从 ALAsset 获取视频

Question

使用 iOS 4 中可用的新资产库框架，我发现我可以使用 UIImagePickerControllerReferenceURL 获取给定视频的 url。返回的url格式如下：

assets-library://asset/asset.M4V?id=1000000004&ext=M4V

我正在尝试将此视频上传到网站，以便快速验证概念，我正在尝试以下操作

NSData *data = [NSData dataWithContentsOfURL:videourl];
[data writeToFile:tmpfile atomically:NO];

在这种情况下，数据永远不会被初始化。有没有人设法通过新的资产库直接访问 url？感谢您的帮助。

Answer 1

来自 Zoul 的回答 谢谢

Similar Code in Xamarin C#

Xamarin C# 等效项

IntPtr buffer = CFAllocator.Malloc.Allocate(representation.Size);
NSError error;
            nuint buffered = representation.GetBytes(buffer, Convert.ToInt64(0.0),Convert.ToUInt32(representation.Size),out error);

            NSData sourceData = NSData.FromBytesNoCopy(buffer,buffered,true);
            NSFileManager fileManager = NSFileManager.DefaultManager;
            NSFileAttributes attr = NSFileAttributes.FromDictionary(NSDictionary.FromFile(outputPath));
            fileManager.CreateFile(outputPath, sourceData,attr);

Answer 2

这是 Alonzo 答案的 Objective C 解决方案，使用照片框架

  -(NSURL*)createVideoCopyFromReferenceUrl:(NSURL*)inputUrlFromVideoPicker{

        NSURL __block *videoURL;
        PHFetchResult *phAssetFetchResult = [PHAsset fetchAssetsWithALAssetURLs:@[inputUrlFromVideoPicker ] options:nil];
        PHAsset *phAsset = [phAssetFetchResult firstObject];
        dispatch_group_t group = dispatch_group_create();
        dispatch_group_enter(group);

        [[PHImageManager defaultManager] requestAVAssetForVideo:phAsset options:nil resultHandler:^(AVAsset *asset, AVAudioMix *audioMix, NSDictionary *info) {

            if ([asset isKindOfClass:[AVURLAsset class]]) {
                NSURL *url = [(AVURLAsset *)asset URL];
                NSLog(@"Final URL %@",url);
                NSData *videoData = [NSData dataWithContentsOfURL:url];

                // optionally, write the video to the temp directory
                NSString *videoPath = [NSTemporaryDirectory() stringByAppendingPathComponent:[NSString stringWithFormat:@"%f.mp4",[NSDate timeIntervalSinceReferenceDate]]];

                videoURL = [NSURL fileURLWithPath:videoPath];
                BOOL writeResult = [videoData writeToURL:videoURL atomically:true];

                if(writeResult) {
                    NSLog(@"video success");
                }
                else {
                    NSLog(@"video failure");
                }
                 dispatch_group_leave(group);
                // use URL to get file content
            }
        }];
        dispatch_group_wait(group,  DISPATCH_TIME_FOREVER);
        return videoURL;
    }

Answer 3

这是一个干净的快速解决方案，可以将视频作为 NSData 获取。 它使用 Photos 框架，因为 ALAssetLibrary 自 iOS9 起已弃用：

重要

自 iOS 9.0 起，Assets Library 框架已被弃用。相反，请改用 Photos 框架，它在 iOS 8.0 及更高版本中为使用用户的照片库提供了更多功能和更好的性能。有关详细信息，请参阅照片框架参考。

import Photos

func imagePickerController(picker: UIImagePickerController, didFinishPickingMediaWithInfo info: [String : AnyObject]) {
    self.dismissViewControllerAnimated(true, completion: nil)
    
    if let referenceURL = info[UIImagePickerControllerReferenceURL] as? NSURL {
        let fetchResult = PHAsset.fetchAssetsWithALAssetURLs([referenceURL], options: nil)
        if let phAsset = fetchResult.firstObject as? PHAsset {
            PHImageManager.defaultManager().requestAVAssetForVideo(phAsset, options: PHVideoRequestOptions(), resultHandler: { (asset, audioMix, info) -> Void in
                if let asset = asset as? AVURLAsset {
                    let videoData = NSData(contentsOfURL: asset.URL)
                    
                    // optionally, write the video to the temp directory
                    let videoPath = NSTemporaryDirectory() + "tmpMovie.MOV"
                    let videoURL = NSURL(fileURLWithPath: videoPath)
                    let writeResult = videoData?.writeToURL(videoURL, atomically: true)
                    
                    if let writeResult = writeResult where writeResult {
                        print("success")
                    }
                    else {
                        print("failure")
                    }
                }
            })
        }
    }
}

Answer 4

你去...

