# 基于AVPlayer播放格式化音频（C++）

#### 概述

AVPlayer可以用于播放格式化音频，支持WAV、MP3和FLAC等格式的音频。AVPlayer提供了ArkTS API和Native API，指导开发者使用AVPlayer的Native API实现播放格式化音频的功能，主要涉及基本播控、精准跳转、静音播放、倍速播放、音量控制、焦点管理、后台播放与接入播控中心、冷启动等开发场景。

本文是音频播放系列文章的第4篇，实现的功能效果如下：

![](https://media:201788187355207275 "点击放大") ![](https://media:201788187355680276 "点击放大") ![](https://media:201788187355863277 "点击放大")  

#### 场景分析

|场景名称|描述|实现方案|
|:-------------------------------------------------------------------------------------------------------------------------------------------|:----------------------------------------------|:-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
|[基础播控](#section1764813377511)|音频资源的加载、播放、暂停、退出等操作。|使用[avplayer](https://developer.huawei.com/consumer/cn/doc/harmonyos-references/capi-avplayer-h#概述)接口实现。|
|[跳转播放](#section16920851193717)|滑动进度条精准跳转到指定时间进行播放。|使用[Slider组件](https://developer.huawei.com/consumer/cn/doc/harmonyos-references/ts-basic-components-slider)实现进度条，在[onChange()](https://developer.huawei.com/consumer/cn/doc/harmonyos-references/ts-basic-components-slider#onchange)回调中触发进度调节获取目标时间，使用avplayer的[OH_AVPlayer_Seek()](https://developer.huawei.com/consumer/cn/doc/harmonyos-references/capi-avplayer-h#oh_avplayer_seek)接口，跳转到目标时间。|
|[静音播放](#section125715278533)|点击按钮设置静音播放。|使用avplayer的[OH_AVPlayer_SetVolume()](https://developer.huawei.com/consumer/cn/doc/harmonyos-references/capi-avplayer-h#oh_avplayer_setvolume)接口设置音量为0，进入静音状态。|
|[切换歌曲播放](#section590418431566)|点击上一首或下一首或歌单列表中的歌曲进行不同歌曲播放。|使用[OH_AVPlayer_Reset()](https://developer.huawei.com/consumer/cn/doc/harmonyos-references/capi-avplayer-h#oh_avplayer_reset)接口重置播放器状态，给avplayer的fd或fdSrc属性赋值为新的歌曲资源，实现播放不同的歌曲功能。|
|[倍速设置](#section189460361122)|滑动调节面板调节播放速度。|使用[OH_AVPlayer_SetPlaybackRate()](https://developer.huawei.com/consumer/cn/doc/harmonyos-references/capi-avplayer-h#oh_avplayer_setplaybackspeed)接口设置播放倍速。|
|[音量设置](#section88718617116)|滑动调节面板调节播放音量。|使用[OH_AVPlayer_SetVolume()](https://developer.huawei.com/consumer/cn/doc/harmonyos-references/capi-avplayer-h#oh_avplayer_setvolume)设置播放音量。|
|[接入播控中心](https://developer.huawei.com/consumer/cn/doc/best-practices/bpta-playing-pcm-audio-based-audiorenderer#section06660114245)|通过播控中心，控制播放、暂停、切换音频、调整播放进度、切换循环模式|具体原理、方案和开发步骤参考[接入播控中心](https://developer.huawei.com/consumer/cn/doc/best-practices/bpta-playing-pcm-audio-based-audiorenderer#section06660114245)。本篇文章不再赘述。|
|[后台播放](https://developer.huawei.com/consumer/cn/doc/best-practices/bpta-playing-pcm-audio-based-audiorenderer#section1749719114143)|音频切换到后台播放。|具体原理、方案和开发步骤参考[后台播放](https://developer.huawei.com/consumer/cn/doc/best-practices/bpta-playing-pcm-audio-based-audiorenderer#section1749719114143)。本篇文章不再赘述。|
|[接入播控中心冷启动和历史歌单](https://developer.huawei.com/consumer/cn/doc/best-practices/bpta-playing-pcm-audio-based-audiorenderer#section476545143517)|应用退出后，播控中心显示历史歌单，点击播控中心播放按钮拉起应用播放，或者点击歌单拉起应用播放。|具体原理、方案和开发步骤参考[接入播控中心冷启动和历史歌单](https://developer.huawei.com/consumer/cn/doc/best-practices/bpta-playing-pcm-audio-based-audiorenderer#section476545143517)。本篇文章不再赘述。|

