Read the asset from the Library and get decompres

In the above post the size of the asset file is too big so here is another way to decompress the file
This is also taken from the stack over flow,

http://stackoverflow.com/questions/5687341/iphoneprogrammatically-compressing-recorded-video-to-share

- (void)convertVideoToLowQuailtyWithInputURL:(NSURL*)inputURL 

                                   outputURL:(NSURL*)outputURL 

                                     handler:(void (^)(AVAssetExportSession*))handler

{

    [[NSFileManager defaultManager] removeItemAtURL:outputURL error:nil];

    AVURLAsset *asset = [AVURLAsset URLAssetWithURL:inputURL options:nil];

    AVAssetExportSession *exportSession = [[AVAssetExportSession alloc] initWithAsset:asset presetName:AVAssetExportPresetLowQuality];

    exportSession.outputURL = outputURL;

    exportSession.outputFileType = AVFileTypeQuickTimeMovie;

    [exportSession exportAsynchronouslyWithCompletionHandler:^(void) 

     {

         handler(exportSession);

         [exportSession release];

     }];

}

Export movie/image asset file into the disk

This is taken from the stack overflow and slightly modified 

- (BOOL) exportDataToURL: (NSString*) filePath error: (NSError**) error andAsset:(ALAsset*)asset

{

    NSError **errorInternal = nil;

    [[NSFileManager defaultManager] createFileAtPath:filePath contents:nil attributes:nil];

    NSFileHandle *handle = [NSFileHandle fileHandleForWritingAtPath:filePath];

    if (!handle) {

        return NO;

    }

    

    static const NSUInteger BufferSize = 1024*1024;

    ALAssetRepresentation *rep = [asset 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;

}

Read the file from assets-library and write into ur custom file

Although u can see many same solutions available same as given below...

This method take the Asset and fileName to create that file into the tempdirectory. 

It returns the path of the tempdirectory/file where it stores the 

This is the same as reading a file from the Assets library (Photo library). 

-(NSString*) writeVideoFileIntoTemp:(NSString*)fileName andAsset:(ALAsset*)asset

{

    NSString * tmpfile = [NSTemporaryDirectory() stringByAppendingPathComponent:fileName];

        

        ALAssetRepresentation * rep = [asset defaultRepresentation];

        

        NSUInteger size = [rep size];

        const int bufferSize = 1024*1024; // or use 8192 size as read from other posts 

        

        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);

    return tmpfile;

}