iphone - ALAssets 获取视频数据

Question

我正在尝试使用以下代码从 ALAssets 库访问视频数据

        ALAssetRepresentation *rep = [asset defaultRepresentation];
        Byte *buffer = (Byte*)malloc(rep.size);
        NSError *error = nil;
        NSUInteger buffered = [rep getBytes:buffer fromOffset:0.0 length:rep.size error:&error];
        NSData *data = [NSData dataWithBytesNoCopy:buffer length:buffered freeWhenDone:YES];

它适用于小视频和图片，但如果我尝试获取大视频，代码就会崩溃

* Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '* -[NSConcreteData initWithBytes:length:copy:freeWhenDone:bytesAreVM:]: absurd length: 4294967295, maximum size: 2147483648 bytes'

我不知道发生了什么。大家有什么想法吗？

提前致谢!

Answer 1

我找到了解决方案。我猜崩溃可能是由于我们上传大文件时出现的巨大内存峰值，因为我正在缓冲数据。现在我将文件数据读取为 5 MB block ，这解决了崩溃问题。我将我的代码粘贴在下面。

- (NSData *)getDataPartAtOffset:(NSInteger)offset  {
__block NSData *chunkData = nil;
if (fileAsset_){
    static const NSUInteger BufferSize = PART_SIZE; // 5 MB chunk
    ALAssetRepresentation *rep = [fileAsset_ defaultRepresentation];
    uint8_t *buffer = calloc(BufferSize, sizeof(*buffer));
    NSUInteger bytesRead = 0;
    NSError *error = nil;

    @try
    {
        bytesRead = [rep getBytes:buffer fromOffset:offset length:BufferSize error:&error];
        chunkData = [NSData dataWithData:[NSData dataWithBytesNoCopy:buffer length:bytesRead freeWhenDone:NO]];
    }
    @catch (NSException *exception)
    {
        free(buffer);
        chunkData = nil;
        // Handle the exception here...
    }

    free(buffer);
} else {
    NSLog(@"failed to retrive Asset");
}
return chunkData;

}

我将这个函数称为

   int offset = 0; // offset that keep tracks of chunk data

  do {
        @autoreleasepool {
            NSData *chunkData = [self getDataPartAtOffset:offset];;

            if (!chunkData || ![chunkData length]) { // finished reading data
                break;
            }

            // do your stuff here

            offset +=[chunkData length];
        }
    } while (1);