- (void)fixVideoDirection:(AVURLAsset *)asset resultBlcok:(void (^)(NSURL *outputURL))resultBlock
{
    
    NSString *videoName = [NSString stringWithFormat:@"%@.mp4",[[NSDate date] stringWithFormat:@"YYYY-MM-dd HH:mm:ss"]];
    NSString *outputURL = [[FileTools createDirectoryInDocumentDirectory:@"/Videos"] stringByAppendingPathComponent:videoName];

    AVMutableComposition *composition = [AVMutableComposition composition];
    
    // 獲取音頻軌道
    AVAssetTrack *audioTrack = [asset tracksWithMediaType:AVMediaTypeAudio].firstObject;
    // 插入音頻軌道
    AVMutableCompositionTrack *audioCompositionTrack = [composition addMutableTrackWithMediaType:AVMediaTypeAudio preferredTrackID:kCMPersistentTrackID_Invalid];
    [audioCompositionTrack insertTimeRange:CMTimeRangeMake(kCMTimeZero, asset.duration) ofTrack:audioTrack atTime:kCMTimeZero error:nil];
    
    // 獲取視頻軌道
    AVAssetTrack *videoTrack = [asset tracksWithMediaType:AVMediaTypeVideo].firstObject;
    // 插入視頻軌道
    AVMutableCompositionTrack *videoCompositionTrack = [composition addMutableTrackWithMediaType:AVMediaTypeVideo preferredTrackID:kCMPersistentTrackID_Invalid];
    [videoCompositionTrack insertTimeRange:CMTimeRangeMake(kCMTimeZero, asset.duration) ofTrack:videoTrack atTime:kCMTimeZero error:nil];
    
    // 獲取視頻修正方向（默認(rèn)為攝像頭方向）
    CGAffineTransform t = videoTrack.preferredTransform;
    CGAffineTransform transform = CGAffineTransformIdentity;
    CGSize renderSize = CGSizeMake(videoTrack.naturalSize.width, videoTrack.naturalSize.height);
    
    if(t.a == 1.0 && t.b == 0 && t.c == 0 && t.d == 1.0) { // LandscapeRight, 0度
       //不需要作處理
        NSLog(@"視頻沒有被旋轉(zhuǎn)");
        
   } else if (t.a == 0 && t.b == 1.0 && t.c == -1.0 && t.d == 0){ //90度
       
        transform = CGAffineTransformTranslate(transform, videoTrack.naturalSize.height, 0);
        transform = CGAffineTransformRotate(transform, M_PI_2*1);
        renderSize = CGSizeMake(videoTrack.naturalSize.height, videoTrack.naturalSize.width);
        NSLog(@"視頻被旋轉(zhuǎn)了90度");
       
    } else if (t.a == -1.0 && t.b == 0 && t.c == 0 && t.d == -1.0) { //180度
        
        transform = CGAffineTransformTranslate(transform, videoTrack.naturalSize.width, videoTrack.naturalSize.height);
        transform = CGAffineTransformRotate(transform, M_PI_2*2);
        renderSize = CGSizeMake(videoTrack.naturalSize.width, videoTrack.naturalSize.height);
        NSLog(@"視頻被旋轉(zhuǎn)了180度");

    } else if(t.a == 0 && t.b == -1.0 && t.c == 1.0 && t.d == 0) { //270度
        
        transform = CGAffineTransformTranslate(transform, 0, videoTrack.naturalSize.width);
        transform = CGAffineTransformRotate(transform, M_PI_2*3);
        renderSize = CGSizeMake(videoTrack.naturalSize.height, videoTrack.naturalSize.width);
        NSLog(@"視頻被旋轉(zhuǎn)了270度");
    }
    
    AVMutableVideoCompositionLayerInstruction *layerInstruciton = [AVMutableVideoCompositionLayerInstruction videoCompositionLayerInstructionWithAssetTrack:videoCompositionTrack];
    [layerInstruciton setTransform:transform atTime:kCMTimeZero]; //旋轉(zhuǎn)
    
    AVMutableVideoCompositionInstruction *compositionInstruction = [AVMutableVideoCompositionInstruction videoCompositionInstruction];
    compositionInstruction.timeRange = CMTimeRangeMake(kCMTimeZero, asset.duration);
    compositionInstruction.layerInstructions = @[layerInstruciton];
    
    AVMutableVideoComposition *videoComposition = [AVMutableVideoComposition videoComposition];
    videoComposition.instructions = @[compositionInstruction];
    videoComposition.frameDuration = CMTimeMakeWithSeconds( 1 / videoTrack.nominalFrameRate, 600);;
    videoComposition.renderScale = 1;
    videoComposition.renderSize = renderSize;
    
    // 創(chuàng)建視頻導(dǎo)出會話
    AVAssetExportSession *session = [[AVAssetExportSession alloc] initWithAsset:composition presetName:AVAssetExportPresetHighestQuality];
    session.outputFileType = AVFileTypeMPEG4;
    session.outputURL = [NSURL fileURLWithPath:outputURL];
    session.shouldOptimizeForNetworkUse = YES;
    session.videoComposition = videoComposition;
       
    // 開始導(dǎo)出
    [session exportAsynchronouslyWithCompletionHandler:^{
        if (session.status == AVAssetExportSessionStatusCompleted) {
            resultBlock([NSURL fileURLWithPath:outputURL]);
        } else {
            NSLog(@"視頻導(dǎo)出失敗");
        }
    }];
}

原文地址

iOS 視頻方向修正