Francesco Scotti Francesco Scotti - 3 months ago 11
Swift Question

How do i export images as video in Swift?

i am making an app in Swift (i have the last xcode update) that has to generate a video from some images.

I got the code from this answer How do I export UIImage array as a movie?

I call the function like this:

let size = CGSize(width: 1280, height: 720)
let pathVideo = NSSearchPathForDirectoriesInDomains(.DocumentDirectory, .UserDomainMask, true)
let percorsoVideo = pathVideo[0]
writeImagesAsMovie(arrayImmagini, videoPath: percorsoVideo+"/prova.mp4", videoSize: size, videoFPS: 1)


"arrayImmagini" is defined literally like this:

var arrayImmagini = [UIImage(imageLiteral: "Frames/turtle/turtle0.jpg"), UIImage(imageLiteral: "Frames/turtle/turtle1.jpg"), ...]


When i try to run the code i get a completely black video and xcode gives me this 2 errors as many times as many images there are in the array:

Sep 5 09:24:15 Prova[1554] <Error>: CGBitmapContextCreate: invalid data bytes/row: should be at least 7680 for 8 integer bits/component, 3 components, kCGImageAlphaPremultipliedFirst.
Sep 5 09:24:15 Prova[1554] <Error>: CGContextDrawImage: invalid context 0x0. If you want to see the backtrace, please set CG_CONTEXT_SHOW_BACKTRACE environmental variable.


Reading the documentation about CGBitmapContextCreate, i tried to call it differently:

func fillPixelBufferFromImage(image: UIImage, pixelBuffer: CVPixelBufferRef) {
CVPixelBufferLockBaseAddress(pixelBuffer, 0)

let pixelData = CVPixelBufferGetBaseAddress(pixelBuffer)
let rgbColorSpace = CGColorSpaceCreateDeviceRGB()

// Create CGBitmapContext
let context = CGBitmapContextCreate(
nil,
Int(image.size.width),
Int(image.size.height),
8,
0,
rgbColorSpace,
CGImageAlphaInfo.PremultipliedFirst.rawValue
)

// Draw image into context
CGContextDrawImage(context, CGRectMake(0, 0, image.size.width, image.size.height), image.CGImage)

CVPixelBufferUnlockBaseAddress(pixelBuffer, 0)
}


Instead of:

func fillPixelBufferFromImage(image: UIImage, pixelBuffer: CVPixelBufferRef) {
CVPixelBufferLockBaseAddress(pixelBuffer, 0)

let pixelData = CVPixelBufferGetBaseAddress(pixelBuffer)
let rgbColorSpace = CGColorSpaceCreateDeviceRGB()

// Create CGBitmapContext
let context = CGBitmapContextCreate(
pixelData,
Int(image.size.width),
Int(image.size.height),
8,
CVPixelBufferGetBytesPerRow(pixelBuffer),
rgbColorSpace,
CGImageAlphaInfo.PremultipliedFirst.rawValue
)

// Draw image into context
CGContextDrawImage(context, CGRectMake(0, 0, image.size.width, image.size.height), image.CGImage)

CVPixelBufferUnlockBaseAddress(pixelBuffer, 0)
}


This made xcode stop giving me errors but i still get a black video.

Please help me, i'm new to app development and even newer to AVFoundation, i don't have any clues about how to solve it by myself.


Thank you!

Answer

After many attempts to make this work i found out what the problem was. You can't give a video size more little than the pictures' size.
Once i did this, everything worked:

let size = CGSize(width: 1920, height: 1280)