Create a more responsive media app

1:41 - Generate a thumbnail

func thumbnail() async throws -> UIImage {
    let generator = AVAssetImageGenerator(asset: asset)
    generator.requestedTimeToleranceBefore = .zero
    generator.requestedTimeToleranceAfter = CMTime(seconds: 3, preferredTimescale: 600)
    let thumbnail = try await generator.image(at: time).image
    return UIImage(cgImage: thumbnail)
}

2:56 - Generate a series of thumbnails

func timelineThumbnails(for times: [CMTime]) async {
    for await result in generator.images(for: times) {
        switch result {
        case .success(requestedTime: let requestedTime, image: let image, actualTime: _):
            updateThumbnail(for: requestedTime, with: image)
        case .failed(requestedTime: let requestedTime, error: _):
            updateThumbnail(for: requestedTime, with: placeholder)
        }
    }
}

3:49 - Generate a series of thumbnails

func timelineThumbnails(for times: [CMTime]) async {
    for await result in generator.images(for: times) {
        updateThumbnail(for: result.requestedTime, with: (try? result.image) ?? placeholder)
    }
}

4:40 - AVMutableComposition

let composition = AVMutableComposition()
try await composition.insertTimeRange(timeRange, of: asset, at: startTime)

4:57 - AVVideoComposition

let videoComposition = try await AVVideoComposition .videoComposition(withPropertiesOf: asset)

try await videoComposition.isValid(for: asset, timeRange: range, validationDelegate: delegate)

5:33 - Asset inspection

asset.loadValuesAsynchronously(forKeys: ["duration", "tracks"]) {
    guard asset.statusOfValue(forKey: "duration", error: &error) == .loaded else { ... }
    guard asset.statusOfValue(forKey: "tracks", error: &error) == .loaded else { ... }
    myFunction(thatUses: asset.duration, and: asset.tracks)
}

let (duration, tracks) = try await asset.load(.duration, .tracks)
myFunction(thatUses: duration, and: tracks)

7:06 - Synchronously insert track segments into a composition

// videoTrack1: AVAssetTrack, videoTrack2: AVAssetTrack

// Create a composition and add an empty track
let composition = AVMutableComposition()
guard let compositionTrack = composition
    .addMutableTrack(withMediaType: .video,
                     preferredTrackID: 1) else { return }

// Append the first 5 seconds of track 1
try compositionTrack
    .insertTimeRange(firstFiveSeconds,
                     of: videoTrack1, at: .zero)

// Append the first 5 seconds of track 2
try compositionTrack
    .insertTimeRange(firstFiveSeconds,
                     of: videoTrack2, at: fiveSeconds)
myFunction(thatUses: composition.duration,
           and: composition.tracks)