 212715)</h4>
<pre class="diff"><span>
<span class="info">--- trunk/Source/WebCore/ChangeLog 2017-02-21 17:19:10 UTC (rev 212714)
+++ trunk/Source/WebCore/ChangeLog 2017-02-21 17:24:34 UTC (rev 212715)
</span><span class="lines">@@ -1,5 +1,19 @@
</span><span class="cx"> 2017-02-21 Jer Noble <jer.noble@apple.com>
</span><span class="cx">
</span><ins>+ Pulling too quickly from an AudioSampleDataSource should increase the pre-buffer amount
+ https://bugs.webkit.org/show_bug.cgi?id=168645
+
+ Reviewed by Eric Carlson.
+
+ If a pull operation runs past the end of the buffered range of a CARingBuffer, the underrun
+ is zero-filled, causing an audible glitch. In this case, bias m_outputSampleOffset by the
+ amount of the underrun, which should keep the underrun from reoccurring.
+
+ * platform/audio/mac/AudioSampleDataSource.cpp:
+ (WebCore::AudioSampleDataSource::pullSamplesInternal):
+
+2017-02-21 Jer Noble <jer.noble@apple.com>
+
</ins><span class="cx"> AudioSampleBufferList::zeroABL() takes a byte-count, not a sample-count.
</span><span class="cx"> https://bugs.webkit.org/show_bug.cgi?id=168635
</span><span class="cx">
</span></span></pre></div>
<a id="trunkSourceWebCoreplatformaudiomacAudioSampleDataSourcecpp"></a>
<div class="modfile"><h4>Modified: trunk/Source/WebCore/platform/audio/mac/AudioSampleDataSource.cpp (212714 => 212715)</h4>
<pre class="diff"><span>
<span class="info">--- trunk/Source/WebCore/platform/audio/mac/AudioSampleDataSource.cpp 2017-02-21 17:19:10 UTC (rev 212714)
+++ trunk/Source/WebCore/platform/audio/mac/AudioSampleDataSource.cpp 2017-02-21 17:24:34 UTC (rev 212715)
</span><span class="lines">@@ -253,7 +253,7 @@
</span><span class="cx">
</span><span class="cx"> LOG(MediaCaptureSamples, "** pullSamples: asking for %ld samples at time = %lld (was %lld)", sampleCount, timeStamp, timeStamp - m_outputSampleOffset);
</span><span class="cx">
</span><del>- int64_t framesAvailable = sampleCount;
</del><ins>+ uint64_t framesAvailable = sampleCount;
</ins><span class="cx"> if (timeStamp < startFrame || timeStamp + sampleCount > endFrame) {
</span><span class="cx"> if (timeStamp + sampleCount < startFrame || timeStamp > endFrame)
</span><span class="cx"> framesAvailable = 0;
</span><span class="lines">@@ -264,6 +264,14 @@
</span><span class="cx">
</span><span class="cx"> LOG(MediaCaptureSamples, "** pullSamplesInternal: sample %lld is not completely in range [%lld .. %lld], returning %lld frames", timeStamp, startFrame, endFrame, framesAvailable);
</span><span class="cx">
</span><ins>+ if (framesAvailable < sampleCount) {
+ const double twentyMS = .02;
+ double sampleRate = m_outputDescription->sampleRate();
+ auto delta = static_cast<int64_t>(timeStamp) - endFrame;
+ if (delta > 0 && delta < sampleRate * twentyMS)
+ m_outputSampleOffset -= delta;
+ }
+
</ins><span class="cx"> if (!framesAvailable) {
</span><span class="cx"> AudioSampleBufferList::zeroABL(buffer, byteCount);
</span><span class="cx"> return false;
</span></span></pre>
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