#### 基础播控

#### 场景描述

通过[avplayer](https://developer.huawei.com/consumer/cn/doc/harmonyos-references/capi-avplayer-h#概述)接口实现核心音频播放控制能力，包括音频资源加载、播放、暂停、停止及退出等操作。

![](https://media:201788187356106278 "点击放大")  

#### 实现原理

核心原理是使用[avplayer](https://developer.huawei.com/consumer/cn/doc/harmonyos-references/capi-avplayer-h#概述)接口实现播放、暂停等功能，需要特别注意的是，播放器在执行不同的操作前，必须要保证此时处于正确的状态，比如执行播放操作前，只有当前状态在prepared/paused/completed时，才能正确执行，否则系统可能会抛出异常或生成其他未定义的行为。AVPlayer的播放状态和不同接口间的关系参考[使用AVPlayer播放音频](https://developer.huawei.com/consumer/cn/doc/harmonyos-guides/using-ndk-avplayer-for-playback)一节中的播放状态变化示意图。

主要的开发步骤如下：

1. 开发者可以通过[OH_AVPlayer_Create()](https://developer.huawei.com/consumer/cn/doc/harmonyos-references/capi-avplayer-h#oh_avplayer_create)构建一个avplayer实例，创建成功后，此时播放器处于idle状态。
2. 使用[OH_AVPlayer_SetOnInfoCallback()](https://developer.huawei.com/consumer/cn/doc/harmonyos-references/capi-avplayer-h#oh_avplayer_setoninfocallback)注册状态变化的回调，对状态变化做出响应。  
   ![](https://media:201788187356138279)  
   因为AVPlayer播放器的接口是否能正常执行和当前的播放器状态有必然联系，建议开发者务必使用[OH_AVPlayer_SetOnInfoCallback()](https://developer.huawei.com/consumer/cn/doc/harmonyos-references/capi-avplayer-h#oh_avplayer_setoninfocallback)注册状态变化的回调获取当前状态，保证在正确的状态下执行对应操作。以免发生异常，影响开发效率。
3. 使用[OH_AVPlayer_SetOnErrorCallback()](https://developer.huawei.com/consumer/cn/doc/harmonyos-references/capi-avplayer-h#oh_avplayer_setonerrorcallback)接口设置异常信息的回调，发生异常后，监听错误事件，可以快速根据报错信息进行定位。
4. 通过[OH_AVPlayer_SetFDSource()](https://developer.huawei.com/consumer/cn/doc/harmonyos-references/capi-avplayer-h#oh_avplayer_setfdsource)设置播放资源，设置成功后，播放器会进入initialized状态。
5. 执行[OH_AVPlayer_Prepare()](https://developer.huawei.com/consumer/cn/doc/harmonyos-references/capi-avplayer-h#oh_avplayer_prepare)接口准备播放音频，播放器会进入prepared状态。
6. 执行[OH_AVPlayer_Play()](https://developer.huawei.com/consumer/cn/doc/harmonyos-references/capi-avplayer-h#oh_avplayer_play)接口，播放音频资源。  
   ![](https://media:201788187356169280)  
   第4步设置完url、fdSrc等属性后，播放器并不是就立刻进入initialized状态；第5步执行完[OH_AVPlayer_Prepare()](https://developer.huawei.com/consumer/cn/doc/harmonyos-references/capi-avplayer-h#oh_avplayer_prepare)接口，播放器也不是立刻进入prepared，都是需在[OH_AVPlayer_SetOnInfoCallback()](https://developer.huawei.com/consumer/cn/doc/harmonyos-references/capi-avplayer-h#oh_avplayer_setoninfocallback)注册状态变化的回调中，监听到播放器成功触发至initialized状态后，才能执行下一步的操作，否则接口会执行异常。

   7. 执行[OH_AVPlayer_Pause()](https://developer.huawei.com/consumer/cn/doc/harmonyos-references/capi-avplayer-h#oh_avplayer_pause)接口，暂停音频资源。

