Motown in-proc streaming framework used to implement media services.

services/media/framework/conversion_pipeline_builder.cc

+// Copyright 2016 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 "services/media/framework/conversion_pipeline_builder.h"
+#include "services/media/framework/ostream.h"
+#include "services/media/framework/parts/decoder.h"
+#include "services/media/framework/parts/lpcm_reformatter.h"
+
+namespace mojo {
+namespace media {
+
+namespace {
+
+enum class AddResult {
+  kFailed, // Can't convert.
+  kProgressed, // Added a conversion transform.
+  kFinished // Done adding conversion transforms.
+};
+
+// Produces a score for in_type with respect to out_type_set. The score
+// is used to compare type sets to see which represents the best goal for
+// conversion. Higher scores are preferred. A score of zero indicates that
+// in_type is incompatible with out_type_set.
+int Score(
+    const LpcmStreamType& in_type,
+    const LpcmStreamTypeSet& out_type_set) {
+  // TODO(dalesat): Plenty of room for more subtlety here. Maybe actually
+  // measure conversion costs (cpu, quality, etc) and reflect them here.
+
+  int score = 1; // We can convert anything, so 1 is the minimum score.
+
+  if (in_type.sample_format() == out_type_set.sample_format() ||
+      out_type_set.sample_format() == LpcmStreamType::SampleFormat::kAny) {
+    // Prefer not to convert sample format.
+    score += 10;
+  } else {
+    // Prefer higher-quality formats.
+    switch (out_type_set.sample_format()) {
+      case LpcmStreamType::SampleFormat::kUnsigned8:
+        break;
+      case LpcmStreamType::SampleFormat::kSigned16:
+        score += 1;
+        break;
+      case LpcmStreamType::SampleFormat::kSigned24In32:
+        score += 2;
+        break;
+      case LpcmStreamType::SampleFormat::kFloat:
+        score += 3;
+        break;
+      default:
+        NOTREACHED() << "unsupported sample format "
+            << out_type_set.sample_format();
+    }
+  }
+
+  if (out_type_set.channels().contains(in_type.channels())) {
+    // Prefer not to mixdown/up.
+    score += 10;
+  } else {
+    return 0; // TODO(dalesat): Remove when we have mixdown/up.
+  }
+
+  if (out_type_set.frames_per_second().
+      contains(in_type.frames_per_second())) {
+    // Very much prefer not to resample.
+    score += 50;
+  } else {
+    return 0; // TODO(dalesat): Remove when we have resamplers.
+  }
+
+  return score;
+}
+
+// Finds the media type set that best matches in_type.
+const StreamTypeSetPtr* FindBestLpcm(
+    const LpcmStreamType& in_type,
+    const StreamTypeSetsPtr& out_type_sets) {
+  const StreamTypeSetPtr* best = nullptr;
+  int best_score = 0;
+  // Array has no const iterator, hence the for(;;).
+  for (size_t i = 0; i < out_type_sets->size(); i++) {
+    const StreamTypeSetPtr& out_type_set = (*out_type_sets)[i];
+    switch (out_type_set->scheme()) {
+      case StreamType::Scheme::kAnyElementary:
+      case StreamType::Scheme::kAnyAudio:
+      case StreamType::Scheme::kAny:
+        // Wildcard scheme allows any type without conversion.
+        return &out_type_set;
+      case StreamType::Scheme::kLpcm: {
+        int score = Score(in_type, *out_type_set->lpcm());
+        if (best_score < score) {
+          best_score = score;
+          best = &out_type_set;
+        }
+        break;
+      }
+      default:
+        break;
+    }
