iPhone:Programmatically compressing recorded video to share?

If you want to compress the video for remote sharing and keep the original quality for local storage on the iPhone, you should look into AVAssetExportSession or AVAssetWriter.

Also read up on how iOS manages Assets.

- (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];
    }];
}

- (void)imagePickerController:(UIImagePickerController *)picker didFinishPickingMediaWithInfo:(NSDictionary *)info

{   
    NSURL *videoURL = [info objectForKey:UIImagePickerControllerMediaURL];
    NSURL *outputURL = [NSURL fileURLWithPath:@"/Users/josh/Desktop/output.mov"];
    [self convertVideoToLowQuailtyWithInputURL:videoURL outputURL:outputURL handler:^(AVAssetExportSession *exportSession)
     {
         if (exportSession.status == AVAssetExportSessionStatusCompleted)
         {
             printf("completed\n");
         }
         else
         {
             printf("error\n");

         }
     }];

}

I guess the video is already compressed by the h264 codec. But you can try to use AVFoundation to capture the video files from camera. But I suspect you'll end up with the same file sizes.

Here is some statistics for the 10 seconds video file recorded on the iPhone 4 with different quality pressets.

high (1280х720) = ~14MB = ~11Mbit/s
640 (640х480) = ~4MB = ~3.2Mbit/s
medium (360х480) = ~1MB = ~820Kbit/s
low (144х192) = ~208KB = ~170Kbit/s

pickerController.videoQuality = UIImagePickerControllerQualityTypeMedium;

These are all the values you can pick from.

UIImagePickerControllerQualityTypeHigh    = 0,
UIImagePickerControllerQualityType640x480 = 3,
UIImagePickerControllerQualityTypeMedium  = 1,  // default value
UIImagePickerControllerQualityTypeLow     = 2