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// Copyright 2021 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.
#ifndef CAST_STREAMING_RECEIVER_BASE_H_
#define CAST_STREAMING_RECEIVER_BASE_H_
#include <chrono>
#include "absl/types/span.h"
#include "cast/streaming/encoded_frame.h"
#include "cast/streaming/session_config.h"
#include "cast/streaming/ssrc.h"
#include "platform/api/time.h"
namespace openscreen {
namespace cast {
// The Cast Streaming Receiver, a peer corresponding to some Cast Streaming
// Sender at the other end of a network link.
//
// Cast Streaming is a transport protocol which divides up the frames for one
// media stream (e.g., audio or video) into multiple RTP packets containing an
// encrypted payload. The Receiver is the peer responsible for collecting the
// RTP packets, decrypting the payload, and re-assembling a frame that can be
// passed to a decoder and played out.
//
// A Sender ↔ Receiver pair is used to transport each media stream. Typically,
// there are two pairs in a normal system, one for the audio stream and one for
// video stream. A local player is responsible for synchronizing the playout of
// the frames of each stream to achieve lip-sync. See the discussion in
// encoded_frame.h for how the |reference_time| and |rtp_timestamp| of the
// EncodedFrames are used to achieve this.
class ReceiverBase {
public:
class Consumer {
public:
virtual ~Consumer();
// Called whenever one or more frames have become ready for consumption. The
// |next_frame_buffer_size| argument is identical to the result of calling
// AdvanceToNextFrame(), and so the Consumer only needs to prepare a buffer
// and call ConsumeNextFrame(). It may then call AdvanceToNextFrame() to
// check whether there are any more frames ready, but this is not mandatory.
// See usage example in class-level comments.
virtual void OnFramesReady(int next_frame_buffer_size) = 0;
};
ReceiverBase();
virtual ~ReceiverBase();
virtual const SessionConfig& config() const = 0;
virtual int rtp_timebase() const = 0;
virtual Ssrc ssrc() const = 0;
// Set the Consumer receiving notifications when new frames are ready for
// consumption. Frames received before this method is called will remain in
// the queue indefinitely.
virtual void SetConsumer(Consumer* consumer) = 0;
// Sets how much time the consumer will need to decode/buffer/render/etc., and
// otherwise fully process a frame for on-time playback. This information is
// used by the Receiver to decide whether to skip past frames that have
// arrived too late. This method can be called repeatedly to make adjustments
// based on changing environmental conditions.
//
// Default setting: kDefaultPlayerProcessingTime
virtual void SetPlayerProcessingTime(Clock::duration needed_time) = 0;
// Propagates a "picture loss indicator" notification to the Sender,
// requesting a key frame so that decode/playout can recover. It is safe to
// call this redundantly. The Receiver will clear the picture loss condition
// automatically, once a key frame is received (i.e., before
// ConsumeNextFrame() is called to access it).
virtual void RequestKeyFrame() = 0;
// Advances to the next frame ready for consumption. This may skip-over
// incomplete frames that will not play out on-time; but only if there are
// completed frames further down the queue that have no dependency
// relationship with them (e.g., key frames).
//
// This method returns kNoFramesReady if there is not currently a frame ready
// for consumption. The caller should wait for a Consumer::OnFramesReady()
// notification before trying again. Otherwise, the number of bytes of encoded
// data is returned, and the caller should use this to ensure the buffer it
// passes to ConsumeNextFrame() is large enough.
virtual int AdvanceToNextFrame() = 0;
// Returns the next frame, both metadata and payload data. The Consumer calls
// this method after being notified via OnFramesReady(), and it can also call
// this whenever AdvanceToNextFrame() indicates another frame is ready.
// |buffer| must point to a sufficiently-sized buffer that will be populated
// with the frame's payload data. Upon return |frame->data| will be set to the
// portion of the buffer that was populated.
virtual EncodedFrame ConsumeNextFrame(absl::Span<uint8_t> buffer) = 0;
// The default "player processing time" amount. See SetPlayerProcessingTime().
static constexpr std::chrono::milliseconds kDefaultPlayerProcessingTime{5};
// Returned by AdvanceToNextFrame() when there are no frames currently ready
// for consumption.
static constexpr int kNoFramesReady = -1;
};
} // namespace cast
} // namespace openscreen
#endif // CAST_STREAMING_RECEIVER_BASE_H_
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