减少视频的帧速率，以使GIF迅速感觉到

Question

我一直在试图将视频的帧率降低到每秒10或15帧。4/5年前有一些与OBJC相关的问题。我在Swift中找不到任何东西。

这是我在操场上工作的东西：

import Cocoa
import AVKit

var assetWriter:AVAssetWriter?
var assetReader:AVAssetReader?
let bitrate:NSNumber = NSNumber(value:8000000)
func compressFile(urlToCompress: URL, outputURL: URL, completion:@escaping (URL)->Void){
    var videoFinished = false
    let asset = AVAsset(url: urlToCompress);
    do{
        assetReader = try AVAssetReader(asset: asset)
    } catch{
        assetReader = nil
    }
    guard let reader = assetReader else{
        fatalError("Could not initalize asset reader probably failed its try catch")
    }
    let videoTrack = asset.tracks(withMediaType: AVMediaType.video).first!
    let videoReaderSettings: [String:Any] =  [(kCVPixelBufferPixelFormatTypeKey as String?)!:kCVPixelFormatType_32ARGB ]
    let videoSettings:[String:Any] = [
        AVVideoCompressionPropertiesKey: [AVVideoAverageBitRateKey:bitrate],
        AVVideoCodecKey: AVVideoCodecType.h264,
        AVVideoHeightKey: videoTrack.naturalSize.height,
        AVVideoWidthKey: videoTrack.naturalSize.width
    ]
    let assetReaderVideoOutput = AVAssetReaderTrackOutput(track: videoTrack, outputSettings: videoReaderSettings)
    if reader.canAdd(assetReaderVideoOutput){
        reader.add(assetReaderVideoOutput)
    }else{
        fatalError("Couldn't add video output reader")
    }
    let videoInput = AVAssetWriterInput(mediaType: AVMediaType.video, outputSettings: videoSettings)
    videoInput.transform = videoTrack.preferredTransform
    let videoInputQueue = DispatchQueue(label: "videoQueue")
    do{
        assetWriter = try AVAssetWriter(outputURL: outputURL, fileType: AVFileType.mov)
        assetWriter?.movieTimeScale = 1
    }catch{
        assetWriter = nil
    }
    guard let writer = assetWriter else{
        fatalError("assetWriter was nil")
    }
    writer.shouldOptimizeForNetworkUse = true
    writer.add(videoInput)

    writer.startWriting()
    reader.startReading()
    writer.startSession(atSourceTime: CMTime.zero)

    let closeWriter:()->Void = {
        // if (audioFinished && videoFinished){
        if (videoFinished){
            assetWriter?.finishWriting(completionHandler: {
                checkFileSize(sizeUrl: (assetWriter?.outputURL)!, message: "The file size of the compressed file is: ")
                completion((assetWriter?.outputURL)!)
            })
            assetReader?.cancelReading()
        }
    }
    videoInput.requestMediaDataWhenReady(on: videoInputQueue) {
        while(videoInput.isReadyForMoreMediaData){
            let sample = assetReaderVideoOutput.copyNextSampleBuffer()
            if (sample != nil){
                videoInput.append(sample!)
            }else{
                videoInput.markAsFinished()
                DispatchQueue.main.async {
                    videoFinished = true
                    closeWriter()
                }
                break;
            }
        }
    }

}
func checkFileSize(sizeUrl: URL, message:String){
    let data = NSData(contentsOf: sizeUrl)!
    print(message, (Double(data.length) / 1048576.0), " mb")
}

compressFile(urlToCompress: URL(fileURLWithPath: "/Users/koraybirand/Desktop/video.mp4"), outputURL: URL(fileURLWithPath: "/Users/koraybirand/Desktop/video5.mp4")) { (URL) in
}

Answer 1

尝试在视频设置中添加 AVVideoAverageNonDroppableFrameRateKey

Answer 2

刚刚使用的nextLevelsessionExporter ...指出它仅适用于iOS，但也适用于Mac OS X ...仅修改：

internal func createVideoComposition()
.......
videoComposition.frameDuration = CMTimeMake(value: 1, timescale: Int32(frameRate))

用自己所需的值