Add an initial revision of an audio server.

services/media/audio/platform/generic/standard_output_base.cc

Index: services/media/audio/platform/generic/standard_output_base.cc
diff --git a/services/media/audio/platform/generic/standard_output_base.cc b/services/media/audio/platform/generic/standard_output_base.cc
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+++ b/services/media/audio/platform/generic/standard_output_base.cc
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+// Copyright 2015 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 <limits>
+
+#include "base/logging.h"
+#include "services/media/audio/audio_track_impl.h"
+#include "services/media/audio/audio_track_to_output_link.h"
+#include "services/media/audio/platform/generic/mixer.h"
+#include "services/media/audio/platform/generic/standard_output_base.h"
+
+namespace mojo {
+namespace media {
+namespace audio {
+
+static constexpr LocalDuration MAX_TRIM_PERIOD = local_time::from_msec(10);
+constexpr uint32_t StandardOutputBase::MixJob::INVALID_GENERATION;
+
+StandardOutputBase::TrackBookkeeping::TrackBookkeeping() {}
+StandardOutputBase::TrackBookkeeping::~TrackBookkeeping() {}
+
+StandardOutputBase::StandardOutputBase(AudioOutputManager* manager)
+  : AudioOutput(manager) {
+  setup_mix_ =
+    [this] (const AudioTrackImplPtr& track, TrackBookkeeping* info) -> bool {
+      return SetupMix(track, info);
+    };
+
+  process_mix_ =
+    [this] (const AudioTrackImplPtr& track,
+            TrackBookkeeping* info,
+            const AudioPipe::AudioPacketRefPtr& pkt_ref) -> bool {
+      return ProcessMix(track, info, pkt_ref);
+    };
+
+  setup_trim_ =
+    [this] (const AudioTrackImplPtr& track, TrackBookkeeping* info) -> bool {
+      return SetupTrim(track, info);
+    };
+
+  process_trim_ =
+    [this] (const AudioTrackImplPtr& track,
+            TrackBookkeeping* info,
+            const AudioPipe::AudioPacketRefPtr& pkt_ref) -> bool {
+      return ProcessTrim(track, info, pkt_ref);
+    };
+
+  next_sched_time_ = LocalClock::now();
+  next_sched_time_known_ = true;
+}
+
+StandardOutputBase::~StandardOutputBase() {}
+
+void StandardOutputBase::Process() {
+  bool mixed = false;
+  LocalTime now = LocalClock::now();
+
+  // At this point, we should always know when our implementation would like to
+  // be called to do some mixing work next.  If we do not know, then we should
+  // have already shut down.
+  //
+  // If the next sched time has not arrived yet, don't attempt to mix anything.
+  // Just trim the queues and move on.
+  DCHECK(next_sched_time_known_);
+  if (now >= next_sched_time_) {
+    // Clear the flag, if the implementation does not set this flag by calling
+    // SetNextSchedTime during the cycle, we consider it to be an error and shut
+    // down.
+    next_sched_time_known_ = false;
+
+    // As long as our implementation wants to mix more and has not run into a
+    // problem trying to finish the mix job, mix some more.
+    do {
+      ::memset(&cur_mix_job_, 0, sizeof(cur_mix_job_));
+
+      if (!StartMixJob(&cur_mix_job_, now)) {
+        break;
+      }
+
+      ForeachTrack(setup_mix_, process_mix_);
+      mixed = true;
+    } while (FinishMixJob(cur_mix_job_));
+  }
+
+  if (!next_sched_time_known_) {
+    // TODO(johngro): log this as an error.
+    ShutdownSelf();
+    return;
+  }
+
+  // If we mixed nothing this time, make sure that we trim all of our track
+  // queues.  No matter what is going on with the output hardware, we are not
+  // allowed to hold onto the queued data past its presentation time.
+  if (!mixed) {
+    ForeachTrack(setup_trim_, process_trim_);
+  }
+
+  // Figure out when we should wake up to do more work again.  No matter how
+  // long our implementation wants to wait, we need to make sure to wake up and
+  // periodically trim our input queues.
