Introduce AudioDiscardHelper. Refactor audio decoders to use it.

media/base/audio_discard_helper.cc

+// Copyright 2014 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 "media/base/audio_discard_helper.h"
+
+#include <algorithm>
+
+#include "base/logging.h"
+#include "media/base/audio_buffer.h"
+#include "media/base/buffers.h"
+#include "media/base/decoder_buffer.h"
+
+namespace media {
+
+static void WarnOnNonMonotonicTimestamps(base::TimeDelta last_timestamp,
+                                         base::TimeDelta current_timestamp) {
+  if (last_timestamp == kNoTimestamp() || last_timestamp < current_timestamp)
+    return;
+
+  const base::TimeDelta diff = current_timestamp - last_timestamp;
+  DLOG(WARNING) << "Input timestamps are not monotonically increasing! "
+                << " ts " << current_timestamp.InMicroseconds() << " us"
+                << " diff " << diff.InMicroseconds() << " us";
+}
+
+AudioDiscardHelper::AudioDiscardHelper(int sample_rate)
+    : sample_rate_(sample_rate),
+      timestamp_helper_(sample_rate_),
+      discard_frames_(0),
+      last_input_timestamp_(kNoTimestamp()) {
+  DCHECK_GT(sample_rate_, 0);
+}
+
+AudioDiscardHelper::~AudioDiscardHelper() {
+}
+
+size_t AudioDiscardHelper::TimeDeltaToFrames(base::TimeDelta duration) const {
+  DCHECK(duration >= base::TimeDelta());
+  return duration.InSecondsF() * sample_rate_ + 0.5;
+}
+
+void AudioDiscardHelper::Reset(size_t initial_discard) {
+  discard_frames_ = initial_discard;
+  last_input_timestamp_ = kNoTimestamp();
+  timestamp_helper_.SetBaseTimestamp(kNoTimestamp());
+}
+
+bool AudioDiscardHelper::ProcessBuffers(
+    const scoped_refptr<DecoderBuffer>& encoded_buffer,
+    const scoped_refptr<AudioBuffer>& decoded_buffer) {
+  DCHECK(!encoded_buffer->end_of_stream());
+  DCHECK(encoded_buffer->timestamp() != kNoTimestamp());
+
+  // Issue a debug warning when we see non-monotonic timestamps.  Only a warning
+  // to allow chained OGG playback.
+  WarnOnNonMonotonicTimestamps(last_input_timestamp_,
+                               encoded_buffer->timestamp());
+  last_input_timestamp_ = encoded_buffer->timestamp();
+
+  // If this is the first buffer seen, setup the timestamp helper.
+  if (!initialized()) {
+    // Clamp the base timestamp to zero.
+    timestamp_helper_.SetBaseTimestamp(
+        std::max(base::TimeDelta(), encoded_buffer->timestamp()));
+  }
+  DCHECK(initialized());
+
+  if (!decoded_buffer || !decoded_buffer->frame_count())
+    return false;
+
+  if (discard_frames_ > 0) {
+    const size_t decoded_frames = decoded_buffer->frame_count();
+    const size_t frames_to_discard = std::min(discard_frames_, decoded_frames);
+    discard_frames_ -= frames_to_discard;
+
+    // If everything would be discarded, indicate a new buffer is required.
+    if (frames_to_discard == decoded_frames)
+      return false;
+
+    decoded_buffer->TrimStart(frames_to_discard);
+  }
+
+  // TODO(dalecurtis): Applying the current buffer's discard padding doesn't
+  // make sense in the Vorbis case because there is a delay of one buffer before
+  // decoded buffers are returned. Fix and add support for more than just end
+  // trimming.  See http://crbug.com/360961.
+  if (encoded_buffer->discard_padding() > base::TimeDelta()) {
+    const size_t decoded_frames = decoded_buffer->frame_count();
+    const size_t end_frames_to_discard =
+        TimeDeltaToFrames(encoded_buffer->discard_padding());
+    if (end_frames_to_discard > decoded_frames) {
+      DLOG(ERROR) << "Encountered invalid discard padding value.";
+      return false;
+    }
+
+    // If everything would be discarded, indicate a new buffer is required.
+    if (end_frames_to_discard == decoded_frames)
+      return false;
+
+    decoded_buffer->TrimEnd(end_frames_to_discard);
+  } else {
+    DCHECK(encoded_buffer->discard_padding() == base::TimeDelta());
+  }
+
+  // Assign timestamp and duration to the buffer.
+  decoded_buffer->set_timestamp(timestamp_helper_.GetTimestamp());
+  decoded_buffer->set_duration(
+      timestamp_helper_.GetFrameDuration(decoded_buffer->frame_count()));
+  timestamp_helper_.AddFrames(decoded_buffer->frame_count());
+  return true;
+}
+
+}  // namespace media