iOS AVFoundation : Setting Orientation of Video

Question

我一直在努力解决在 iOS 设备上捕获期间和之后控制视频方向的问题。感谢 Apple 之前的回答和文档，我已经能够弄明白了。但是，现在我想将一些视频推送到网站，但遇到了一些特殊问题。我特别概述了这个问题 in this question , 和 the proposed solution事实证明需要在视频编码期间设置方向选项。

可能是这样，但我不知道该怎么做。关于设置方向的文档是关于正确设置它以在设备上显示的，我已经实现了建议 found here.但是，此建议并未解决为非 Apple 软件(例如 VLC 或 Chrome 浏览器)正确设置方向的问题。

谁能深入了解如何在设备上正确设置方向，使其在所有查看软件中都能正确显示？

Answer 1

最后，根据@Aaron Vegh 和@Prince 的回答，我得出了我的解决方案://转换视频

+(void)convertMOVToMp4:(NSString *)movFilePath completion:(void (^)(NSString *mp4FilePath))block{


AVURLAsset * videoAsset = [[AVURLAsset alloc]initWithURL:[NSURL fileURLWithPath:movFilePath]  options:nil];

AVAssetTrack *sourceAudioTrack = [[videoAsset tracksWithMediaType:AVMediaTypeAudio] objectAtIndex:0];

AVMutableComposition* composition = [AVMutableComposition composition];


AVMutableCompositionTrack *compositionAudioTrack = [composition addMutableTrackWithMediaType:AVMediaTypeAudio
                                                                            preferredTrackID:kCMPersistentTrackID_Invalid];
[compositionAudioTrack insertTimeRange:CMTimeRangeMake(kCMTimeZero, videoAsset.duration)
                               ofTrack:sourceAudioTrack
                                atTime:kCMTimeZero error:nil];




AVAssetExportSession * assetExport = [[AVAssetExportSession alloc] initWithAsset:composition
                                                                      presetName:AVAssetExportPresetMediumQuality];


NSString *exportPath =  [movFilePath stringByReplacingOccurrencesOfString:@".MOV" withString:@".mp4"];


NSURL * exportUrl = [NSURL fileURLWithPath:exportPath];


assetExport.outputFileType = AVFileTypeMPEG4;
assetExport.outputURL = exportUrl;
assetExport.shouldOptimizeForNetworkUse = YES;
assetExport.videoComposition = [self getVideoComposition:videoAsset composition:composition];

[assetExport exportAsynchronouslyWithCompletionHandler:
 ^(void ) {
     switch (assetExport.status)
     {
         case AVAssetExportSessionStatusCompleted:
             //                export complete
                    if (block) {
                         block(exportPath);
                }
             break;
         case AVAssetExportSessionStatusFailed:
             block(nil);
             break;
         case AVAssetExportSessionStatusCancelled:
            block(nil);
             break;
     }
 }];
}

//获取当前方向

  +(AVMutableVideoComposition *) getVideoComposition:(AVAsset *)asset composition:( AVMutableComposition*)composition{
    BOOL isPortrait_ = [self isVideoPortrait:asset];


    AVMutableCompositionTrack *compositionVideoTrack = [composition addMutableTrackWithMediaType:AVMediaTypeVideo preferredTrackID:kCMPersistentTrackID_Invalid];


    AVAssetTrack *videoTrack = [[asset tracksWithMediaType:AVMediaTypeVideo] objectAtIndex:0];
    [compositionVideoTrack insertTimeRange:CMTimeRangeMake(kCMTimeZero, asset.duration) ofTrack:videoTrack atTime:kCMTimeZero error:nil];

    AVMutableVideoCompositionLayerInstruction *layerInst = [AVMutableVideoCompositionLayerInstruction videoCompositionLayerInstructionWithAssetTrack:compositionVideoTrack];

    CGAffineTransform transform = videoTrack.preferredTransform;
    [layerInst setTransform:transform atTime:kCMTimeZero];


    AVMutableVideoCompositionInstruction *inst = [AVMutableVideoCompositionInstruction videoCompositionInstruction];
    inst.timeRange = CMTimeRangeMake(kCMTimeZero, asset.duration);
    inst.layerInstructions = [NSArray arrayWithObject:layerInst];


    AVMutableVideoComposition *videoComposition = [AVMutableVideoComposition videoComposition];
    videoComposition.instructions = [NSArray arrayWithObject:inst];

    CGSize videoSize = videoTrack.naturalSize;
    if(isPortrait_) {
        NSLog(@"video is portrait ");
        videoSize = CGSizeMake(videoSize.height, videoSize.width);
    }
    videoComposition.renderSize = videoSize;
    videoComposition.frameDuration = CMTimeMake(1,30);
    videoComposition.renderScale = 1.0;
    return videoComposition;
   }

//获取视频

+(BOOL) isVideoPortrait:(AVAsset *)asset{
BOOL isPortrait = FALSE;
NSArray *tracks = [asset tracksWithMediaType:AVMediaTypeVideo];
if([tracks    count] > 0) {
    AVAssetTrack *videoTrack = [tracks objectAtIndex:0];

    CGAffineTransform t = videoTrack.preferredTransform;
    // Portrait
    if(t.a == 0 && t.b == 1.0 && t.c == -1.0 && t.d == 0)
    {
        isPortrait = YES;
    }
    // PortraitUpsideDown
    if(t.a == 0 && t.b == -1.0 && t.c == 1.0 && t.d == 0)  {

        isPortrait = YES;
    }
    // LandscapeRight
    if(t.a == 1.0 && t.b == 0 && t.c == 0 && t.d == 1.0)
    {
        isPortrait = FALSE;
    }
    // LandscapeLeft
    if(t.a == -1.0 && t.b == 0 && t.c == 0 && t.d == -1.0)
    {
        isPortrait = FALSE;
    }
}
return isPortrait;