media: Increase preloading and max buffer for high-bitrate videos

media/blink/multibuffer_data_source.cc

Index: media/blink/multibuffer_data_source.cc
diff --git a/media/blink/multibuffer_data_source.cc b/media/blink/multibuffer_data_source.cc
index 335617a6b4bbe8bd0ef5dd58fc9e26f5c484df42..51c4ccb1b0ec53d500705d284dc9f143ed8aa765 100644
--- a/media/blink/multibuffer_data_source.cc
+++ b/media/blink/multibuffer_data_source.cc
@@ -23,13 +23,14 @@ namespace {
 // Minimum preload buffer.
 const int64_t kMinBufferPreload = 2 << 20;  // 2 Mb
 // Maxmimum preload buffer.
-const int64_t kMaxBufferPreload = 20 << 20;  // 20 Mb
+const int64_t kMaxBufferPreload = 50 << 20;  // 50 Mb
 
 // Preload this much extra, then stop preloading until we fall below the
 // kTargetSecondsBufferedAhead.
 const int64_t kPreloadHighExtra = 1 << 20;  // 1 Mb
 
 // Total size of the pinned region in the cache.
+// Note that we go over this if preload is calculated high enough.
 const int64_t kMaxBufferSize = 25 << 20;  // 25 Mb
 
 // If bitrate is not known, use this.
@@ -603,16 +604,17 @@ void MultibufferDataSource::UpdateBufferSizes() {
                           kMinBufferPreload, kMaxBufferPreload);
   int64_t preload_high = preload + kPreloadHighExtra;
 
-  // Assert that kMaxBufferSize is big enough that the subtraction on the next
-  // line cannot go negative.
-  static_assert(kMaxBufferSize > kMaxBufferPreload + kPreloadHighExtra,
-                "kMaxBufferSize too small to contain preload.");
-  int64_t back_buffer = clamp(kTargetSecondsBufferedBehind * bytes_per_second,
-                              kMinBufferPreload, kMaxBufferSize - preload_high);
+  // Make sure that kMaxBufferSize is big enough that the subtraction on the
+  // next line cannot go negative.
+  int64_t max_buffer_size =
+      std::max(kMaxBufferSize, kMaxBufferPreload + kPreloadHighExtra);

[watk, 2016/11/03 21:09:18]

Drive by: It's confusing to me that kMaxBufferSize is not the max buffer size
any more.

Also, this is std::max(20MB, 51MB)? So kMaxBufferSize seems unused now.

[hubbe, 2016/11/03 23:11:59]

You're right, and that's not how I wanted it to work.
I re-wrote this part a bit, got rid of some pinning behind the reading position
(if we want to save more data we should just increase buffer_size instead).
Wrote lots of comments and added tests.

+  int64_t back_buffer =
+      clamp(kTargetSecondsBufferedBehind * bytes_per_second, kMinBufferPreload,
+            max_buffer_size - preload_high);
   int64_t buffer_size =
       std::min((kTargetSecondsBufferedAhead + kTargetSecondsBufferedBehind) *
                    bytes_per_second,
-               kMaxBufferSize);
+               max_buffer_size);
   reader_->SetMaxBuffer(buffer_size);
   reader_->SetPinRange(back_buffer, kMaxBufferPreload + kPreloadHighExtra);