   8. 执行[OH_AVPlayer_Stop()](https://developer.huawei.com/consumer/cn/doc/harmonyos-references/capi-avplayer-h#oh_avplayer_stop)接口，停止播放音频资源。

9. 执行[OH_AVPlayer_Release()](https://developer.huawei.com/consumer/cn/doc/harmonyos-references/capi-avplayer-h#oh_avplayer_release)接口，销毁播放资源。  

#### 开发步骤

1. 通过[OH_AVPlayer_Create()](https://developer.huawei.com/consumer/cn/doc/harmonyos-references/capi-avplayer-h#oh_avplayer_create)创建一个AVPlayer实例。

```
void AVPlayer::InitPlayer() {
    // Check the residual status of the previous player
    if (ohAVPlayer != nullptr) {
        OH_LOG_INFO(LOG_APP, "Previous audio player remained and release it.");
        ReleasePlayer();
    }

    ohAVPlayer = OH_AVPlayer_Create();
    if (ohAVPlayer == nullptr) {
        OH_LOG_ERROR(LOG_APP, "Create AVPlayer instance failed.");
        return;
    }
    // ...

    OH_LOG_INFO(LOG_APP, "Init player successfully.");
}
```

2. 使用[OH_AVPlayer_SetOnInfoCallback()](https://developer.huawei.com/consumer/cn/doc/harmonyos-references/capi-avplayer-h#oh_avplayer_setoninfocallback)注册状态变化的回调，对状态变化做出响应。

```
// Define OHAVPlayerOnInfoCallback function
static void OHAVPlayerOnInfoCallback(OH_AVPlayer *player, AVPlayerOnInfoType type, OH_AVFormat *infoBody,
                                     [[maybe_unused]] void *userData) {
    if (player == nullptr) {
        OH_LOG_ERROR(LOG_APP, "OHAVPlayerOnInfoCallback: the player is null.");
        return;
    }
    switch (type) {
    case AV_INFO_TYPE_STATE_CHANGE: {
        int32_t playerState = 0;
        int32_t stateChangeReason = 0;
        OH_AVFormat_GetIntValue(infoBody, OH_PLAYER_STATE, &playerState);
        OH_AVFormat_GetIntValue(infoBody, OH_PLAYER_STATE_CHANGE_REASON, &stateChangeReason);
        OH_LOG_INFO(LOG_APP, "The player state has been changed, state: %{public}d, reason: %{public}d.", playerState,
                    stateChangeReason);
        OHAVPlayerOnStateChange(player, playerState);
    } break;
     // ...
}
```

```
// On player state change and process it
static void OHAVPlayerOnStateChange(OH_AVPlayer *player, int32_t playerState) {
    AVPlayer::GetInstance().PlayerState = playerState;
    switch (playerState) {
    case AV_IDLE:
        OH_LOG_INFO(LOG_APP, "playerState: AV_IDLE.");
        break;
    case AV_INITIALIZED:
        // ...
            // Prepare player
            ret = OH_AVPlayer_Prepare(player);
            // ...
        break;
    case AV_PREPARED:
        OH_LOG_INFO(LOG_APP, "playerState: AV_PREPARED.");
        // ...
            if (AVPlayer::GetInstance().WaitPlay) {
                AVPlayer::GetInstance().PlaySong();
            }
            // ...
        break;
        // ...
    default:
        break;
    }
}
```

3. 使用[OH_AVPlayer_SetOnErrorCallback()](https://developer.huawei.com/consumer/cn/doc/harmonyos-references/capi-avplayer-h#oh_avplayer_setonerrorcallback)设置异常信息的回调，发生异常后，监听错误事件。

```
// Define OHAVPlayerOnErrorCallback function
static void OHAVPlayerOnErrorCallback([[maybe_unused]] OH_AVPlayer *player, int32_t errCode, const char *errMsg,
                                      [[maybe_unused]] void *userData) {
    OH_LOG_ERROR(LOG_APP, "OHAVPlayerOnErrorCallback, errCode: %{public}d, errMsg: %{public}s.", errCode, errMsg);
}
```

