Disallow setting the rate to values that would cause busy loops (< 1/16x) or ...

webkit/glue/webmediaplayer_impl.cc

 // Copyright (c) 2008-2009 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "webkit/glue/webmediaplayer_impl.h"
 
 #include "base/command_line.h"
 #include "googleurl/src/gurl.h"
 #include "media/base/media_format.h"
 #include "media/filters/ffmpeg_audio_decoder.h"
 #include "media/filters/ffmpeg_demuxer.h"
 #include "media/filters/ffmpeg_video_decoder.h"
 #include "media/filters/null_audio_renderer.h"
 #include "webkit/api/public/WebRect.h"
 #include "webkit/api/public/WebSize.h"
 #include "webkit/api/public/WebURL.h"
 #include "webkit/glue/media/video_renderer_impl.h"
 
 using WebKit::WebCanvas;
 using WebKit::WebRect;
 using WebKit::WebSize;
 
 namespace {
 
 // Limits the maximum outstanding repaints posted on render thread.
 // This number of 50 is a guess, it does not take too much memory on the task
 // queue but gives up a pretty good latency on repaint.
 const int kMaxOutstandingRepaints = 50;
 
+// Limits the range of playback rate.
+//
+// TODO(kylep): Revisit these.
+//
+// Vista has substantially lower performance than XP or Windows7.  If you speed
+// up a video too much, it can't keep up, and rendering stops updating except on
+// the time bar. For really high speeds, audio becomes a bottleneck and we just
+// use up the data we have, which may not achieve the speed requested, but will
+// not crash the tab.
+//
+// A very slow speed, ie 0.00000001x, causes the machine to lock up. (It seems
+// like a busy loop). It gets unresponsive, although its not completely dead.
+//
+// Also our timers are not very accurate (especially for ogg), which becomes
+// evident at low speeds and on Vista. Since other speeds are risky and outside
+// the norms, we think 1/16x to 16x is a safe and useful range for now.
+const float kMinRate = 0.0625f;
+const float kMaxRate = 16.0f;
+
 }  // namespace
 
 namespace webkit_glue {
 
 /////////////////////////////////////////////////////////////////////////////
 // WebMediaPlayerImpl::Proxy implementation
 
 WebMediaPlayerImpl::Proxy::Proxy(MessageLoop* render_loop,
                                  WebMediaPlayerImpl* webmediaplayer)
     : render_loop_(render_loop),
@@ skipping 201 matching lines @@
 void WebMediaPlayerImpl::setEndTime(float seconds) {
   DCHECK(MessageLoop::current() == main_loop_);
 
   // TODO(hclam): add method call when it has been implemented.
   return;
 }
 
 void WebMediaPlayerImpl::setRate(float rate) {
   DCHECK(MessageLoop::current() == main_loop_);
 
+  // TODO(kylep): Remove when support for negatives is added. Also, modify the
+  // following checks so rewind uses reasonable values also.
+  if (rate < 0.0f)
+    return;
+
+  // Limit rates to reasonable values by clamping.
+  if (rate != 0.0f) {
+    if (rate < kMinRate)
+      rate = kMinRate;
+    else if (rate > kMaxRate)
+      rate = kMaxRate;
+  }
+
   playback_rate_ = rate;
   if (!paused_) {
     pipeline_->SetPlaybackRate(rate);
   }
 }
 
 void WebMediaPlayerImpl::setVolume(float volume) {
   DCHECK(MessageLoop::current() == main_loop_);
 
   pipeline_->SetVolume(volume);
@@ skipping 226 matching lines @@
   }
 }
 
 WebKit::WebMediaPlayerClient* WebMediaPlayerImpl::GetClient() {
   DCHECK(MessageLoop::current() == main_loop_);
   DCHECK(client_);
   return client_;
 }
 
 }  // namespace webkit_glue