UIImagePickerController: Strange result of video compression - iphone

Question

In my app, the user can either record a video or select one from his library. Naturally, I use a UIImagePickerController with it's sourceType set to either UIImagePickerControllerSourceTypeCamera or UIImagePickerControllerSourceTypePhotoLibrary.
The videoQuality is set to UIImagePickerControllerQualityTypeMedium in both cases.
Now, I did the following: I took a 15 sec video with my iPhone lying on it's back, so it's pitch-black. When I choose this video from the library, it is about 0.6 MB big. When I shoot the same video from within my app (15 sec, pitch-black), I get a file of over 4 MB.
Can anybody confirm this? I can hardly believe that I'm the first one to notice but then again, there is not much space for me to screw it up here (which I probably did nonetheless). Or does anybody have an explanation/solution for this?
(I'm at iOS 5.1 with an iPhone 4)

Answer 1

have you figured it out?
Now I have the same problem, a video in PhotoLibrary(2 minutes more); When I get it using UIImagePickerController, it's just about 30 Mb; But I get by the asset.defaultRepresentation（use this way(Getting video from ALAsset)）, it reaches about 300Mb; Maybe the UIImagePickerController compressed the data in some way; I need to figure it out, but make no progress.......
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EDIT: UIVideoEditorController can compress video to small size; and you can set the videoQuality just like UIImagePickerController.
maybe like this: when you use UIImagePickerController to chose a video, and set allowsEditing=YES, it will present UIVideoEditorController to compress video, then you get the compressed video in small size.

Answer 2

I've figured it out now. The solution is not to decrease the dimensions, but the bitrate. That is I think what Apple is doing when you select a video from the library.
Check out my answer here: https://stackoverflow.com/a/16035330/884119

Answer 3

Best way to compress the Video.
Here is the code.
-(void)imagePickerController:(UIImagePickerController *)picker didFinishPickingMediaWithInfo:(NSDictionary *)info{
NSString *tempFilePath = [[info objectForKey:UIImagePickerControllerMediaURL] path];
NSData *data = [NSData dataWithContentsOfURL:videoURL];
NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
NSDate *now = [NSDate dateWithTimeIntervalSinceNow:0];
NSString *caldate = [NSString stringWithFormat:#"%#.mov",[now description]];
caldate = [caldate stringByReplacingOccurrencesOfString:#" " withString:#""];
NSString *documentsDirectory = [paths objectAtIndex:0];
NSString *path = [NSString stringWithFormat:#"%#/%#", documentsDirectory,caldate];
NSString *mediaType = [info objectForKey: UIImagePickerControllerMediaType];
NSURL *selectedVideoUrl;
if (CFStringCompare ((__bridge CFStringRef) mediaType, kUTTypeMovie, 0)
== kCFCompareEqualTo) {
tempFilePath = [[info objectForKey:UIImagePickerControllerMediaURL] path];
selectedVideoUrl = [info objectForKey:UIImagePickerControllerMediaURL];
}
NSLog(#"old move %#",path);
NSURL *url = [NSURL fileURLWithPath:tempFilePath];
[data writeToFile:path atomically:YES];
//Delete the original asset
NSArray *paths1 = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
NSString *documentsDirectory1 = [paths1 objectAtIndex:0];
NSString *path1 = [NSString stringWithFormat:#"%#/%#", documentsDirectory1,caldate];
NSURL *url1 = [NSURL fileURLWithPath:path1];
NSLog(#"new move %#",path);
[self convertVideoToLowQuailtyWithInputURL:url outputURL:url1 handler:Nil];
[picker dismissModalViewControllerAnimated: YES];
}
-(void)convertVideoToLowQuailtyWithInputURL:(NSURL*)inputURL
outputURL:(NSURL*)outputURL
handler:(void (^)(AVAssetExportSession*))handler{
AVURLAsset *asset = [AVURLAsset URLAssetWithURL:inputURL options:nil];
AVAssetExportSession *exportSession = [[AVAssetExportSession alloc] initWithAsset:asset presetName:AVAssetExportPresetMediumQuality];
exportSession.outputURL = outputURL;
if ([[UIApplication sharedApplication]canOpenURL:inputURL]){
NSLog(#"open");
}
exportSession.outputFileType = AVFileTypeQuickTimeMovie;
NSLog(#"errrsfseSession %#", exportSession.error);
[exportSession exportAsynchronouslyWithCompletionHandler:^(void)
{
if(exportSession.status != AVAssetExportSessionStatusCompleted){
NSLog(#"exportSession %#", exportSession.error);
}
if (exportSession.status == AVAssetExportSessionStatusCompleted)
{
NSLog(#"doneszdfsadj");
}
}];
}