4. 通过[OH_AVPlayer_SetFDSource()](https://developer.huawei.com/consumer/cn/doc/harmonyos-references/capi-avplayer-h#oh_avplayer_setfdsource)设置播放资源。

```
void AVPlayer::LoadSongInfo(uint32_t songFd, uint32_t songFileSize, uint32_t songFileOffset) {
    if (ohAVPlayer == nullptr) {
        OH_LOG_ERROR(LOG_APP, "The ohAVPlayer is null.");
        return;
    }

    AVPlayerState playerState = AV_IDLE;

    auto ret = OH_AVPlayer_GetState(ohAVPlayer, &playerState);
    if (ret != AV_ERR_OK) {
        OH_LOG_ERROR(LOG_APP, "Get player state failed, ret: %{public}d", ret);
        return;
    }

    // When the application loads or plays the first song for the first time, the player does not need to be reset
    // In addition, the player cannot be reset in idle state, otherwise an error will be reported
    // When playing for the first time, the player is in idle state after creation.
    if (playerState != AV_IDLE) {
        ret = OH_AVPlayer_Reset(ohAVPlayer);
        if (ret != AV_ERR_OK) {
            OH_LOG_ERROR(LOG_APP, "Reset player failed, ret: %{public}d", ret);
            return;
        }
    }

    ret = OH_AVPlayer_SetFDSource(ohAVPlayer, songFd, songFileOffset, songFileSize);
    if (ret != AV_ERR_OK) {
        OH_LOG_ERROR(LOG_APP, "Load song information failed, ret: %{public}d", ret);
        return;
    }

    OH_LOG_INFO(LOG_APP,
                "Load song information successfully. "
                "Song fd: %{public}d, "
                "file size: %{public}d, "
                "file offset: %{public}d.",
                songFd, songFileSize, songFileOffset);
}
```

5. 执行[OH_AVPlayer_Prepare()](https://developer.huawei.com/consumer/cn/doc/harmonyos-references/capi-avplayer-h#oh_avplayer_prepare)接口准备播放音频。

```
// Prepare player
ret = OH_AVPlayer_Prepare(player);
if (ret != AV_ERR_OK) {
    OH_LOG_ERROR(LOG_APP, "Prepare player failed, ret: %{public}d", ret);
    (void)OH_AVPlayer_Release(player);
    player = nullptr;
}
```

6. 执行[OH_AVPlayer_Play()](https://developer.huawei.com/consumer/cn/doc/harmonyos-references/capi-avplayer-h#oh_avplayer_play)接口，播放音频资源。

```
void AVPlayer::PlaySong() {
    if (ohAVPlayer == nullptr) {
        OH_LOG_ERROR(LOG_APP, "The ohAVPlayer is null.");
        return;
    }
    if (PlayerState != AV_PREPARED && PlayerState != AV_PAUSED && PlayerState != AV_STOPPED &&
        PlayerState != AV_COMPLETED) {
        WaitPlay = true;
        return;
    }
    auto ret = OH_AVPlayer_Play(ohAVPlayer);
    WaitPlay = false;
    if (ret != AV_ERR_OK) {
        OH_LOG_ERROR(LOG_APP, "Play song failed, ret: %{public}d", ret);
        return;
    }
    OH_LOG_INFO(LOG_APP, "Play song successfully.");
}
```

7. 执行[OH_AVPlayer_Pause()](https://developer.huawei.com/consumer/cn/doc/harmonyos-references/capi-avplayer-h#oh_avplayer_pause)接口，暂停播放音频。

```
void AVPlayer::PauseSong() {
    if (ohAVPlayer == nullptr) {
        OH_LOG_ERROR(LOG_APP, "The ohAVPlayer is null.");
        return;
    }
    auto ret = OH_AVPlayer_Pause(ohAVPlayer);
    if (ret != AV_ERR_OK) {
        OH_LOG_ERROR(LOG_APP, "Pause song failed, ret: %{public}d", ret);
        return;
    }

    OH_LOG_INFO(LOG_APP, "Pause song successfully.");
}
```