+  LocalTime max_sched_time = now + MAX_TRIM_PERIOD;
+  ScheduleCallback((next_sched_time_ > max_sched_time)
+                   ? max_sched_time
+                   : next_sched_time_);
+}
+
+MediaResult StandardOutputBase::InitializeLink(
+    const AudioTrackToOutputLinkPtr& link) {
+  TrackBookkeeping* bk = AllocBookkeeping();
+  AudioTrackToOutputLink::BookkeepingPtr ref(bk);
+
+  // We should never fail to allocate our bookkeeping.  The only way this can
+  // happen is if we have a badly behaved implementation.
+  if (!bk) { return MediaResult::INTERNAL_ERROR; }
+
+  // We cannot proceed if our track has somehow managed to go away already.
+  AudioTrackImplPtr track = link->GetTrack();
+  if (!track) { return MediaResult::INVALID_ARGUMENT; }
+
+  // Pick a mixer based on the input and output formats.
+  bk->mixer = Mixer::Select(track->Format(), output_format_);
+  if (bk->mixer == nullptr) { return MediaResult::UNSUPPORTED_CONFIG; }
+
+  // Looks like things went well.  Stash a reference to our bookkeeping and get
+  // out.
+  link->output_bookkeeping() = std::move(ref);
+  return MediaResult::OK;
+}
+
+StandardOutputBase::TrackBookkeeping* StandardOutputBase::AllocBookkeeping() {
+  return new TrackBookkeeping();
+}
+
+void StandardOutputBase::ForeachTrack(const TrackSetupTask& setup,
+                                      const TrackProcessTask& process) {
+  for (auto iter = links_.begin(); iter != links_.end(); ) {
+    if (shutting_down()) { return; }
+
+    // Is the track still around?  If so, process it.  Otherwise, remove the
+    // track entry and move on.
+    const AudioTrackToOutputLinkPtr& link = *iter;
+    AudioTrackImplPtr track(link->GetTrack());
+
+    auto tmp_iter = iter++;
+    if (!track) {
+      links_.erase(tmp_iter);
+      continue;
+    }
+
+    // It would be nice to be able to use a dynamic cast for this, but currently
+    // we are building with no-rtti
+    TrackBookkeeping* info =
+      static_cast<TrackBookkeeping*>(link->output_bookkeeping().get());
+    DCHECK(info);
+
+    // Make sure that the mapping between the track's frame time domain and
+    // local time is up to date.
+    info->UpdateTrackTrans(track);
+
+    bool setup_done = false;
+    AudioPipe::AudioPacketRefPtr pkt_ref;
+    while (true) {
+      // Try to grab the front of the packet queue.  If it has been flushed
+      // since the last time we grabbed it, be sure to reset our mixer's
+      // internal filter state.
+      bool was_flushed;
+      pkt_ref = link->LockPendingQueueFront(&was_flushed);
+      if (was_flushed) {
+        info->mixer->Reset();
+      }
+
+      // If the queue is empty, then we are done.
+      if (!pkt_ref) { break; }
+
+      // If we have not set up for this track yet, do so.  If the setup fails
+      // for any reason, stop processing packets for this track.
+      if (!setup_done) {
+        setup_done = setup(track, info);
+        if (!setup_done) { break; }
+      }
+
+      // Now process the packet which is at the front of the track's queue.  If
+      // the packet has been entirely consumed, pop it off the front and proceed
+      // to the next one.  Otherwise, we are finished.
+      if (!process(track, info, pkt_ref)) { break; }
+      link->UnlockPendingQueueFront(&pkt_ref, true);
+    }
+
+    // Unlock the queue and proceed to the next track.
+    link->UnlockPendingQueueFront(&pkt_ref, false);
+
+    // Note: there is no point in doing this for the trim task, but it dosn't
+    // hurt anything, and its easier then introducing another function to the
+    // ForeachTrack arguments to run after each track is processed just for the
+    // purpose of setting this flag.
