Add a basic exporter

This doesn't have a great API yet and hasn't been tested so it may not
even work.

SJSAssetExportSession.xcodeproj/project.pbxproj

@@ -7,10 +7,12 @@
 	objects = {
 
 /* Begin PBXBuildFile section */
+		7B7AE3092C36615700DB7391 /* SampleWriter.swift in Sources */ = {isa = PBXBuildFile; fileRef = 7B7AE3082C36615700DB7391 /* SampleWriter.swift */; };
 		7B9BC00E2C305D2C00C160C2 /* SJSAssetExportSession.docc in Sources */ = {isa = PBXBuildFile; fileRef = 7B9BC00D2C305D2C00C160C2 /* SJSAssetExportSession.docc */; };
 		7B9BC0142C305D2C00C160C2 /* SJSAssetExportSession.framework in Frameworks */ = {isa = PBXBuildFile; fileRef = 7B9BC0092C305D2C00C160C2 /* SJSAssetExportSession.framework */; };
 		7B9BC0192C305D2C00C160C2 /* SJSAssetExportSessionTests.swift in Sources */ = {isa = PBXBuildFile; fileRef = 7B9BC0182C305D2C00C160C2 /* SJSAssetExportSessionTests.swift */; };
 		7B9BC01A2C305D2C00C160C2 /* SJSAssetExportSession.h in Headers */ = {isa = PBXBuildFile; fileRef = 7B9BC00C2C305D2C00C160C2 /* SJSAssetExportSession.h */; settings = {ATTRIBUTES = (Public, ); }; };
+		7B9BC0282C30612C00C160C2 /* ExportSession.swift in Sources */ = {isa = PBXBuildFile; fileRef = 7B9BC0272C30612C00C160C2 /* ExportSession.swift */; };
 /* End PBXBuildFile section */
 
 /* Begin PBXContainerItemProxy section */
@@ -24,11 +26,13 @@
 /* End PBXContainerItemProxy section */
 
 /* Begin PBXFileReference section */
+		7B7AE3082C36615700DB7391 /* SampleWriter.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = SampleWriter.swift; sourceTree = "<group>"; };
 		7B9BC0092C305D2C00C160C2 /* SJSAssetExportSession.framework */ = {isa = PBXFileReference; explicitFileType = wrapper.framework; includeInIndex = 0; path = SJSAssetExportSession.framework; sourceTree = BUILT_PRODUCTS_DIR; };
 		7B9BC00C2C305D2C00C160C2 /* SJSAssetExportSession.h */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.c.h; path = SJSAssetExportSession.h; sourceTree = "<group>"; };
 		7B9BC00D2C305D2C00C160C2 /* SJSAssetExportSession.docc */ = {isa = PBXFileReference; lastKnownFileType = folder.documentationcatalog; path = SJSAssetExportSession.docc; sourceTree = "<group>"; };
 		7B9BC0132C305D2C00C160C2 /* SJSAssetExportSessionTests.xctest */ = {isa = PBXFileReference; explicitFileType = wrapper.cfbundle; includeInIndex = 0; path = SJSAssetExportSessionTests.xctest; sourceTree = BUILT_PRODUCTS_DIR; };
 		7B9BC0182C305D2C00C160C2 /* SJSAssetExportSessionTests.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = SJSAssetExportSessionTests.swift; sourceTree = "<group>"; };
+		7B9BC0272C30612C00C160C2 /* ExportSession.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = ExportSession.swift; sourceTree = "<group>"; };
 /* End PBXFileReference section */
 