+  }
+  return best;
+}
+
+// Attempts to add transforms to the pipeline given an input compressed audio
+// stream type with (in_type) and the set of output types we need to convert to
+// (out_type_sets). If the call succeeds, *out_type is set to the new output
+// type. Otherwise, *out_type is set to nullptr.
+AddResult AddTransformsForCompressedAudio(
+    const CompressedAudioStreamType& in_type,
+    const StreamTypePtr& in_type_ptr,
+    const StreamTypeSetsPtr& out_type_sets,
+    Engine& engine,
+    Engine::Output* output,
+    StreamTypePtr* out_type) {
+  DCHECK(out_type);
+
+  // See if we have a matching COMPRESSED_AUDIO type.
+  // Array has no const iterator, hence the for(;;).
+  for (size_t i = 0; i < out_type_sets->size(); i++) {
+    const StreamTypeSetPtr& out_type_set = (*out_type_sets)[i];
+    switch (out_type_set->scheme()) {
+      case StreamType::Scheme::kAnyElementary:
+      case StreamType::Scheme::kAnyAudio:
+      case StreamType::Scheme::kAny:
+        // Wildcard scheme allows any type without conversion.
+        *out_type = in_type.Clone();
+        return AddResult::kFinished;
+      case StreamType::Scheme::kCompressedAudio: {
+        if (out_type_set->compressed_audio()->contains(in_type)) {
+          // No transform needed.
+          *out_type = in_type.Clone();
+          return AddResult::kFinished;
+        }
+        break;
+      }
+      default:
+        break;
+    }
+    // TODO(dalesat): Support a different compressed output type by transcoding.
+  }
+
+  // Find the best LPCM output type.
+  const StreamTypeSetPtr* best = FindBestLpcm(in_type, out_type_sets);
+  if (best == nullptr) {
+    // No candidates found.
+    *out_type = nullptr;
+    return AddResult::kFailed;
+  }
+
+  DCHECK_EQ((*best)->scheme(), StreamType::Scheme::kLpcm);
+
+  // Need to decode. Create a decoder and go from there.
+  DecoderPtr decoder;
+  Result result = Decoder::Create(in_type_ptr, &decoder);
+  if (result !=  Result::kOk) {
+    // No decoder found.
+    *out_type = nullptr;
+    return AddResult::kFailed;
+  }
+
+  *output = engine.Connect(*output, engine.Add(decoder)).output();
+  *out_type = decoder->output_stream_type();
+
+  return AddResult::kProgressed;
+}
+
+// Attempts to add transforms to the pipeline given an input LPCM stream type
+// (in_type) and the output lpcm stream type set for the type we need to convert
+// to (out_type_set). If the call succeeds, *out_type is set to the new output
+// type. Otherwise, *out_type is set to nullptr.
+AddResult AddTransformsForLpcm(
+    const LpcmStreamType& in_type,
+    const LpcmStreamTypeSet& out_type_set,
+    Engine& engine,
+    Engine::Output* output,
+    StreamTypePtr* out_type) {
+  DCHECK(out_type);
+
+  // TODO(dalesat): Room for more intelligence here wrt transform ordering and
+  // transforms that handle more than one conversion.
+  if (in_type.sample_format() != out_type_set.sample_format() &&
+      out_type_set.sample_format() != LpcmStreamType::SampleFormat::kAny) {
+    // The reformatter will fix interleave conversion.
+    *output = engine.Connect(
+        *output,
+        engine.Add(LpcmReformatter::New(in_type, out_type_set))).output();
+  }
+
+  if (!out_type_set.channels().contains(in_type.channels())) {
+    // TODO(dalesat): Insert mixdown/up transform.
+    NOTREACHED() << "conversion requires mixdown/up - not supported";