8. 执行[OH_AVPlayer_Stop()](https://developer.huawei.com/consumer/cn/doc/harmonyos-references/capi-avplayer-h#oh_avplayer_stop)接口，停止播放音频资源。

```
void AVPlayer::StopSong() {
    if (ohAVPlayer == nullptr) {
        OH_LOG_ERROR(LOG_APP, "The ohAVPlayer is null.");
        return;
    }
    auto ret = OH_AVPlayer_Stop(ohAVPlayer);
    if (ret != AV_ERR_OK) {
        OH_LOG_ERROR(LOG_APP, "Stop song failed, ret: %{public}d", ret);
        return;
    }
    OH_LOG_INFO(LOG_APP, "Stop song successfully.");
}
```

9. 执行[OH_AVPlayer_Release()](https://developer.huawei.com/consumer/cn/doc/harmonyos-references/capi-avplayer-h#oh_avplayer_release)接口，销毁播放资源。

```
void AVPlayer::ReleasePlayer() {
    if (ohAVPlayer == nullptr) {
        OH_LOG_ERROR(LOG_APP, "The ohAVPlayer is null.");
        return;
    }
    auto ret = OH_AVPlayer_Release(ohAVPlayer);
    if (ret != AV_ERR_OK) {
        OH_LOG_ERROR(LOG_APP, "Release player failed, ret: %{public}d", ret);
        return;
    }
    ohAVPlayer = nullptr;
    OH_LOG_INFO(LOG_APP, "Release player successfully.");
}
```

#### 跳转播放

#### 场景描述

通过点击或拖动进度条精准跳转到指定时间进行播放。

![](https://media:201788187356616281 "点击放大")  

#### 实现原理

使用[Slider组件](https://developer.huawei.com/consumer/cn/doc/harmonyos-references/ts-basic-components-slider)实现进度条，在[onChange()](https://developer.huawei.com/consumer/cn/doc/harmonyos-references/ts-basic-components-slider#onchange)回调中触发进度调节获取目标时间，使用AVPlayer的[seek()](https://developer.huawei.com/consumer/cn/doc/harmonyos-references/arkts-apis-media-avplayer#seek9)接口，跳转到目标时间。  

#### 开发步骤

使用avplayer的[OH_AVPlayer_Seek()](https://developer.huawei.com/consumer/cn/doc/harmonyos-references/capi-avplayer-h#oh_avplayer_seek)接口，跳转到目标时间。

```
void AVPlayer::SeekPlaySong(uint32_t timeStamp) {
    if (ohAVPlayer == nullptr) {
        OH_LOG_ERROR(LOG_APP, "The ohAVPlayer is null.");
        return;
    }
    auto ret = OH_AVPlayer_Seek(ohAVPlayer, timeStamp, AV_SEEK_CLOSEST);
    if (ret != AV_ERR_OK) {
        OH_LOG_ERROR(LOG_APP, "Seek song failed, ret: %{public}d", ret);
        return;
    }
    OH_LOG_INFO(LOG_APP, "Seek song successfully.");
}
```

#### 静音播放

#### 场景描述

通过界面按钮快捷切换音频播放静音状态，实现一键开启或关闭静音。

![](https://media:201788187356912282 "点击放大")  

#### 实现原理

使用avplayer的[OH_AVPlayer_SetVolume()](https://developer.huawei.com/consumer/cn/doc/harmonyos-references/capi-avplayer-h#oh_avplayer_setvolume)接口设置音量为0，进入静音模式状态。  

#### 开发步骤

调用avplayer的[OH_AVPlayer_SetVolume()](https://developer.huawei.com/consumer/cn/doc/harmonyos-references/capi-avplayer-h#oh_avplayer_setvolume)接口，如果确定开启静音模式，则将音量设置成0。

```
void AVPlayer::SetSilentMode(bool isSilentMode) {
    if (ohAVPlayer == nullptr) {
        OH_LOG_ERROR(LOG_APP, "The ohAVPlayer is null.");
        return;
    }
    // If the isSilentMode is true, set the volume to 0; Otherwise, restore the latest volume value
    float volume = isSilentMode ? 0 : lastVolume;
    auto ret = OH_AVPlayer_SetVolume(ohAVPlayer, volume, volume);
    if (ret != AV_ERR_OK) {
        OH_LOG_ERROR(LOG_APP, "SetSilentMode: set app volume failed, ret: %{public}d", ret);
        return;
    }
    OH_LOG_INFO(LOG_APP, "Set silent mode successfully.");
}
```

