- (void)Metadata {
AVURLAsset *asset = [AVURLAsset URLAssetWithURL:self.fileURL options:nil];

NSArray *artworks = [AVMetadataItem MetadataItemsFromArray:asset.commonMetadata withKey:AVMetadataCommonKeyArtwork keySpace:AVMetadataKeySpaceCommon];
NSArray *titles = [AVMetadataItem MetadataItemsFromArray:asset.commonMetadata withKey:AVMetadataCommonKeyTitle keySpace:AVMetadataKeySpaceCommon];
NSArray *artists = [AVMetadataItem MetadataItemsFromArray:asset.commonMetadata withKey:AVMetadataCommonKeyArtist keySpace:AVMetadataKeySpaceCommon];
NSArray *albumNames = [AVMetadataItem MetadataItemsFromArray:asset.commonMetadata withKey:AVMetadataCommonKeyAlbumName keySpace:AVMetadataKeySpaceCommon];

AVMetadataItem *artwork = [artworks objectAtIndex:0];
AVMetadataItem *title = [titles objectAtIndex:0];
AVMetadataItem *artist = [artists objectAtIndex:0];
AVMetadataItem *albumName = [albumNames objectAtIndex:0];

if ([artwork.keySpace isEqualToString:AVMetadataKeySpaceID3]) {
    NSDictionary *dictionary = [artwork.value copyWithZone:nil];
    self.currentSongArtwork = [UIImage imageWithData:[dictionary objectForKey:@"data"]];
}
else if ([artwork.keySpace isEqualToString:AVMetadataKeySpaceiTunes]) {
    self.currentSongArtwork = [UIImage imageWithData:[artwork.value copyWithZone:nil]];
}

self.currentSongTitle = [title.value copyWithZone:nil];
self.currentSongArtist = [artist.value copyWithZone:nil];
self.currentSongalbumName = [albumName.value copyWithZone:nil];
self.currentSongDuration = self.audioPlayer.duration;
}

这适用于从m4a文件中获取图稿,但不适用于mp3文件.如果资产指向mp3文件,则艺术品为空.我做错了什么,我该如何解决？

- (void)Metadata {
AVURLAsset *asset = [AVURLAsset URLAssetWithURL:self.fileURL options:nil];

NSArray *titles = [AVMetadataItem MetadataItemsFromArray:asset.commonMetadata withKey:AVMetadataCommonKeyTitle keySpace:AVMetadataKeySpaceCommon];
NSArray *artists = [AVMetadataItem MetadataItemsFromArray:asset.commonMetadata withKey:AVMetadataCommonKeyArtist keySpace:AVMetadataKeySpaceCommon];
NSArray *albumNames = [AVMetadataItem MetadataItemsFromArray:asset.commonMetadata withKey:AVMetadataCommonKeyAlbumName keySpace:AVMetadataKeySpaceCommon];

AVMetadataItem *title = [titles objectAtIndex:0];
AVMetadataItem *artist = [artists objectAtIndex:0];
AVMetadataItem *albumName = [albumNames objectAtIndex:0];


NSArray *keys = [NSArray arrayWithObjects:@"commonMetadata",nil];
[asset loadValuesAsynchronouslyForKeys:keys completionHandler:^{
    NSArray *artworks = [AVMetadataItem MetadataItemsFromArray:asset.commonMetadata
                                                       withKey:AVMetadataCommonKeyArtwork
                                                      keySpace:AVMetadataKeySpaceCommon];

    for (AVMetadataItem *item in artworks) {
        if ([item.keySpace isEqualToString:AVMetadataKeySpaceID3]) {
            NSDictionary *d = [item.value copyWithZone:nil];
            self.currentSongArtwork = [UIImage imageWithData:[d objectForKey:@"data"]];
        } else if ([item.keySpace isEqualToString:AVMetadataKeySpaceiTunes]) {
            self.currentSongArtwork = [UIImage imageWithData:[item.value copyWithZone:nil]];
        }
    }
}];


self.currentSongTitle = [title.value copyWithZone:nil];
self.currentSongArtist = [artist.value copyWithZone:nil];
self.currentSongalbumName = [albumName.value copyWithZone:nil];
self.currentSongDuration = self.audioPlayer.duration;
}

这可能是,但我不知道如何去做这件事.有关设置方向的文档是关于正确设置以便在设备上显示,我已经实现了建议found here.但是,此建议并未解决为非Apple软件(如VLC或Chrome浏览器)正确设置方向的问题. .

任何人都可以提供有关如何在设备上正确设置方向以便正确显示所有查看软件的信息吗？

+(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;

}

谁知道有没有办法知道光的容量？

我知道其中一种方法是使用环境光传感器,但它不鼓励,最终应用程序不允许在市场上

我发现问题非常接近我需要的问题

detecting if iPhone is in a dark room

那个人解释说我可以使用ImageIO框架,读取视频源的每一帧进来的元数据

- (void)captureOutput:(AVCaptureOutput *)captureOutput didOutputSampleBuffer:(CMSampleBufferRef)sampleBuffer fromConnection:(AVCaptureConnection *)connection {
  CFDictionaryRef MetadataDict = CMcopyDictionaryOfAttachments(NULL,sampleBuffer,kCMAttachmentMode_ShouldPropagate);
  NSDictionary *Metadata = [[NSMutableDictionary alloc] initWithDictionary:(__bridge NSDictionary*)MetadataDict];
  CFRelease(MetadataDict);
  NSDictionary *exifMetadata = [[Metadata objectForKey:(Nsstring *)kCGImagePropertyExifDictionary] mutablecopy];
  float brightnessValue = [[exifMetadata objectForKey:(Nsstring *)kCGImagePropertyExifBrightnessValue]  floatValue];
}

但我是iOS的新手,不知道如何在Swift中转换这段代码

提前致谢！

可以使用相机的EXIF数据获得近似光度值(以单位勒克斯为单位).请参考以下链接. Using a camera as a lux meter

这里AVFoundation中captureOutput方法的sampleBuffer值用于从相机帧中提取EXIF数据.

func captureOutput(_ captureOutput: AVCaptureOutput!,didOutputSampleBuffer sampleBuffer: CMSampleBuffer!,from connection: AVCaptureConnection!) {

    //Retrieving EXIF data of camara frame buffer
    let rawMetadata = CMcopyDictionaryOfAttachments(nil,CMAttachmentMode(kCMAttachmentMode_ShouldPropagate))
    let Metadata = CFDictionaryCreateMutablecopy(nil,rawMetadata) as NSMutableDictionary
    let exifData = Metadata.value(forKey: "{Exif}") as? NSMutableDictionary

    let FNumber : Double = exifData?["FNumber"] as! Double
    let ExposureTime : Double = exifData?["ExposureTime"] as! Double
    let ISOSpeedratingsArray = exifData!["ISOSpeedratings"] as? NSArray
    let ISOSpeedratings : Double = ISOSpeedratingsArray![0] as! Double
    let CalibrationConstant : Double = 50 

    //Calculating the luminosity
    let luminosity : Double = (CalibrationConstant * FNumber * FNumber ) / ( ExposureTime * ISOSpeedratings )  

    print(luminosity)}

请注意,CalibrationConstant的值可以根据应用进行校准,如参考文献中所述.