[johngro, 2016/01/20 00:25:32]

why not just LOG(ERROR) or MOJO_LOG(ERROR) instead of NOTREACHED?  is it that
the not reached form ASSERTs in the process?

[dalesat, 2016/01/25 17:47:29]

The NOTREACHED will be removed as part of addressing the TODO. In the mean time,
I want the code to fail noisily if I try to make it do things that aren't
implemented.

[johngro, 2016/01/27 22:35:22]

Understood, but not really what I was asking.  I wanted to know what the
behavior of the macro was, and did it assert/dcheck.

I researched the answer to my own question; NOTREACHED is defined in base
logging.  In a non-chromeOS build, it evaluates to DCHECK(false).  DCHECK(false)
(in addition to dchecking) provides a lazy logstream at level DCHECK to eat the
ostream parameters.

On chromeOS, a special function (LogErrorNotReached) is called, and the ostream
parameters are always discarded.

TL;DR? Ack

[dalesat, 2016/01/28 18:49:15]

Acknowledged.

+    *out_type = nullptr;
+    return AddResult::kFailed;
+  }
+
+  if (!out_type_set.frames_per_second().contains(in_type.frames_per_second())) {
+    // TODO(dalesat): Insert resampler.
+    NOTREACHED() << "conversion requires resampling - not supported";
+    *out_type = nullptr;
+    return AddResult::kFailed;
+  }
+
+  // Build the resulting media type.
+  *out_type = LpcmStreamType::New(
+      out_type_set.sample_format() == LpcmStreamType::SampleFormat::kAny ?
+          in_type.sample_format() :
+          out_type_set.sample_format(),
+      in_type.channels(),
+      in_type.frames_per_second());
+
+  return AddResult::kFinished;
+}
+
+// Attempts to add transforms to the pipeline given an input media type with
+// scheme LPCM (in_type) and the set of output types we need to convert to
+// (out_type_sets). If the call succeeds, *out_type is set to the new output
+// type. Otherwise, *out_type is set to nullptr.
+AddResult AddTransformsForLpcm(
+    const LpcmStreamType& in_type,
+    const StreamTypeSetsPtr& out_type_sets,
+    Engine& engine,
+    Engine::Output* output,
+    StreamTypePtr* out_type) {
+  DCHECK(out_type);
+
+  const StreamTypeSetPtr* best = FindBestLpcm(in_type, out_type_sets);
+  if (best == nullptr) {
+    // TODO(dalesat): Support a compressed output type by encoding.
+    NOTREACHED() << "conversion using encoder not supported";
+    *out_type = nullptr;
+    return AddResult::kFailed;
+  }
+
+  switch ((*best)->scheme()) {
+    case StreamType::Scheme::kAnyElementary:
+    case StreamType::Scheme::kAnyAudio:
+    case StreamType::Scheme::kAny:
+      // Wildcard scheme allows any type without conversion.
+      *out_type = in_type.Clone();
+      return AddResult::kFinished;
+    case StreamType::Scheme::kLpcm:
+      return AddTransformsForLpcm(
+          in_type,
+          *(*best)->lpcm(),
+          engine,
+          output,
+          out_type);
+    default:
+      NOTREACHED() << "FindBestLpcm produced unexpected type set scheme"
+          << (*best)->scheme();
+      return AddResult::kFailed;
+  }
+}
+
+// Attempts to add transforms to the pipeline given an input media type of any
+// scheme (in_type) and the set of output types we need to convert to
+// (out_type_sets). If the call succeeds, *out_type is set to the new output
+// type. Otherwise, *out_type is set to nullptr.
+AddResult AddTransforms(
+    const StreamTypePtr& in_type,
+    const StreamTypeSetsPtr& out_type_sets,
+    Engine& engine,
+    Engine::Output* output,
+    StreamTypePtr* out_type) {
+  DCHECK(in_type);
+  DCHECK(out_type);
+
+  switch (in_type->scheme()) {
+    case StreamType::Scheme::kLpcm:
+      return AddTransformsForLpcm(
+          *in_type->lpcm(),
+          out_type_sets,
+          engine,
+          output,
+          out_type);
+    case StreamType::Scheme::kCompressedAudio:
+      return AddTransformsForCompressedAudio(
+          *in_type->compressed_audio(),
+          in_type,
+          out_type_sets,
+          engine,
+          output,
+          out_type);
+    default:
+      NOTREACHED() << "conversion not supported for scheme"
+          << in_type->scheme();
+      *out_type = nullptr;
+      return AddResult::kFailed;
+  }
+}
+
+}  // namespace
+
+bool BuildConversionPipeline(
+    const StreamTypePtr& in_type,
+    const StreamTypeSetsPtr& out_type_sets,
+    Engine& engine,
+    Engine::Output* output,
+    StreamTypePtr* out_type) {
+  DCHECK(in_type);
+  DCHECK(out_type_sets);
+  DCHECK(output);
+  DCHECK(out_type);
+
+  Engine::Output out = *output;
+
+  const StreamTypePtr* type_to_convert = &in_type;
+  StreamTypePtr next_in_type;
+  while (true) {
+    StreamTypePtr converted_type;
+    switch (AddTransforms(
+        *type_to_convert,
+        out_type_sets,
+        engine,
+        &out,
+        &converted_type)) {
+      case AddResult::kFailed:
+        // Failed to find a suitable conversion. Return the pipeline to its
+        // original state.
+        engine.RemoveAll(*output);
+        *out_type = nullptr;
+        return false;
+      case AddResult::kProgressed:
+        // Made progress. Continue.
+        break;
+      case AddResult::kFinished:
+        // No further conversion required.
+        *output = out;
+        *out_type = std::move(converted_type);
+        return true;
+    }
+
+    next_in_type = std::move(converted_type);
+    type_to_convert = &next_in_type;
+  }
+}
+
+}  // namespace media
+}  // namespace mojo