[Chromecast] Process streams with different post-processing.

chromecast/media/cma/backend/alsa/filter_group.h

Index: chromecast/media/cma/backend/alsa/filter_group.h
diff --git a/chromecast/media/cma/backend/alsa/filter_group.h b/chromecast/media/cma/backend/alsa/filter_group.h
new file mode 100644
index 0000000000000000000000000000000000000000..7b059e5a2b11c9d2f7ed3eac45d181ad95470c17
--- /dev/null
+++ b/chromecast/media/cma/backend/alsa/filter_group.h
@@ -0,0 +1,81 @@
+// Copyright 2017 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.
+
+#ifndef CHROMECAST_MEDIA_CMA_BACKEND_ALSA_FILTER_GROUP_H_
+#define CHROMECAST_MEDIA_CMA_BACKEND_ALSA_FILTER_GROUP_H_
+

[kmackay, 2017/02/23 20:52:56]

<memory>
<vector>
<stdint.h>

[bshaya, 2017/02/24 00:17:07]

Done.

+#include <string>
+#include <unordered_set>
+
+#include "chromecast/media/cma/backend/alsa/audio_filter_factory.h"
+#include "chromecast/media/cma/backend/alsa/stream_mixer_alsa.h"
+
+namespace chromecast {
+namespace media {
+class AudioBus;
+
+// FilterGroup contains state for an AudioFilter.
+// It takes multiple StreamMixerAlsa::InputQueues,
+// mixes them, and processes them.
+
+// ActiveInputs are added with TryAddActiveInput(), then cleared when
+// MixAndFilter() is called (they must be added each time data is queried).
+class FilterGroup {
+ public:
+  // |input_types| is a set of strings that is used as a filter to determine
+  // if an input belongs to this group (InputQueue->name() must exactly match an
+  // entry in |input_types| to be processed by this group.
+  // |filter_type| is passed to AudioFilterFactory to create an AudioFilter.

[kmackay, 2017/02/23 20:52:56]

I guess technically we could determine which filter group an input belongs to
when the input is created (since the device id isn't going to change). So we
could store a pointer to the filter group in the StreamMixerAlsaInputImpl
itself, and then when adding active inputs, just add it to the stored filter
group rather than iterating through all the groups.

[bshaya, 2017/02/24 00:17:07]

Done.

+  FilterGroup(const std::unordered_set<std::string>& input_types,
+              AudioFilterFactory::FilterType filter_type);
+
+  // Sets the sample rate and format in the AudioFilter.
+  void Initialize(int output_samples_per_second, ::media::SampleFormat format);
+
+  // Adds |input| to |active_inputs_| if |input->name()| matches
+  // an entry in |input_types_|.
+  // If |true| is returned, the caller should get the processed data with
+  // GetInterleaved.
+  // If |false| is returned, there is no new data, and the data from
+  // GetInterleaved may be stale.
+  bool TryAddActiveInput(StreamMixerAlsa::InputQueue* input);
+
+  // Retrieves a pointer to the output buffer |interleaved_|.
+  std::vector<uint8_t>* GetInterleaved();
+
+  // Mixes all active inputs and passes them through the audio filter.
+  // |active_inputs_| is cleared afterwards.
+  bool MixAndFilter(int chunk_size);
+
+  // Overwrites |interleaved_| with 0's, ensuring at least
+  // |chunk_size| bytes.
+  void ClearInterleaved(int chunk_size);
+
+ private:
+  void ResizeBuffersIfNecessary(int chunk_size);
+  int BytesPerOutputFormatSample();
+
+  const std::unordered_set<std::string> input_types_;
+  std::vector<StreamMixerAlsa::InputQueue*> active_inputs_;
+
+  int output_samples_per_second_;
+  ::media::SampleFormat sample_format_;
+
+  // Buffers that hold audio data while it is mixed.
+  // These are kept as members of this class to minimize copies and
+  // allocations.
+  std::unique_ptr<::media::AudioBus> temp_;
+  std::unique_ptr<::media::AudioBus> mixed_;
+  std::vector<uint8_t> interleaved_;
+
+  std::unique_ptr<AudioFilterInterface> audio_filter_;
+  int silence_frames_filtered_;
+
+  FilterGroup(const FilterGroup&) = delete;
+  const FilterGroup& operator=(const FilterGroup&) = delete;

[kmackay, 2017/02/23 20:52:56]

DISALLOW_COPY_AND_ASSIGN is still preferred (?) Or did they change the style
guide?

[bshaya, 2017/02/24 00:17:07]

The Google Style Guide only mentions = delete.
The Chromium Style Guide is silent on the matter.

[halliwell, 2017/02/24 00:28:09]

Search the chromium-dev mailing list, there was a discussion there.

+};
+
+}  // namespace media
+}  // namespace chromecast
+#endif  // CHROMECAST_MEDIA_CMA_BACKEND_ALSA_FILTER_GROUP_H_