I would make reduced size video, maybe 50 pixel across and 75 pixels for length. Those are the physical dimension.
How do you set that? in the videosettings? I think
You need to set video codec parameters:
NSDictionary *videoCleanApertureSettings = [NSDictionary dictionaryWithObjectsAndKeys:
[NSNumber numberWithInt:320], AVVideoCleanApertureWidthKey,
[NSNumber numberWithInt:480], AVVideoCleanApertureHeightKey,
[NSNumber numberWithInt:10], AVVideoCleanApertureHorizontalOffsetKey,
[NSNumber numberWithInt:10], AVVideoCleanApertureVerticalOffsetKey,
nil];
NSDictionary *videoAspectRatioSettings = [NSDictionary dictionaryWithObjectsAndKeys:
[NSNumber numberWithInt:3], AVVideoPixelAspectRatioHorizontalSpacingKey,
[NSNumber numberWithInt:3],AVVideoPixelAspectRatioVerticalSpacingKey,
nil];
NSDictionary *codecSettings = [NSDictionary dictionaryWithObjectsAndKeys:
[NSNumber numberWithInt:960000], AVVideoAverageBitRateKey,
[NSNumber numberWithInt:1],AVVideoMaxKeyFrameIntervalKey,
videoCleanApertureSettings, AVVideoCleanApertureKey,
//videoAspectRatioSettings, AVVideoPixelAspectRatioKey,
//AVVideoProfileLevelH264Main30, AVVideoProfileLevelKey,
nil];
NSString *targetDevice = [[UIDevice currentDevice] model];
NSDictionary *videoSettings = [NSDictionary dictionaryWithObjectsAndKeys:
AVVideoCodecH264, AVVideoCodecKey,
codecSettings,AVVideoCompressionPropertiesKey,
[NSNumber numberWithInt:320], AVVideoWidthKey,
[NSNumber numberWithInt:480], AVVideoHeightKey,
nil];
You need a PhD to work with AVAssetWriter - it's non-trivial: https://developer.apple.com/library/mac/documentation/AudioVideo/Conceptual/AVFoundationPG/Articles/05_Export.html#//apple_ref/doc/uid/TP40010188-CH9-SW1
There's an amazing library for doing exactly what you want which is just an AVAssetExportSession drop-in replacement with more crucial features like changing the bit rate: https://github.com/rs/SDAVAssetExportSession
Here's how to use it:
-(void)imagePickerController:(UIImagePickerController *)picker didFinishPickingMediaWithInfo:(NSDictionary *)info
{
SDAVAssetExportSession *encoder = [SDAVAssetExportSession.alloc initWithAsset:[AVAsset assetWithURL:[info objectForKey:UIImagePickerControllerMediaURL]]];
NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
NSString *documentsDirectory = [paths objectAtIndex:0];
self.myPathDocs = [documentsDirectory stringByAppendingPathComponent:
[NSString stringWithFormat:@"lowerBitRate-%d.mov",arc4random() % 1000]];
NSURL *url = [NSURL fileURLWithPath:self.myPathDocs];
encoder.outputURL=url;
encoder.outputFileType = AVFileTypeMPEG4;
encoder.shouldOptimizeForNetworkUse = YES;
encoder.videoSettings = @
{
AVVideoCodecKey: AVVideoCodecH264,
AVVideoCompressionPropertiesKey: @
{
AVVideoAverageBitRateKey: @2300000,
AVVideoProfileLevelKey: AVVideoProfileLevelH264High40,
},
};
encoder.audioSettings = @
{
AVFormatIDKey: @(kAudioFormatMPEG4AAC),
AVNumberOfChannelsKey: @2,
AVSampleRateKey: @44100,
AVEncoderBitRateKey: @128000,
};
[encoder exportAsynchronouslyWithCompletionHandler:^
{
int status = encoder.status;
if (status == AVAssetExportSessionStatusCompleted)
{
AVAssetTrack *videoTrack = nil;
AVURLAsset *asset = [AVAsset assetWithURL:encoder.outputURL];
NSArray *videoTracks = [asset tracksWithMediaType:AVMediaTypeVideo];
videoTrack = [videoTracks objectAtIndex:0];
float frameRate = [videoTrack nominalFrameRate];
float bps = [videoTrack estimatedDataRate];
NSLog(@"Frame rate == %f",frameRate);
NSLog(@"bps rate == %f",bps/(1024.0 * 1024.0));
NSLog(@"Video export succeeded");
// encoder.outputURL <- this is what you want!!
}
else if (status == AVAssetExportSessionStatusCancelled)
{
NSLog(@"Video export cancelled");
}
else
{
NSLog(@"Video export failed with error: %@ (%d)", encoder.error.localizedDescription, encoder.error.code);
}
}];
}