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 "AudioStream.h"
  11 #include "nsTArray.h"
  12 #include "mozilla/LinkedList.h"
  13 #include "mozilla/NotNull.h"
  14 #include "mozilla/PodOperations.h"
  15
  16 namespace mozilla {
  17
  18 struct MixerCallbackReceiver {
  19   virtual void MixerCallback(AudioDataValue* aMixedBuffer,
  20                              AudioSampleFormat aFormat, uint32_t aChannels,
  21                              uint32_t aFrames, uint32_t aSampleRate) = 0;
  22 };
  23 /**
  24  * This class mixes multiple streams of audio together to output a single audio
  25  * stream.
  26  *
  27  * AudioMixer::Mix is to be called repeatedly with buffers that have the same
  28  * length, sample rate, sample format and channel count. This class works with
  29  * interleaved and plannar buffers, but the buffer mixed must be of the same
  30  * type during a mixing cycle.
  31  *
  32  * When all the tracks have been mixed, calling FinishMixing will call back with
  33  * a buffer containing the mixed audio data.
  34  *
  35  * This class is not thread safe.
  36  */
  37 class AudioMixer {
  38  public:
  39   AudioMixer() : mFrames(0), mChannels(0), mSampleRate(0) {}
  40
  41   ~AudioMixer() {
  42     MixerCallback* cb;
  43     while ((cb = mCallbacks.popFirst())) {
  44       delete cb;
  45     }
  46   }
  47
  48   void StartMixing() { mSampleRate = mChannels = mFrames = 0; }
  49
  50   /* Get the data from the mixer. This is supposed to be called when all the
  51    * tracks have been mixed in. The caller should not hold onto the data. */
  52   void FinishMixing() {
  53     MOZ_ASSERT(mChannels && mSampleRate, "Mix not called for this cycle?");
  54     for (MixerCallback* cb = mCallbacks.getFirst(); cb != nullptr;
  55          cb = cb->getNext()) {
  56       MixerCallbackReceiver* receiver = cb->mReceiver;
  57       MOZ_ASSERT(receiver);
  58       receiver->MixerCallback(mMixedAudio.Elements(),
  59                               AudioSampleTypeToFormat<AudioDataValue>::Format,
  60                               mChannels, mFrames, mSampleRate);
  61     }
  62     PodZero(mMixedAudio.Elements(), mMixedAudio.Length());
  63     mSampleRate = mChannels = mFrames = 0;
  64   }
  65
  66   /* Add a buffer to the mix. The buffer can be null if there's nothing to mix
  67    * but the callback is still needed. */
  68   void Mix(AudioDataValue* aSamples, uint32_t aChannels, uint32_t aFrames,
  69            uint32_t aSampleRate) {
  70     if (!mFrames && !mChannels) {
  71       mFrames = aFrames;
  72       mChannels = aChannels;
  73       mSampleRate = aSampleRate;
  74       EnsureCapacityAndSilence();
  75     }
  76
  77     MOZ_ASSERT(aFrames == mFrames);
  78     MOZ_ASSERT(aChannels == mChannels);
  79     MOZ_ASSERT(aSampleRate == mSampleRate);
  80
  81     if (!aSamples) {
  82       return;
  83     }
  84
  85     for (uint32_t i = 0; i < aFrames * aChannels; i++) {
  86       mMixedAudio[i] += aSamples[i];
  87     }
  88   }
  89
  90   void AddCallback(NotNull<MixerCallbackReceiver*> aReceiver) {
  91     mCallbacks.insertBack(new MixerCallback(aReceiver));
  92   }
  93
  94   bool FindCallback(MixerCallbackReceiver* aReceiver) {
  95     for (MixerCallback* cb = mCallbacks.getFirst(); cb != nullptr;
  96          cb = cb->getNext()) {
  97       if (cb->mReceiver == aReceiver) {
  98         return true;
  99       }
 100     }
 101     return false;
 102   }
 103
 104   bool RemoveCallback(MixerCallbackReceiver* aReceiver) {
 105     for (MixerCallback* cb = mCallbacks.getFirst(); cb != nullptr;
 106          cb = cb->getNext()) {
 107       if (cb->mReceiver == aReceiver) {
 108         cb->remove();
 109         delete cb;
 110         return true;
 111       }
 112     }
 113     return false;
 114   }
 115
 116  private:
 117   void EnsureCapacityAndSilence() {
 118     if (mFrames * mChannels > mMixedAudio.Length()) {
 119       mMixedAudio.SetLength(mFrames * mChannels);
 120     }
 121     PodZero(mMixedAudio.Elements(), mMixedAudio.Length());
 122   }
 123
 124   class MixerCallback : public LinkedListElement<MixerCallback> {
 125    public:
 126     explicit MixerCallback(NotNull<MixerCallbackReceiver*> aReceiver)
 127         : mReceiver(aReceiver) {}
 128     NotNull<MixerCallbackReceiver*> mReceiver;
 129   };
 130
 131   /* Function that is called when the mixing is done. */
 132   LinkedList<MixerCallback> mCallbacks;
 133   /* Number of frames for this mixing block. */
 134   uint32_t mFrames;
 135   /* Number of channels for this mixing block. */
 136   uint32_t mChannels;
 137   /* Sample rate the of the mixed data. */
 138   uint32_t mSampleRate;
 139   /* Buffer containing the mixed audio data. */
 140   nsTArray<AudioDataValue> mMixedAudio;
 141 };
 142
 143 }  // namespace mozilla
 144
 145 #endif  // MOZILLA_AUDIOMIXER_H_