场景：相册视频导出，导出出现下面错误：

Error Domain=AVFoundationErrorDomain Code=-11800 "这项操作无法完成" UserInfo={NSLocalizedFailureReason=发生未知错误（-12769）, NSLocalizedDescription=这项操作无法完成, NSUnderlyingError=0x281c65ec0 {Error Domain=NSOSStatusErrorDomain Code=-12769 "(null)"}}

出现此错误，
1）、首先检查传入的输出路径是否有问题；
2）、presetName是否支持
3）、若其他配置参数都正确，还考虑是否为该视频编码有问题，可能是生成该视频时编码器出现了问题，可以通过下面方式让AVAssetExportSession重新编码来解决

AVMutableComposition *mainComposition = [[AVMutableComposition alloc] init];
AVMutableCompositionTrack *compositionVideoTrack = [mainComposition addMutableTrackWithMediaType:AVMediaTypeVideo
                                                                                            preferredTrackID:kCMPersistentTrackID_Invalid];
            
int timeScale = 100000;
Float64 seconds = CMTimeGetSeconds([avAsset duration]) - 0.001;
NSUInteger videoDurationI = (NSUInteger) (seconds * timeScale);
CMTime videoDuration = CMTimeMake(videoDurationI, timeScale);
CMTimeRange videoTimeRange = CMTimeRangeMake(kCMTimeZero, videoDuration);
            
NSArray<AVAssetTrack *> *videoTracks = [avAsset tracksWithMediaType:AVMediaTypeVideo];
AVAssetTrack *videoTrack = [videoTracks objectAtIndex:0];

[compositionVideoTrack insertTimeRange:videoTimeRange
                                           ofTrack:videoTrack
                                            atTime:kCMTimeZero
                                             error:nil];
            
AVAssetExportSession *session = [[AVAssetExportSession alloc] initWithAsset:mainComposition presetName:presetName];