AVAssetExportSession* m_session=nil;

-(void)export:(ALAsset*)asset withHandler:(void (^)(NSURL* url, NSError* error))handler
{
    ALAssetRepresentation* representation=asset.defaultRepresentation;
    m_session=[AVAssetExportSession exportSessionWithAsset:[AVURLAsset URLAssetWithURL:representation.url options:nil] presetName:AVAssetExportPresetPassthrough];
    m_session.outputFileType=AVFileTypeQuickTimeMovie;
    m_session.outputURL=[NSURL fileURLWithPath:[NSTemporaryDirectory() stringByAppendingPathComponent:[NSString stringWithFormat:@"%f.mov",[NSDate timeIntervalSinceReferenceDate]]]];
    [m_session exportAsynchronouslyWithCompletionHandler:^
     {
         if (m_session.status!=AVAssetExportSessionStatusCompleted)
         {
             NSError* error=m_session.error;
             m_session=nil;
             handler(nil,error);
             return;
         }
         NSURL* url=m_session.outputURL;
         m_session=nil;
         handler(url,nil);
     }];
}

如果你想重新编码电影，你可以使用不同的预设键（例如AVAssetExportPresetMediumQuality）

Answer 5

我在ALAsset 上使用以下类别：

static const NSUInteger BufferSize = 1024*1024;

@implementation ALAsset (Export)

- (BOOL) exportDataToURL: (NSURL*) fileURL error: (NSError**) error
{
    [[NSFileManager defaultManager] createFileAtPath:[fileURL path] contents:nil attributes:nil];
    NSFileHandle *handle = [NSFileHandle fileHandleForWritingToURL:fileURL error:error];
    if (!handle) {
        return NO;
    }

    ALAssetRepresentation *rep = [self defaultRepresentation];
    uint8_t *buffer = calloc(BufferSize, sizeof(*buffer));
    NSUInteger offset = 0, bytesRead = 0;

    do {
        @try {
            bytesRead = [rep getBytes:buffer fromOffset:offset length:BufferSize error:error];
            [handle writeData:[NSData dataWithBytesNoCopy:buffer length:bytesRead freeWhenDone:NO]];
            offset += bytesRead;
        } @catch (NSException *exception) {
            free(buffer);
            return NO;
        }
    } while (bytesRead > 0);

    free(buffer);
    return YES;
}

@end

Answer 6

这不是最好的方法。我正在回答这个问题，以防其他 SO 用户遇到同样的问题。

基本上，我需要能够将视频文件假脱机为 tmp 文件，以便我可以使用 ASIHTTPFormDataRequest 将其上传到网站。可能有一种从资产 url 流式传输到 ASIHTTPFormDataRequest 上传的方式，但我想不通。相反，我编写了以下函数将文件拖放到 tmp 文件中以添加到 ASIHTTPFormDataRequest。

+(NSString*) videoAssetURLToTempFile:(NSURL*)url
{

    NSString * surl = [url absoluteString];
    NSString * ext = [surl substringFromIndex:[surl rangeOfString:@"ext="].location + 4];
    NSTimeInterval ti = [[NSDate date]timeIntervalSinceReferenceDate];
    NSString * filename = [NSString stringWithFormat: @"%f.%@",ti,ext];
    NSString * tmpfile = [NSTemporaryDirectory() stringByAppendingPathComponent:filename];

    ALAssetsLibraryAssetForURLResultBlock resultblock = ^(ALAsset *myasset)
    {

        ALAssetRepresentation * rep = [myasset defaultRepresentation];

        NSUInteger size = [rep size];
        const int bufferSize = 8192;

        NSLog(@"Writing to %@",tmpfile);
        FILE* f = fopen([tmpfile cStringUsingEncoding:1], "wb+");
        if (f == NULL) {
            NSLog(@"Can not create tmp file.");
            return;
        }

        Byte * buffer = (Byte*)malloc(bufferSize);
        int read = 0, offset = 0, written = 0;
        NSError* err;
        if (size != 0) {
            do {
                read = [rep getBytes:buffer
                          fromOffset:offset
                              length:bufferSize 
                               error:&err];
                written = fwrite(buffer, sizeof(char), read, f);
                offset += read;
            } while (read != 0);


        }
        fclose(f);


    };


    ALAssetsLibraryAccessFailureBlock failureblock  = ^(NSError *myerror)
    {
        NSLog(@"Can not get asset - %@",[myerror localizedDescription]);

    };

    if(url)
    {
        ALAssetsLibrary* assetslibrary = [[[ALAssetsLibrary alloc] init] autorelease];
        [assetslibrary assetForURL:url 
                       resultBlock:resultblock
                      failureBlock:failureblock];
    }

    return tmpfile;
}