 /* Begin PBXFrameworksBuildPhase section */
@@ -73,6 +77,8 @@
 			children = (
 				7B9BC00C2C305D2C00C160C2 /* SJSAssetExportSession.h */,
 				7B9BC00D2C305D2C00C160C2 /* SJSAssetExportSession.docc */,
+				7B9BC0272C30612C00C160C2 /* ExportSession.swift */,
+				7B7AE3082C36615700DB7391 /* SampleWriter.swift */,
 			);
 			path = SJSAssetExportSession;
 			sourceTree = "<group>";
@@ -194,6 +200,8 @@
 			isa = PBXSourcesBuildPhase;
 			buildActionMask = 2147483647;
 			files = (
+				7B7AE3092C36615700DB7391 /* SampleWriter.swift in Sources */,
+				7B9BC0282C30612C00C160C2 /* ExportSession.swift in Sources */,
 				7B9BC00E2C305D2C00C160C2 /* SJSAssetExportSession.docc in Sources */,
 			);
 			runOnlyForDeploymentPostprocessing = 0;
@@ -276,6 +284,7 @@
 				ONLY_ACTIVE_ARCH = YES;
 				SWIFT_ACTIVE_COMPILATION_CONDITIONS = "DEBUG $(inherited)";
 				SWIFT_OPTIMIZATION_LEVEL = "-Onone";
+				SWIFT_VERSION = 6.0;
 				VERSIONING_SYSTEM = "apple-generic";
 				VERSION_INFO_PREFIX = "";
 			};
@@ -332,6 +341,7 @@
 				MTL_ENABLE_DEBUG_INFO = NO;
 				MTL_FAST_MATH = YES;
 				SWIFT_COMPILATION_MODE = wholemodule;
+				SWIFT_VERSION = 6.0;
 				VERSIONING_SYSTEM = "apple-generic";
 				VERSION_INFO_PREFIX = "";
 			};
@@ -362,7 +372,7 @@
 					"@executable_path/../Frameworks",
 					"@loader_path/Frameworks",
 				);
-				MACOSX_DEPLOYMENT_TARGET = 14.5;
+				MACOSX_DEPLOYMENT_TARGET = 15.0;
 				MARKETING_VERSION = 1.0;
 				MODULE_VERIFIER_SUPPORTED_LANGUAGES = "objective-c objective-c++";
 				MODULE_VERIFIER_SUPPORTED_LANGUAGE_STANDARDS = "gnu17 gnu++20";
@@ -373,7 +383,6 @@
 				SUPPORTED_PLATFORMS = "iphoneos iphonesimulator macosx xros xrsimulator";
 				SWIFT_EMIT_LOC_STRINGS = YES;
 				SWIFT_INSTALL_OBJC_HEADER = NO;
-				SWIFT_VERSION = 5.0;
 				TARGETED_DEVICE_FAMILY = "1,2,7";
 				XROS_DEPLOYMENT_TARGET = 2.0;
 			};
@@ -404,7 +413,7 @@
 					"@executable_path/../Frameworks",
 					"@loader_path/Frameworks",
 				);
-				MACOSX_DEPLOYMENT_TARGET = 14.5;
+				MACOSX_DEPLOYMENT_TARGET = 15.0;
 				MARKETING_VERSION = 1.0;
 				MODULE_VERIFIER_SUPPORTED_LANGUAGES = "objective-c objective-c++";
 				MODULE_VERIFIER_SUPPORTED_LANGUAGE_STANDARDS = "gnu17 gnu++20";
@@ -415,7 +424,6 @@
 				SUPPORTED_PLATFORMS = "iphoneos iphonesimulator macosx xros xrsimulator";
 				SWIFT_EMIT_LOC_STRINGS = YES;
 				SWIFT_INSTALL_OBJC_HEADER = NO;
-				SWIFT_VERSION = 5.0;
 				TARGETED_DEVICE_FAMILY = "1,2,7";
 				XROS_DEPLOYMENT_TARGET = 2.0;
 			};
@@ -437,7 +445,6 @@
 				SDKROOT = auto;
 				SUPPORTED_PLATFORMS = "iphoneos iphonesimulator macosx xros xrsimulator";
 				SWIFT_EMIT_LOC_STRINGS = NO;
-				SWIFT_VERSION = 5.0;
 				TARGETED_DEVICE_FAMILY = "1,2,7";
 				XROS_DEPLOYMENT_TARGET = 2.0;
 			};
@@ -459,7 +466,6 @@
 				SDKROOT = auto;
 				SUPPORTED_PLATFORMS = "iphoneos iphonesimulator macosx xros xrsimulator";
 				SWIFT_EMIT_LOC_STRINGS = NO;
-				SWIFT_VERSION = 5.0;
 				TARGETED_DEVICE_FAMILY = "1,2,7";
 				XROS_DEPLOYMENT_TARGET = 2.0;
 			};

SJSAssetExportSession/ExportSession.swift

@@ -0,0 +1,52 @@
+//
+//  ExportSession.swift
+//  SJSAssetExportSession
+//
+//  Created by Sami Samhuri on 2024-06-29.
+//
+
+public import AVFoundation
+
+public final class ExportSession {
+    public enum Error: LocalizedError {
+        case setupFailure(reason: String)
+        case readFailure((any Swift.Error)?)
+        case writeFailure((any Swift.Error)?)
+
+        public var errorDescription: String? {
+            switch self {
+            case let .setupFailure(reason):
+                reason
+            case let .readFailure(underlyingError):
+                underlyingError?.localizedDescription ?? "Unknown read failure"
+            case let .writeFailure(underlyingError):
+                underlyingError?.localizedDescription ?? "Unknown write failure"
+            }
+        }
+    }
+
+    public func export(
+        asset: sending AVAsset,
+        audioMix: sending AVAudioMix?,
+        audioOutputSettings: [String: (any Sendable)],
+        videoComposition: sending AVVideoComposition?,
+        videoOutputSettings: [String: (any Sendable)],
+        timeRange: CMTimeRange? = nil,
+        optimizeForNetworkUse: Bool = false,
+        to outputURL: URL,
+        as fileType: AVFileType
+    ) async throws {
+        let sampleWriter = try await SampleWriter(
+            asset: asset,
+            timeRange: timeRange ?? CMTimeRange(start: .zero, duration: .positiveInfinity),
+            audioMix: audioMix,
+            audioOutputSettings: audioOutputSettings,
+            videoComposition: videoComposition,
+            videoOutputSettings: videoOutputSettings,
+            optimizeForNetworkUse: optimizeForNetworkUse,
+            outputURL: outputURL,
+            fileType: fileType
+        )
+        try await sampleWriter.writeSamples()
+    }
+}

