1 /* 2 * Copyright (C) 2022 The Android Open Source Project 3 * 4 * Licensed under the Apache License, Version 2.0 (the "License"); 5 * you may not use this file except in compliance with the License. 6 * You may obtain a copy of the License at 7 * 8 * http://www.apache.org/licenses/LICENSE-2.0 9 * 10 * Unless required by applicable law or agreed to in writing, software 11 * distributed under the License is distributed on an "AS IS" BASIS, 12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 13 * See the License for the specific language governing permissions and 14 * limitations under the License. 15 */ 16 17 #pragma once 18 19 #include <cstdint> 20 21 namespace android::audioflinger { 22 23 /** 24 * MonotonicFrameCounter 25 * 26 * Advances a monotonic frame count based on input timestamp pairs (frames, time). 27 * It takes into account a possible flush, which will "reset" the frames to 0. 28 * 29 * This class is used to drive VolumeShaper volume automation. 30 * 31 * The timestamps provided in updateAndGetMonotonicFrameCount should 32 * be of sufficient granularity for the purpose at hand. Currently no temporal 33 * extrapolation is done. 34 * 35 * This class is not thread safe. 36 */ 37 class MonotonicFrameCounter { 38 public: 39 /** 40 * Receives a new timestamp pair (frames, time) and returns a monotonic frameCount. 41 * 42 * \param newFrameCount the frameCount currently played. 43 * \param newTime the time corresponding to the frameCount. 44 * \return a monotonic frame count usable for automation timing. 45 */ 46 int64_t updateAndGetMonotonicFrameCount(int64_t newFrameCount, int64_t newTime); 47 48 /** 49 * Notifies when a flush occurs, whereupon the received frameCount sequence restarts at 0. 50 * 51 * \return the last reported frameCount. 52 */ 53 int64_t onFlush(); 54 55 /** 56 * Returns the received (input) frameCount to reported (output) frameCount offset. 57 * 58 * This offset is sufficient to ensure monotonicity after flush is called, 59 * suitability for any other purpose is *not* guaranteed. 60 */ getOffsetFrameCount()61 [[nodiscard]] int64_t getOffsetFrameCount() const { return mOffsetFrameCount; } 62 63 /** 64 * Returns the last received frameCount. 65 */ getLastReceivedFrameCount()66 [[nodiscard]] int64_t getLastReceivedFrameCount() const { 67 return mLastReceivedFrameCount; 68 } 69 70 /** 71 * Returns the last reported frameCount from updateAndGetMonotonicFrameCount(). 72 */ getLastReportedFrameCount()73 [[nodiscard]] int64_t getLastReportedFrameCount() const { 74 // This is consistent after onFlush(). 75 return mOffsetFrameCount + mLastReceivedFrameCount; 76 } 77 78 private: 79 int64_t mOffsetFrameCount = 0; 80 int64_t mLastReceivedFrameCount = 0; 81 }; 82 83 } // namespace android::audioflinger 84