How to check Resolution, bitrate of video in iOS

Question

I'm developing a video compression functionally; my ideas are below:

1. Getting resolution and bit-rate of video.
2. Check resolution of video. If it larger 640x480, I will compress this video in half and adjust the bit rate in 1/4 . E.g., if resolution of video is 1920x1080, it will be compressed to 960x540 and 1920x1080 at 4mbps will be compressed to 960x540 at 1mbps.

I have a few questions:

1. How can get resolution and bit-rate of video in iOS?
2. If compress 1920x1080 in half to 960x540, the bit-rate will also adaptively adjust, or do I still need to set the bitrate manually? How can do that?

I tried below code to compress video but I don't know it compressed to which resolution:

- (void)convertVideoToLowQuailtyWithInputURL:(NSURL*)inputURL
                                   outputURL:(NSURL*)outputURL
                                     handler:(void (^)(AVAssetExportSession*))handler
{
    [[NSFileManager defaultManager] removeItemAtURL:outputURL error:nil];
    AVURLAsset *urlAsset = [AVURLAsset URLAssetWithURL:inputURL options:nil];

    AVAssetExportSession *session = [[AVAssetExportSession alloc] initWithAsset: urlAsset presetName:AVAssetExportPresetLowQuality];
    session.outputURL = outputURL;
    session.outputFileType = AVFileTypeQuickTimeMovie;
    [session exportAsynchronouslyWithCompletionHandler:^(void)
     {
         handler(session);

     }];
}

Please give me some advice. Thanks in advance.

Answer 1

To get the resolution of the video use this :-

AVAssetTrack *videoTrack = nil;
AVURLAsset *asset = [AVAsset assetWithURL:[NSURL fileURLWithPath:originalVideo]];
NSArray *videoTracks = [asset tracksWithMediaType:AVMediaTypeVideo];

CMFormatDescriptionRef formatDescription = NULL;
NSArray *formatDescriptions = [videoTrack formatDescriptions];
if ([formatDescriptions count] > 0)
    formatDescription = (CMFormatDescriptionRef)[formatDescriptions objectAtIndex:0];

if ([videoTracks count] > 0)
    videoTrack = [videoTracks objectAtIndex:0];

CGSize trackDimensions = {
    .width = 0.0,
    .height = 0.0,
};
trackDimensions = [videoTrack naturalSize];

int width = trackDimensions.width;
int height = trackDimensions.height;
NSLog(@"Resolution = %d X %d",width ,height);

you can get the frameRate and bitrate as follows:-

float frameRate = [videoTrack nominalFrameRate];
float bps = [videoTrack estimatedDataRate];
NSLog(@"Frame rate == %f",frameRate);
NSLog(@"bps rate == %f",bps);

Answer 2

Video resolution in Swift:

func resolutionForLocalVideo(url:NSURL) -> CGSize?
{
    guard let track = AVAsset(URL: url).tracksWithMediaType(AVMediaTypeVideo).first else { return nil }
    let size = CGSizeApplyAffineTransform(track.naturalSize, track.preferredTransform)
    return CGSize(width: fabs(size.width), height: fabs(size.height))
}

Solutions without preferredTransform do not return correct values for some videos on the latest devices!