#### 切换歌曲播放

#### 场景描述

点击上一首或下一首或歌单列表中的歌曲进行不同歌曲播放。

![](https://media:201788187357150283 "点击放大")  

#### 实现原理

使用[OH_AVPlayer_Reset()](https://developer.huawei.com/consumer/cn/doc/harmonyos-references/capi-avplayer-h#oh_avplayer_reset)接口重置播放器状态，给AVPlayer的fd或fdSrc属性赋值为新的歌曲资源，实现播放不同歌曲的功能。  

#### 开发步骤

1. 停止当前播放的歌曲。

```
void AVPlayer::StopSong() {
    if (ohAVPlayer == nullptr) {
        OH_LOG_ERROR(LOG_APP, "The ohAVPlayer is null.");
        return;
    }
    auto ret = OH_AVPlayer_Stop(ohAVPlayer);
    if (ret != AV_ERR_OK) {
        OH_LOG_ERROR(LOG_APP, "Stop song failed, ret: %{public}d", ret);
        return;
    }
    OH_LOG_INFO(LOG_APP, "Stop song successfully.");
}
```

2. 用[OH_AVPlayer_Reset()](https://developer.huawei.com/consumer/cn/doc/harmonyos-references/capi-avplayer-h#oh_avplayer_reset)接口重置播放器状态。

```
ret = OH_AVPlayer_Reset(ohAVPlayer);
if (ret != AV_ERR_OK) {
    OH_LOG_ERROR(LOG_APP, "Reset player failed, ret: %{public}d", ret);
    return;
}
```

3.使用[OH_AVPlayer_SetFDSource()](https://developer.huawei.com/consumer/cn/doc/harmonyos-references/capi-avplayer-h#oh_avplayer_setfdsource)设置播放资源。

```
void AVPlayer::LoadSongInfo(uint32_t songFd, uint32_t songFileSize, uint32_t songFileOffset) {
    if (ohAVPlayer == nullptr) {
        OH_LOG_ERROR(LOG_APP, "The ohAVPlayer is null.");
        return;
    }

    AVPlayerState playerState = AV_IDLE;

    auto ret = OH_AVPlayer_GetState(ohAVPlayer, &playerState);
    if (ret != AV_ERR_OK) {
        OH_LOG_ERROR(LOG_APP, "Get player state failed, ret: %{public}d", ret);
        return;
    }

    // When the application loads or plays the first song for the first time, the player does not need to be reset
    // In addition, the player cannot be reset in idle state, otherwise an error will be reported
    // When playing for the first time, the player is in idle state after creation.
    if (playerState != AV_IDLE) {
        ret = OH_AVPlayer_Reset(ohAVPlayer);
        if (ret != AV_ERR_OK) {
            OH_LOG_ERROR(LOG_APP, "Reset player failed, ret: %{public}d", ret);
            return;
        }
    }

    ret = OH_AVPlayer_SetFDSource(ohAVPlayer, songFd, songFileOffset, songFileSize);
    if (ret != AV_ERR_OK) {
        OH_LOG_ERROR(LOG_APP, "Load song information failed, ret: %{public}d", ret);
        return;
    }

    OH_LOG_INFO(LOG_APP,
                "Load song information successfully. "
                "Song fd: %{public}d, "
                "file size: %{public}d, "
                "file offset: %{public}d.",
                songFd, songFileSize, songFileOffset);
}
```

#### 倍速设置

#### 场景描述

滑动倍速调节面板调节播放速度。

![](https://media:201788187357486284 "点击放大")  

#### 实现原理

通过调节面板获取目标速度值，传入[OH_AVPlayer_SetPlaybackRate()](https://developer.huawei.com/consumer/cn/doc/harmonyos-references/capi-avplayer-h#oh_avplayer_setplaybackrate)接口中，实现设置播放速度的功能。  

