jamesmacwhite

Converting mkv to mp4 with ffmpeg

Essentially just copy the existing video and audio stream as is into a new container, no funny business!

The easiest way to "convert" MKV to MP4, is to copy the existing video and audio streams and place them into a new container. This avoids any encoding task and hence no quality will be lost, it is also a fairly quick process and requires very little CPU power. The main factor is disk read/write speed.

With ffmpeg this can be achieved with -c copy. Older examples may use -vcodec copy -acodec copy which does the same thing.

These examples assume ffmpeg is in your PATH. If not just substitute with the full path to your ffmpeg binary.

Single file conversion example

benbahrenburg

func UIImageToDataIO(image: UIImage, compressionRatio: CGFloat, orientation: Int = 1) -> Data? {
    return autoreleasepool(invoking: { () -> Data in
        let data = NSMutableData()
        let options: NSDictionary = [
            kCGImagePropertyOrientation: orientation,
            kCGImagePropertyHasAlpha: true,
            kCGImageDestinationLossyCompressionQuality: compressionRatio
        ]
        
        let imageDestinationRef = CGImageDestinationCreateWithData(data as CFMutableData, kUTTypeJPEG, 1, nil)!

benbahrenburg

import UIKit
import ImageIO
import MobileCoreServices
import PlaygroundSupport

PlaygroundPage.current.needsIndefiniteExecution = true

func report_memory() -> UInt64 {
    var taskInfo = mach_task_basic_info()
    var count = mach_msg_type_number_t(MemoryLayout<mach_task_basic_info>.size)/4

skyebook

public func CVPixelBufferGetPixelFormatName(pixelBuffer: CVPixelBuffer) -> String {
    let p = CVPixelBufferGetPixelFormatType(pixelBuffer)
    switch p {
    case kCVPixelFormatType_1Monochrome:                   return "kCVPixelFormatType_1Monochrome"
    case kCVPixelFormatType_2Indexed:                      return "kCVPixelFormatType_2Indexed"
    case kCVPixelFormatType_4Indexed:                      return "kCVPixelFormatType_4Indexed"
    case kCVPixelFormatType_8Indexed:                      return "kCVPixelFormatType_8Indexed"
    case kCVPixelFormatType_1IndexedGray_WhiteIsZero:      return "kCVPixelFormatType_1IndexedGray_WhiteIsZero"
    case kCVPixelFormatType_2IndexedGray_WhiteIsZero:      return "kCVPixelFormatType_2IndexedGray_WhiteIsZero"
    case kCVPixelFormatType_4IndexedGray_WhiteIsZero:      return "kCVPixelFormatType_4IndexedGray_WhiteIsZero"

BrianLitwin

import CoreData

let context = NSManagedObjectContext(concurrencyType: .mainQueueConcurrencyType)

class Book: NSManagedObject {
    var title: String?
    var author: Author?
    var date: Date?
}

tclementdev

libdispatch efficiency tips

The libdispatch is one of the most misused API due to the way it was presented to us when it was introduced and for many years after that, and due to the confusing documentation and API. This page is a compilation of important things to know if you're going to use this library. Many references are available at the end of this document pointing to comments from Apple's very own libdispatch maintainer (Pierre Habouzit).

My take-aways are:

• You should create very few, long-lived, well-defined queues. These queues should be seen as execution contexts in your program (gui, background work, ...) that benefit from executing in parallel. An important thing to note is that if these queues are all active at once, you will get as many threads running. In most apps, you probably do not need to create more than 3 or 4 queues.

• Go serial first, and as you find performance bottle necks, measure why, and if concurrency helps, apply with care, always validating under system pressure. Reuse

lanserxt

final class LoopedVideoPlayerView: UIView {
    
    fileprivate var videoURL: URL?
    fileprivate var queuePlayer: AVQueuePlayer?
    fileprivate var playerLayer: AVPlayerLayer?
    fileprivate var playbackLooper: AVPlayerLooper?
    
    func prepareVideo(_ videoURL: URL) {
        
        let playerItem = AVPlayerItem(url: videoURL)

aainaj

import Foundation
import PlaygroundSupport

PlaygroundPage.current.needsIndefiniteExecution = true

var value: Int = 2

let concurrentQueue = DispatchQueue(label: "queue", attributes: .concurrent)

concurrentQueue.async(flags: .barrier) {

funmia

Resources

• https://fluffy.es/closure-overview/
• https://grokswift.com/completion-handler-faqs/
• http://alisoftware.github.io/swift/closures/2016/07/25/closure-capture-1/
• https://www.andrewcbancroft.com/2017/04/26/what-in-the-world-is-an-escaping-closure-in-swift/
• https://medium.com/@stremsdoerfer/understanding-memory-leaks-in-closures-48207214cba
• https://blog.bobthedeveloper.io/swift-capture-list-in-closures-e28282c71b95

funmia

struct Todo: Decodable {
    let userId: Int
    let id: Int
    let title: String
    let completed: Bool
}

func getToDoItems(completionHandler: @escaping ([Todo]) -> Void) {