解决ReplayKit开启Microphone，AVAssetWriter写入失败

最近在做直播内录制视频分享的功能，便尝试使用了ReplayKit，期间遇到一些问题，在这里记录下来。

在尝试过程中，遇到两种场景：

场景1

1. 开启 AVAssetWriter (包含 Audio / Video Writer Input)
2. 使用RPScreenRecorder开始录制（不启动Microphone）
3. 录制成功并成功获得视频

场景2

1. 开启 AVAssetWriter (包含 Audio / Video Writer Input)
2. 使用RPScreenRecorder开始录制（启动Microphone）
3. 录制失败

针对第二种情况，网上相应的解决方案很少（不知道是不是只有我遇到了）。所以在经过n次google(stackoverflow上的解决方案)和自己尝试之后，终于成功解决。下面是我的代码

    if (openMic) {
        [RPScreenRecorder sharedRecorder].microphoneEnabled = YES;
    } else {
        [RPScreenRecorder sharedRecorder].microphoneEnabled = NO;
    }
    [self.videoWriter startWriting];
    __weak typeof(self) weakSelf = self;
    [[RPScreenRecorder sharedRecorder] startCaptureWithHandler:^(CMSampleBufferRef _Nonnull sampleBuffer,RPSampleBufferType bufferType, NSError *_Nullable error) {
        __strong typeof(weakSelf) strongSelf = weakSelf;
        if (!CMSampleBufferDataIsReady(sampleBuffer)) {
            return;
        }
        if (strongSelf.videoWriter.status == AVAssetWriterStatusFailed) {
            NSLog(@"[录屏]AVAssetWriterStatusFailed");
            return;
        }
        if (strongSelf.videoWriter.status == AVAssetWriterStatusWriting) {
            if (bufferType == RPSampleBufferTypeVideo) {
                if (!strongSelf.startedSession) {
                    [strongSelf.videoWriter startSessionAtSourceTime:CMSampleBufferGetPresentationTimeStam(sampleBuffer)];
                    strongSelf.startedSession = YES;
                    NSLog(@"[录屏]开启session 视频处");
                }
                if (CMTimeCompare(kCMTimeInvalid, strongSelf.firstVideoFramTime) == 0) {
                    strongSelf.firstVideoFramTime = CMSampleBufferGetPresentationTimeStamp(sampleBuffer);
                }
                if ([strongSelf.videoWriterInput isReadyForMoreMediaData]) {
                    @try {
                        [strongSelf.videoWriterInput appendSampleBuffer:sampleBuffer];
                        NSLog(@"[录屏]写入视频数据");
                    } @catch (NSException *exception) {
                        NSLog(@"[录屏]写入视频数据失败");
                    }
                }
            }
            if (bufferType == RPSampleBufferTypeAudioApp || bufferType == RPSampleBufferTypeAudioMic) {
                // 可以在这里做一些过滤操作
                // if (onlyMicAudio && bufferType == RPSampleBufferTypeAudioApp) {
                //     return;
                // }
                
                if (CMTimeCompare(kCMTimeInvalid, strongSelf.firstVideoFramTime) == 0 || CMTimeCompar(strongSelf.firstVideoFramTime, CMSampleBufferGetPresentationTimeStamp(sampleBuffer)) == 1) {
                    return;
                }
                if (!strongSelf.startedSession) {
                    [strongSelf.videoWriter startSessionAtSourceTime:CMSampleBufferGetPresentationTimeStam(sampleBuffer)];
                    strongSelf.startedSession = YES;
                    NSLog(@"[录屏]开启session 音频处");
                }
                if ([strongSelf.audioWriterInput isReadyForMoreMediaData]) {
                    @try {
                        [strongSelf.audioWriterInput appendSampleBuffer:sampleBuffer];
                        NSLog(@"[录屏]写入音频数据");
                    } @catch (NSException *exception) {
                        NSLog(@"[录屏]写入音频数据失败");
                    }
                }
            }
        }
    } completionHandler:^(NSError *_Nullable error) {
       
    }];

下面是 AVAssetWriter 和 AVAssetWriterInput 的配置（因为不是专业的多媒体工程师，所以很多参数配置不一定合理，仅供大家参考）

- (void)setupVideoWriter
{
    if (!_videoWriter) {
        NSURL *outputURL = [NSURL fileURLWithPath:self.videoOutputPath];

        NSError *error = nil;
        _videoWriter = [AVAssetWriter assetWriterWithURL:outputURL fileType:AVFileTypeQuickTimeMovie error:&error];
        if (error) {
            NSLog(@"创建Video Writer失败：%@", [error localizedDescription]);
        }
    }
}

- (void)setupVideoWriterInput
{
    if (!_videoWriterInput) {
        CGFloat scale = [UIScreen mainScreen].scale;
        CGSize size = CGSizeMake(CGRectGetWidth([UIScreen mainScreen].bounds) * scale, CGRectGetHeight([UIScreen mainScreen].bounds) * scale);
        NSDictionary *copressionProperties = @{ AVVideoAverageBitRateKey : @(1200 * 1024) };
        _videoWriterInput = [AVAssetWriterInput assetWriterInputWithMediaType:AVMediaTypeVideo
                                                               outputSettings:@{
                                                                   AVVideoCodecKey : AVVideoCodecH264,
                                                                   AVVideoWidthKey : @(size.width),
                                                                   AVVideoHeightKey : @(size.height),
                                                                   AVVideoCompressionPropertiesKey : copressionProperties
                                                               }];
        _videoWriterInput.expectsMediaDataInRealTime = YES;
        if ([self.videoWriter canAddInput:_videoWriterInput]) {
            [self.videoWriter addInput:_videoWriterInput];
        } else {
            NSLog(@"无法添加Video Writer Input");
        }
    }
}

- (void)setupAudioWriterInput
{
    if (!_audioWriterInput) {
        AudioChannelLayout acl;
        bzero(&acl, sizeof(acl));
        acl.mChannelLayoutTag = kAudioChannelLayoutTag_Mono;

        _audioWriterInput = [AVAssetWriterInput assetWriterInputWithMediaType:AVMediaTypeAudio
                                                               outputSettings:@{
                                                                   AVSampleRateKey : @(44100),
                                                                   AVFormatIDKey : @(kAudioFormatAppleLossless),
                                                                   AVEncoderBitDepthHintKey : @(16),
                                                                   AVNumberOfChannelsKey : @(1),
                                                                   AVChannelLayoutKey : [NSData dataWithBytes:&acl length:sizeof(acl)],
                                                               }];
        _audioWriterInput.expectsMediaDataInRealTime = YES;
        if ([self.videoWriter canAddInput:_audioWriterInput]) {
            [self.videoWriter addInput:_audioWriterInput];
        } else {
            NSLog(@"无法添加Video Writer Input");
        }
    }
}