#### 开发步骤

1. 通过调节面板获取速度值，传入[OH_AVPlayer_SetPlaybackRate()](https://developer.huawei.com/consumer/cn/doc/harmonyos-references/capi-avplayer-h#oh_avplayer_setplaybackrate)接口中。

```
Slider({
  value: this.speed,
  min: 0.25,
  max: 2,
  step: 0.25,
  style: SliderStyle.OutSet
})
  .layoutWeight(1)
  .showTips(true, this.speed.toString())
  .showSteps(true)
  .onChange((value: number, mode: SliderChangeMode) => {
    this.speed = value;
    MediaControlCenter.getInstance().setSpeed(this.speed);
    console.info('value:' + value + 'mode:' + mode.toString());
  })
```

2. 使用[OH_AVPlayer_SetPlaybackRate()](https://developer.huawei.com/consumer/cn/doc/harmonyos-references/capi-avplayer-h#oh_avplayer_setplaybackrate)接口设置播放倍速。

```
void AVPlayer::SetPlayingSpeed(float speed) {
    if (ohAVPlayer == nullptr) {
        OH_LOG_ERROR(LOG_APP, "The ohAVPlayer is null.");
        return;
    }
    auto ret = OH_AVPlayer_SetPlaybackRate(ohAVPlayer, speed);
    if (ret != AV_ERR_OK) {
        OH_LOG_ERROR(LOG_APP, "Set playing speed failed, ret: %{public}d", ret);
        return;
    }
    OH_LOG_INFO(LOG_APP, "Set playing speed successfully.");
}
```

#### 音量设置

#### 场景描述

滑动音量调节面板调节播放音量。

![](https://media:201788187357758285 "点击放大")  

#### 实现原理

通过调节面板获取目标音量值，输入到[OH_AVPlayer_SetVolume()](https://developer.huawei.com/consumer/cn/doc/harmonyos-references/capi-avplayer-h#oh_avplayer_setvolume)接口中，实现设置播放音量的功能。  

#### 开发步骤

1. 通过调节面板获取音量值，传入[OH_AVPlayer_SetVolume()](https://developer.huawei.com/consumer/cn/doc/harmonyos-references/capi-avplayer-h#oh_avplayer_setvolume)接口中。

```
Slider({
  value: this.volume,
  min: 0,
  max: 1,
  step: 0.1,
  style: SliderStyle.OutSet
})
  .showTips(false)
  .layoutWeight(1)
  .onChange((value: number, mode: SliderChangeMode) => {
    this.volume = value;
    if (this.volume === 0) {
      this.isSilentMode = true
    } else {
      this.isSilentMode = false;
    }
  })
```

2. 使用[OH_AVPlayer_SetVolume()](https://developer.huawei.com/consumer/cn/doc/harmonyos-references/capi-avplayer-h#oh_avplayer_setvolume)设置播放音量。

```
void AVPlayer::SetPlayingVolume(float volume) {
    if (ohAVPlayer == nullptr) {
        OH_LOG_ERROR(LOG_APP, "The ohAVPlayer is null.");
        return;
    }
    auto ret = OH_AVPlayer_SetVolume(ohAVPlayer, volume, volume);
    if (ret != AV_ERR_OK) {
        OH_LOG_ERROR(LOG_APP, "Set app volume failed, ret: %{public}d", ret);
        return;
    }
    lastVolume = volume;
    OH_LOG_INFO(LOG_APP, "Set app volume successfully.");
}
```

#### 常见问题

#### 执行AVPlayer的方法时失败，返回错误码3

问题现象

在调用AVPlayer的[OH_AVPlayer_Prepare()](https://developer.huawei.com/consumer/cn/doc/harmonyos-references/capi-avplayer-h#oh_avplayer_prepare)、[OH_AVPlayer_Play()](https://developer.huawei.com/consumer/cn/doc/harmonyos-references/capi-avplayer-h#oh_avplayer_play)、[OH_AVPlayer_Stop()](https://developer.huawei.com/consumer/cn/doc/harmonyos-references/capi-avplayer-h#oh_avplayer_stop)等方法时，会执行失败，返回错误码3。如以下场景。