+    cur_mix_job_.accumulate = true;
+  }
+}
+
+bool StandardOutputBase::SetupMix(const AudioTrackImplPtr& track,
+                                  TrackBookkeeping* info) {
+  // If we need to recompose our transformation from output frame space to input
+  // fractional frames, do so now.
+  DCHECK(info);
+  info->UpdateOutputTrans(cur_mix_job_);
+  cur_mix_job_.frames_produced = 0;
+
+  return true;
+}
+
+bool StandardOutputBase::ProcessMix(
+    const AudioTrackImplPtr& track,
+    TrackBookkeeping* info,
+    const AudioPipe::AudioPacketRefPtr& pkt_ref) {
+  // Sanity check our parameters.
+  DCHECK(info);
+  DCHECK(pkt_ref);
+
+  // We had better have a valid job, or why are we here?
+  DCHECK(cur_mix_job_.buf);
+  DCHECK(cur_mix_job_.buf_frames);
+  DCHECK(cur_mix_job_.frames_produced <= cur_mix_job_.buf_frames);
+
+  // Have we produced all that we are supposed to?  If so, hold the current
+  // packet and move on to the next track.
+  if (cur_mix_job_.frames_produced >= cur_mix_job_.buf_frames) {
+    return false;
+  }
+
+  uint32_t frames_left = cur_mix_job_.buf_frames - cur_mix_job_.frames_produced;
+  void* buf = static_cast<uint8_t*>(cur_mix_job_.buf)
+            + (cur_mix_job_.frames_produced * output_bytes_per_frame_);
+
+  // Figure out where this job starts, expressed in fractional input frames.
+  int64_t start_pts_ftf;
+  bool good = info->out_frames_to_track_frames.DoForwardTransform(
+      cur_mix_job_.start_pts_of + cur_mix_job_.frames_produced,
+      &start_pts_ftf);
+  DCHECK(good);
+
+  // If the start of this mix job is past the end of this packet presentation,
+  // do no mixing.  Let the ForeachTrack loop know that we are done with the
+  // packet and it can be released.
+  if (start_pts_ftf >= pkt_ref->end_pts()) {
+    return true;
+  }
+
+  // If this track is currently paused (or being sampled extremely slowly), our
+  // step size will be zero.  We know that this packet will be relevant at some
+  // point in the future, but right now it contributes nothing.  Tell the
+  // ForeachTrack loop that we are done and to hold onto this packet for now.
+  if (!info->step_size) {
+    return false;
+  }
+
+  // Figure out how many output samples into the current job this packet starts.
+  int64_t delta;
+  int64_t output_offset_64;
+  if (pkt_ref->start_pts() > start_pts_ftf) {
+    delta             = pkt_ref->start_pts() - start_pts_ftf;
+    output_offset_64  = delta + info->step_size - 1;
+    output_offset_64 /= info->step_size;
+  } else {
+    output_offset_64 = 0;
+  }
+  DCHECK_GE(output_offset_64, 0);
+
+  // If this packet starts after the end of this job (entirely in the future),
+  // then we are done for now.
+  if (output_offset_64 >= frames_left) {
+    return false;
+  }
+
+  // Figure out the offset (in fractional frames) into this packet where we want
+  // to start sampling.
