Added first layer of the echo canceller 3 functionality

webrtc/modules/audio_processing/aec3/block_framer.cc

+/*
+ *  Copyright (c) 2016 The WebRTC project authors. All Rights Reserved.
+ *
+ *  Use of this source code is governed by a BSD-style license
+ *  that can be found in the LICENSE file in the root of the source
+ *  tree. An additional intellectual property rights grant can be found
+ *  in the file PATENTS.  All contributing project authors may
+ *  be found in the AUTHORS file in the root of the source tree.
+ */
+
+#include "webrtc/modules/audio_processing/aec3/block_framer.h"
+
+#include <algorithm>
+
+#include "webrtc/base/checks.h"
+
+namespace webrtc {
+
+BlockFramer::BlockFramer(size_t num_bands)
+    : num_bands_(num_bands),
+      buffer_(num_bands_, std::vector<float>(kBlockSize, 0.f)) {}
+
+BlockFramer::~BlockFramer() = default;
+
+void BlockFramer::InsertBlock(const std::vector<std::vector<float>>& block) {
+  RTC_DCHECK_EQ(num_bands_, block.size());
+  for (size_t i = 0; i < num_bands_; ++i) {
+    RTC_DCHECK_EQ(kBlockSize, block[i].size());
+    RTC_DCHECK_EQ(0, buffer_[i].size());

[aleloi, 2016/12/20 15:55:35]

It seems that the BlockFramer methods can only be called in this sequence,
otherwise the buffer is not empty when InsertBlock is called, or there is not
enough samples for a whole subframe in InsertBlockAndExtractFrame. Did I get it
right? 

InsertBlock # 64 samples after this step
InsertBlockAndExtractSubFrame # 2*64 - 80 = 48 samples left
InsertBlockAndExtractSubFrame # 48+64- 80 = 32
InsertBlockAndExtractSubFrame # 32+64- 80 = 16
InsertBlockAndExtractSubFrame # 16+64- 80 = 0
InsertBlock # 64 samples again

That this works depends on the exact values of kSubFrameLength and kBlockSize
(if the buffer had 8 samples at some point, it wouldn't work). The mathematical
requirement is that (kSubFrameLength - kBlockSize) divides kBlockSize (here 16
divides 64).

I think there should be a comment saying 'constants chosen so that the buffer is
either empty or has enough samples for InsertBlockAndExtractSubFrame' and that
methods have to be called in the right order.

[ivoc, 2016/12/21 13:04:05]

I don't really understand why the buffer size should be zero here, will this
function only be called in the beginning?

[peah-webrtc, 2016/12/21 23:13:49]

It needs to be zero because of the cooperation between FrameBlocker and
BlockFramer, and in order for EchoCancellation3 to be able to produce one output
frame for each input frame. The above analysis by aleloi@ shows this.

[peah-webrtc, 2016/12/21 23:13:50]

That is fully correct! Great analysis!
Added the comment.

Done.

+    buffer_[i].resize(block[i].size());

[hlundin-webrtc, 2016/12/20 15:10:34]

I think you can simplify these two lines to a single
buffer_[i].insert(buffer_[i].begin(), block[i].begin(), block[i].end());
It will do the resizing for you.

[peah-webrtc, 2016/12/21 23:13:50]

Great suggestion! I did not know that!

Done.

+    std::copy(block[i].begin(), block[i].end(), buffer_[i].begin());
+  }
+}
+
+void BlockFramer::InsertBlockAndExtractSubFrame(
+    const std::vector<std::vector<float>>& block,
+    rtc::ArrayView<rtc::ArrayView<float>> sub_frame) {
+  RTC_DCHECK_EQ(num_bands_, block.size());
+  RTC_DCHECK_EQ(num_bands_, sub_frame.size());
+  for (size_t i = 0; i < num_bands_; ++i) {
+    RTC_DCHECK_LE(kSubFrameLength, buffer_[i].size() + kBlockSize);
+    RTC_DCHECK_EQ(kBlockSize, block[i].size());
+    RTC_DCHECK_GE(kBlockSize, buffer_[i].size());
+    RTC_DCHECK_EQ(kSubFrameLength, sub_frame[i].size());
+    const int samples_to_frame = kSubFrameLength - buffer_[i].size();
+    std::copy(buffer_[i].begin(), buffer_[i].end(), sub_frame[i].begin());

[hlundin-webrtc, 2016/12/20 15:10:35]

You can do sub_frame[i].insert(...) here, and skip the DCHECK on the size of
sub_frame[i], if you want to. But that is optional.

[aleloi, 2016/12/21 10:07:45]

sub_frame is ArrayView, not vector. It can only be copied to.

[hlundin-webrtc, 2016/12/21 10:14:19]

Acknowledged. My bad. Ignore those comments when I've slapped them on to
ArrayView objects rather than vectors.

[peah-webrtc, 2016/12/21 23:13:49]

Acknowledged.

[peah-webrtc, 2016/12/21 23:13:50]

Acknowledged.

[peah-webrtc, 2016/12/21 23:13:50]

It seems like arrayview does not allow that. 
Acknowledged.

+    std::copy(block[i].begin(), block[i].begin() + samples_to_frame,

[hlundin-webrtc, 2016/12/20 15:10:34]

Same here; again, optional.

[peah-webrtc, 2016/12/21 23:13:49]

Not allowed by arrayview.

+              sub_frame[i].begin() + buffer_[i].size());
+    buffer_[i].resize(kBlockSize - samples_to_frame);

[hlundin-webrtc, 2016/12/20 15:10:35]

I don't think you have to resize; simply insert().

[peah-webrtc, 2016/12/21 23:13:50]

A resize to 0 was needed before the insert.  But I added the insert.

Done.

+    std::copy(block[i].begin() + samples_to_frame, block[i].end(),
+              buffer_[i].begin());
+  }
+}
+
+}  // namespace webrtc