dom/media/AudioMixer.h

   1 /* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
   2 /* This Source Code Form is subject to the terms of the Mozilla Public
   3  * License, v. 2.0. If a copy of the MPL was not distributed with this file,
   4  * You can obtain one at http://mozilla.org/MPL/2.0/. */
   5
   6 #ifndef MOZILLA_AUDIOMIXER_H_
   7 #define MOZILLA_AUDIOMIXER_H_
   8
   9 #include "AudioSampleFormat.h"
  10 #include "AudioSegment.h"
  11 #include "AudioStream.h"
  12 #include "nsTArray.h"
  13 #include "mozilla/NotNull.h"
  14 #include "mozilla/PodOperations.h"
  15
  16 namespace mozilla {
  17
  18 struct MixerCallbackReceiver {
  19   // MixerCallback MAY modify aMixedBuffer but MUST clear
  20   // aMixedBuffer->mBuffer if its data is to live longer than the duration of
  21   // the callback.
  22   virtual void MixerCallback(AudioChunk* aMixedBuffer,
  23                              uint32_t aSampleRate) = 0;
  24 };
  25 /**
  26  * This class mixes multiple streams of audio together to output a single audio
  27  * stream.
  28  *
  29  * AudioMixer::Mix is to be called repeatedly with buffers that have the same
  30  * length, sample rate, sample format and channel count. This class works with
  31  * planar buffers.
  32  *
  33  * When all the tracks have been mixed, calling MixedChunk() will provide
  34  * a buffer containing the mixed audio data.
  35  *
  36  * This class is not thread safe.
  37  */
  38 class AudioMixer {
  39  public:
  40   AudioMixer() { mChunk.mBufferFormat = AUDIO_OUTPUT_FORMAT; }
  41
  42   ~AudioMixer() = default;
  43
  44   void StartMixing() {
  45     mChunk.mDuration = 0;
  46     mSampleRate = 0;
  47   }
  48
  49   /* Get the data from the mixer. This is supposed to be called when all the
  50    * tracks have been mixed in. The caller MAY modify the chunk but MUST clear
  51    * mBuffer if its data needs to survive the next call to Mix(). */
  52   AudioChunk* MixedChunk() {
  53     MOZ_ASSERT(mSampleRate, "Mix not called for this cycle?");
  54     mSampleRate = 0;
  55     return &mChunk;
  56   };
  57
  58   /* Add a buffer to the mix. The buffer can be null if there's nothing to mix
  59    * but the callback is still needed. */
  60   void Mix(AudioDataValue* aSamples, uint32_t aChannels, uint32_t aFrames,
  61            uint32_t aSampleRate) {
  62     if (!mChunk.mDuration) {
  63       mChunk.mDuration = aFrames;
  64       MOZ_ASSERT(aChannels > 0);
  65       mChunk.mChannelData.SetLength(aChannels);
  66       mSampleRate = aSampleRate;
  67       EnsureCapacityAndSilence();
  68     }
  69
  70     MOZ_ASSERT(aFrames == mChunk.mDuration);
  71     MOZ_ASSERT(aChannels == mChunk.ChannelCount());
  72     MOZ_ASSERT(aSampleRate == mSampleRate);
  73
  74     if (!aSamples) {
  75       return;
  76     }
  77
  78     for (uint32_t i = 0; i < aFrames * aChannels; i++) {
  79       mChunk.ChannelDataForWrite<AudioDataValue>(0)[i] += aSamples[i];
  80     }
  81   }
  82
  83  private:
  84   void EnsureCapacityAndSilence() {
  85     uint32_t sampleCount = mChunk.mDuration * mChunk.ChannelCount();
  86     if (!mChunk.mBuffer || sampleCount > mSampleCapacity) {
  87       CheckedInt<size_t> bufferSize(sizeof(AudioDataValue));
  88       bufferSize *= sampleCount;
  89       mChunk.mBuffer = SharedBuffer::Create(bufferSize);
  90       mSampleCapacity = sampleCount;
  91     }
  92     MOZ_ASSERT(!mChunk.mBuffer->IsShared());
  93     mChunk.mChannelData[0] =
  94         static_cast<SharedBuffer*>(mChunk.mBuffer.get())->Data();
  95     for (size_t i = 1; i < mChunk.ChannelCount(); ++i) {
  96       mChunk.mChannelData[i] =
  97           mChunk.ChannelData<AudioDataValue>()[0] + i * mChunk.mDuration;
  98     }
  99     PodZero(mChunk.ChannelDataForWrite<AudioDataValue>(0), sampleCount);
 100   }
 101
 102   /* Buffer containing the mixed audio data. */
 103   AudioChunk mChunk;
 104   /* Size allocated for mChunk.mBuffer. */
 105   uint32_t mSampleCapacity = 0;
 106   /* Sample rate the of the mixed data. */
 107   uint32_t mSampleRate = 0;
 108 };
 109
 110 }  // namespace mozilla
 111
 112 #endif  // MOZILLA_AUDIOMIXER_H_