+  int64_t  input_offset_64;
+  if (output_offset_64) {
+    input_offset_64  = output_offset_64 * info->step_size;
+    input_offset_64 -= delta;
+    DCHECK_LT(input_offset_64, info->step_size);
+  } else {
+    input_offset_64 = start_pts_ftf - pkt_ref->start_pts();
+  }
+  DCHECK_GE(input_offset_64, 0);
+  DCHECK_LE(input_offset_64, std::numeric_limits<int32_t>::max());
+  DCHECK_LT(input_offset_64, pkt_ref->end_pts() - pkt_ref->start_pts());
+
+  uint32_t input_offset  = static_cast<uint32_t>(input_offset_64);
+  uint32_t output_offset = static_cast<uint32_t>(output_offset_64);
+  const auto& regions = pkt_ref->regions();
+  DCHECK(info->mixer != nullptr);
+
+  for (size_t i = 0;
+      (i < regions.size()) && (output_offset < frames_left);
+      ++i) {
+    const auto& region = regions[i];
+
+    if (input_offset >= region.frac_frame_len) {
+      input_offset -= region.frac_frame_len;
+      continue;
+    }
+
+    bool consumed_source = info->mixer->Mix(buf,
+                                            frames_left,
+                                            &output_offset,
+                                            region.base,
+                                            region.frac_frame_len,
+                                            &input_offset,
+                                            info->step_size,
+                                            cur_mix_job_.accumulate);
+    DCHECK_LE(output_offset, frames_left);
+
+    if (!consumed_source) {
+      // Looks like we didn't consume all of this region.  Assert that we have
+      // produced all of our frames and we are done.
+      DCHECK(output_offset == frames_left);
+      return false;
+    }
+
+    input_offset -= region.frac_frame_len;
+  }
+
+  cur_mix_job_.frames_produced += output_offset;
+  DCHECK(cur_mix_job_.frames_produced <= cur_mix_job_.buf_frames);
+  return true;
+}
+
+bool StandardOutputBase::SetupTrim(const AudioTrackImplPtr& track,
+                                   TrackBookkeeping* info) {
+  // Compute the cutoff time we will use to decide wether or not to trim
+  // packets.  ForeachTracks has already updated our transformation, no need
+  // for us to do so here.
+  DCHECK(info);
+
+  int64_t local_now_ticks = LocalClock::now().time_since_epoch().count();
+
+  // The behavior of the RateControlBase implementation guarantees that the
+  // transformation into the media timeline is never singular.  If the
+  // forward transformation fails it can only be because of an overflow,
+  // which should be impossible unless the user has defined a playback rate
+  // where the ratio between media time ticks and local time ticks is
+  // greater than one.
+  //
+  // IOW - this should never happen.  If it does, we just stop processing
+  // payloads.
+  //
+  // TODO(johngro): Log an error?  Communicate this to the user somehow?
+  if (!info->lt_to_track_frames.DoForwardTransform(local_now_ticks,
+                                                  &trim_threshold_)) {
+    return false;
+  }
+
+  return true;
+}
+
+bool StandardOutputBase::ProcessTrim(
+    const AudioTrackImplPtr& track,
+    TrackBookkeeping* info,
+    const AudioPipe::AudioPacketRefPtr& pkt_ref) {
+  DCHECK(pkt_ref);
+
+  // If the presentation end of this packet is in the future, stop trimming.
+  if (pkt_ref->end_pts() > trim_threshold_) {
+    return false;
+  }
+
+  return true;
+}
+
+void StandardOutputBase::TrackBookkeeping::UpdateTrackTrans(
+    const AudioTrackImplPtr& track) {
+  LinearTransform tmp;
+  uint32_t gen;
+
+  DCHECK(track);
+  track->SnapshotRateTrans(&tmp, &gen);
+
+  // If the local time -> media time transformation has not changed since the
+  // last time we examines it, just get out now.
+  if (lt_to_track_frames_gen == gen) { return; }
+
+  // The transformation has changed, re-compute the local time -> track frame
+  // transformation.
+  LinearTransform scale(0, track->FractionalFrameToMediaTimeRatio(), 0);
+  bool good;
+
+  lt_to_track_frames.a_zero = tmp.a_zero;
+  good = scale.DoReverseTransform(tmp.b_zero, &lt_to_track_frames.b_zero);
+  DCHECK(good);
+  good = LinearTransform::Ratio::Compose(scale.scale,
+                                         tmp.scale,
+                                         &lt_to_track_frames.scale);
+  DCHECK(good);
+
+  // Update the generation, and invalidate the output to track generation.