* 设置完url、fdSrc等属性后，代码下一行就立刻执行[OH_AVPlayer_Prepare()](https://developer.huawei.com/consumer/cn/doc/harmonyos-references/capi-avplayer-h#oh_avplayer_prepare)接口，执行出错，返回错误码3。
* 同样，执行完[OH_AVPlayer_Prepare()](https://developer.huawei.com/consumer/cn/doc/harmonyos-references/capi-avplayer-h#oh_avplayer_prepare)接口，代码下一行立刻执行[OH_AVPlayer_Play()](https://developer.huawei.com/consumer/cn/doc/harmonyos-references/capi-avplayer-h#oh_avplayer_play)接口，执行出错，返回错误码3。

可能原因

通过[OH_AVErrCode](https://developer.huawei.com/consumer/cn/doc/harmonyos-references/capi-native-averrors-h#oh_averrcode)错误码查出，错误码3对应的信息为"AV_ERR_INVALID_VAL "，可能得原因是AVPlayer的当前状态不支持此操作。AVPlayer播放器在执行不同的操作前，必须要保证此时处于正确的状态，比如执行播放操作前，只有当前状态在prepared/paused/completed时，才能正确执行。针对问题现象中举例的两种场景，其错误的原因可能如下。

* 设置完url、fdSrc等属性后，AVPlayer并不是就立刻进入initialized状态，如果设置完url属性后就立刻执行[OH_AVPlayer_Prepare()](https://developer.huawei.com/consumer/cn/doc/harmonyos-references/capi-avplayer-h#oh_avplayer_prepare)接口，当代码运行此行时，AVPlayer的播放状态可能还是处于idle的状态，并没有变成initialized，这时就可能产生此错误。
* 同样，执行完[OH_AVPlayer_Prepare()](https://developer.huawei.com/consumer/cn/doc/harmonyos-references/capi-avplayer-h#oh_avplayer_prepare)接口，AVPlayer也不是立刻进入prepared状态，如果此时立刻执行[OH_AVPlayer_Play()](https://developer.huawei.com/consumer/cn/doc/harmonyos-references/capi-avplayer-h#oh_avplayer_play)接口，AVPlayer的播放状态可能还没有变成prepared状态，执行就可能报错。

解决方案

1. 先了解在AVPlayer的不同播放状态下，可以执行哪些接口。熟悉AVPlayer的播放状态和不同接口间的关系，可以参考[使用AVPlayer播放音频](https://developer.huawei.com/consumer/cn/doc/harmonyos-guides/using-ndk-avplayer-for-playback)一节中的播放状态变化示意图一节中的播放状态变化示意图。

2. 保证在在正确的播放状态下，执行对应的接口。建议开发者务必使用[OH_AVPlayer_SetOnInfoCallback()](https://developer.huawei.com/consumer/cn/doc/harmonyos-references/capi-avplayer-h#oh_avplayer_setoninfocallback)注册状态变化的回调，当监听到AVPlayer的播放状态到达目标状态时，执行对应的接口。当监听到AVPlayer处于initialized状态时，再执行[OH_AVPlayer_Prepare()](https://developer.huawei.com/consumer/cn/doc/harmonyos-references/capi-avplayer-h#oh_avplayer_prepare)接口，监听到AVPlayer处于prepared状态时，再执行[OH_AVPlayer_Play()](https://developer.huawei.com/consumer/cn/doc/harmonyos-references/capi-avplayer-h#oh_avplayer_play)接口。

```
// On player state change and process it
static void OHAVPlayerOnStateChange(OH_AVPlayer *player, int32_t playerState) {
    AVPlayer::GetInstance().PlayerState = playerState;
    switch (playerState) {
    case AV_IDLE:
        OH_LOG_INFO(LOG_APP, "playerState: AV_IDLE.");
        break;
    case AV_INITIALIZED:
        // ...
            // Prepare player
            ret = OH_AVPlayer_Prepare(player);
            // ...
        break;
    case AV_PREPARED:
        OH_LOG_INFO(LOG_APP, "playerState: AV_PREPARED.");
        // ...
            if (AVPlayer::GetInstance().WaitPlay) {
                AVPlayer::GetInstance().PlaySong();
            }
            // ...
        break;
        // ...
    default:
        break;
    }
}
```

#### 示例代码

* [基于AVPlayer播放格式化音频（C++）](https://gitcode.com/HarmonyOS_Samples/avplayer-play-formatted-audio-cpp)