shaka-packager/packager/media/chunking/chunking_handler.h

// Copyright 2017 Google Inc. All rights reserved.
//
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file or at
// https://developers.google.com/open-source/licenses/bsd

#ifndef PACKAGER_MEDIA_CHUNKING_CHUNKING_HANDLER_
#define PACKAGER_MEDIA_CHUNKING_CHUNKING_HANDLER_

#include <atomic>
#include <queue>

#include "packager/base/logging.h"
#include "packager/media/base/media_handler.h"
#include "packager/media/public/chunking_params.h"

namespace shaka {
namespace media {

/// ChunkingHandler splits the samples into segments / subsegments based on the
/// specified chunking params.
/// This handler is a multi-in multi-out handler. If more than one input is
/// provided, there should be one and only one video stream; also, all inputs
/// should come from the same thread and are synchronized.
/// There can be multiple chunking handler running in different threads or even
/// different processes, we use the "consistent chunking algorithm" to make sure
/// the chunks in different streams are aligned without explicit communcating
/// with each other - which is not efficient and often difficult.
///
/// Consistent Chunking Algorithm:
///  1. Find the consistent chunkable boundary
///  Let the timestamps for video frames be (t1, t2, t3, ...). Then a
///  consistent chunkable boundary is simply the first chunkable boundary after
///  (tk / N) != (tk-1 / N), where '/' denotes integer division, and N is the
///  intended chunk duration.
///  2. Chunk only at the consistent chunkable boundary
///
/// This algorithm will make sure the chunks from different video streams are
/// aligned if they have aligned GoPs. However, this algorithm will only work
/// for video streams. To be able to chunk non video streams at similar
/// positions as video streams, ChunkingHandler is designed to accept one video
/// input and multiple non video inputs, the non video inputs are chunked when
/// the video input is chunked. If the inputs are synchronized - which is true
/// if the inputs come from the same demuxer, the video and non video chunks
/// are aligned.
class ChunkingHandler : public MediaHandler {
 public:
  explicit ChunkingHandler(const ChunkingParams& chunking_params);
  ~ChunkingHandler() override;

 protected:
  /// @name MediaHandler implementation overrides.
  /// @{
  Status InitializeInternal() override;
  Status Process(std::unique_ptr<StreamData> stream_data) override;
  Status OnFlushRequest(size_t input_stream_index) override;
  /// @}

 private:
  friend class ChunkingHandlerTest;

  ChunkingHandler(const ChunkingHandler&) = delete;
  ChunkingHandler& operator=(const ChunkingHandler&) = delete;

  // Processes main media sample and apply chunking if needed.
  Status ProcessMainMediaSample(const MediaSample* sample);

  // Processes and dispatches media sample.
  Status ProcessMediaSampleStreamData(const StreamData& media_data);

  // The (sub)segments are aligned and dispatched together.
  Status DispatchSegmentInfoForAllStreams();
  Status DispatchSubsegmentInfoForAllStreams();
  Status DispatchCueEventForAllStreams(std::shared_ptr<CueEvent> cue_event);

  const ChunkingParams chunking_params_;

  // The inputs are expected to come from the same thread.
  std::atomic<int64_t> thread_id_;

  // The video stream is the main stream; if there is only one stream, it is the
  // main stream. The chunking is based on the main stream.
  const size_t kInvalidStreamIndex = static_cast<size_t>(-1);
  size_t main_stream_index_ = kInvalidStreamIndex;
  // Segment and subsegment duration in main stream's time scale.
  int64_t segment_duration_ = 0;
  int64_t subsegment_duration_ = 0;

  class MediaSampleTimestampGreater {
   public:
    explicit MediaSampleTimestampGreater(
        const ChunkingHandler* const chunking_handler);

    // Comparison operator. Used by |media_samples_| priority queue below to
    // sort the media samples.
    bool operator()(const std::unique_ptr<StreamData>& lhs,
                    const std::unique_ptr<StreamData>& rhs) const;

   private:
    double GetSampleTimeInSeconds(
        const StreamData& media_sample_stream_data) const;

    const ChunkingHandler* const chunking_handler_ = nullptr;
  };
  MediaSampleTimestampGreater media_sample_comparator_;
  // Caches media samples and sort the samples.
  std::priority_queue<std::unique_ptr<StreamData>,
                      std::vector<std::unique_ptr<StreamData>>,
                      MediaSampleTimestampGreater>
      cached_media_sample_stream_data_;
  // Tracks number of cached samples in input streams.
  std::vector<size_t> num_cached_samples_;

  // Current segment index, useful to determine where to do chunking.
  int64_t current_segment_index_ = -1;
  // Current subsegment index, useful to determine where to do chunking.
  int64_t current_subsegment_index_ = -1;

  std::vector<std::shared_ptr<SegmentInfo>> segment_info_;
  std::vector<std::shared_ptr<SegmentInfo>> subsegment_info_;
  std::vector<uint32_t> time_scales_;
  // The end timestamp of the last dispatched sample.
  std::vector<int64_t> last_sample_end_timestamps_;

  struct Scte35EventTimestampGreater {
    bool operator()(const std::unique_ptr<StreamData>& lhs,
                    const std::unique_ptr<StreamData>& rhs) const;
  };
  // Captures all incoming SCTE35 events to identify chunking points. Events
  // will be removed from this queue one at a time as soon as the correct
  // chunking point is identified in the incoming samples.
  std::priority_queue<std::unique_ptr<StreamData>,
                      std::vector<std::unique_ptr<StreamData>>,
                      Scte35EventTimestampGreater>
      scte35_events_;
};

}  // namespace media
}  // namespace shaka

#endif  // PACKAGER_MEDIA_CHUNKING_CHUNKING_HANDLER_