+  lt_to_track_frames_gen = gen;
+  out_frames_to_track_frames_gen = MixJob::INVALID_GENERATION;
+}
+
+void StandardOutputBase::TrackBookkeeping::UpdateOutputTrans(
+    const MixJob& job) {
+  // We should not be here unless we have a valid mix job.  From our point of
+  // view, this means that we have a job which supplies a valid transformation
+  // from local time to output frames.
+  DCHECK(job.local_to_output);
+  DCHECK(job.local_to_output_gen != MixJob::INVALID_GENERATION);
+
+  // If our generations match, we don't need to re-compute anything.  Just use
+  // what we have already.
+  if (out_frames_to_track_frames_gen == job.local_to_output_gen) { return; }
+
+  // Assert that we have a good mapping from local time to fractional track
+  // frames.
+  //
+  // TODO(johngro): Don't assume that 0 means invalid.  Make it a proper
+  // constant defined somewhere.
+  DCHECK(lt_to_track_frames_gen);
+
+  // Compose the job supplied transformation from local to output with the
+  // track supplied mapping from local to fraction input frames to produce a
+  // transformation which maps from output frames to fractional input frames.
+  //
+  // TODO(johngro): Make this composition operation part of the LinearTransform
+  // class instead of doing it by hand here.  Its a more complicated task that
+  // one might initially think, because of the need to deal with the
+  // intermediate offset term, and distributing it to either side of the end of
+  // the transformation with a minimum amt of loss, while avoiding overflow.
+  //
+  // For now, we punt, do it by hand and just assume that everything went well.
+  LinearTransform& dst = out_frames_to_track_frames;
+
+  // Distribute the intermediate offset entirely to the fractional frame domain
+  // for now.  We can do better by extracting portions of the intermedate
+  // offset that can be scaled by the ratios on either side of with without
+  // loss, but for now this should be close enough.
+  int64_t intermediate = job.local_to_output->a_zero
+                       - lt_to_track_frames.a_zero;
+  int64_t track_frame_offset;
+
+  // TODO(johngro): add routines to LinearTransform::Ratio which allow us to
+  // scale using just a ratio without needing to create a linear transform with
+  // empty offsets.
+  LinearTransform tmp(0, lt_to_track_frames.scale, 0);
+  bool good = tmp.DoForwardTransform(intermediate, &track_frame_offset);
+  DCHECK(good);
+
+  dst.a_zero = job.local_to_output->b_zero;
+  dst.b_zero = lt_to_track_frames.b_zero + track_frame_offset;
+
+  // TODO(johngro): Add options to allow us to invert one or both of the ratios
+  // during composition instead of needing to make a temporary ratio to
+  // acomplish the task.
+  LinearTransform::Ratio tmp_ratio(job.local_to_output->scale.denominator,
+                                   job.local_to_output->scale.numerator);
+  good = LinearTransform::Ratio::Compose(tmp_ratio,
+                                         lt_to_track_frames.scale,
+                                         &dst.scale);;
+  DCHECK(good);
+
+  // Finally, compute the step size in fractional frames.  IOW, every time we
+  // move forward one output frame, how many fractional frames of input do we
+  // consume.  Don't bother doing the multiplication if we already know that the
+  // numerator is zero.
+  //
+  // TODO(johngro): same complaint as before... Do this without a temp.  The
+  // special casing should be handled in the routine added to
+  // LinearTransform::Ratio.
+  DCHECK(dst.scale.denominator);
+  if (!dst.scale.numerator) {
+    step_size = 0;
+  } else {
+    LinearTransform tmp(0, dst.scale, 0);
+    int64_t tmp_step_size;
+
+    good = tmp.DoForwardTransform(1, &tmp_step_size);
+
+    DCHECK(good);
+    DCHECK_GE(tmp_step_size, 0);
+    DCHECK_LE(tmp_step_size, std::numeric_limits<uint32_t>::max());
+
+    step_size = static_cast<uint32_t>(tmp_step_size);
+  }
+
+  // Done, update our generation.
+  out_frames_to_track_frames_gen = job.local_to_output_gen;
+}
+
+}  // namespace audio
+}  // namespace media
+}  // namespace mojo