SJSAssetExportSession/SampleWriter.swift

@@ -0,0 +1,259 @@
+//
+//  SampleWriter.swift
+//  SJSAssetExportSession
+//
+//  Created by Sami Samhuri on 2024-07-03.
+//
+
+import AVFoundation.AVAsset
+
+private extension AVAsset {
+    func sendTracks(withMediaType mediaType: AVMediaType) async throws -> sending [AVAssetTrack] {
+        try await loadTracks(withMediaType: mediaType)
+    }
+}
+
+actor SampleWriter {
+    private let queue = DispatchSerialQueue(
+        label: "SJSAssetExportSession.SampleWriter",
+        autoreleaseFrequency: .workItem,
+        target: .global()
+    )
+
+    public nonisolated var unownedExecutor: UnownedSerialExecutor {
+        queue.asUnownedSerialExecutor()
+    }
+
+    let audioTracks: [AVAssetTrack]
+
+    let audioMix: AVAudioMix?
+
+    let audioOutputSettings: [String: (any Sendable)]
+
+    let videoTracks: [AVAssetTrack]
+
+    let videoComposition: AVVideoComposition?
+
+    let videoOutputSettings: [String: (any Sendable)]
+
+    let reader: AVAssetReader
+
+    let writer: AVAssetWriter
+
+    let duration: CMTime
+
+    let timeRange: CMTimeRange
+
+    private var audioOutput: AVAssetReaderAudioMixOutput?
+
+    private var audioInput: AVAssetWriterInput?
+
+    private var videoOutput: AVAssetReaderVideoCompositionOutput?
+
+    private var videoInput: AVAssetWriterInput?
+
+    private var pixelBufferAdaptor: AVAssetWriterInputPixelBufferAdaptor?
+
+    init(
+        asset: sending AVAsset,
+        timeRange: CMTimeRange,
+        audioMix: AVAudioMix?,
+        audioOutputSettings: sending [String: (any Sendable)],
+        videoComposition: AVVideoComposition?,
+        videoOutputSettings: sending [String: (any Sendable)],
+        optimizeForNetworkUse: Bool,
+        outputURL: URL,
+        fileType: AVFileType
+    ) async throws {
+        let duration =
+        if timeRange.duration.isValid && !timeRange.duration.isPositiveInfinity {
+            timeRange.duration
+        } else {
+            try await asset.load(.duration)
+        }
+
+        let reader = try AVAssetReader(asset: asset)
+        reader.timeRange = timeRange
+
+        let writer = try AVAssetWriter(outputURL: outputURL, fileType: fileType)
+        writer.shouldOptimizeForNetworkUse = optimizeForNetworkUse
+        guard writer.canApply(outputSettings: videoOutputSettings, forMediaType: .video) else {
+            throw ExportSession.Error.setupFailure(reason: "Cannot apply video output settings")
+        }
+
+        self.audioTracks = try await asset.sendTracks(withMediaType: .audio)
+        self.audioMix = audioMix
+        self.audioOutputSettings = audioOutputSettings
+        self.videoTracks = try await asset.sendTracks(withMediaType: .video)
+        self.videoComposition = videoComposition
+        self.videoOutputSettings = videoOutputSettings
+        self.reader = reader
+        self.writer = writer
+        self.duration = duration
+        self.timeRange = timeRange
+    }
+
+    func writeSamples() async throws {
+        writer.startWriting()
+        reader.startReading()
+        writer.startSession(atSourceTime: timeRange.start)
+
+        async let audioResult = try encodeAudioTracks(audioTracks)
+        async let videoResult = try encodeVideoTracks(videoTracks)
+        _ = try await (audioResult, videoResult)
+
+        if reader.status == .cancelled || writer.status == .cancelled {
+            throw CancellationError()
+        } else if writer.status == .failed {
+            reader.cancelReading()
+            throw ExportSession.Error.writeFailure(writer.error)
+        } else if reader.status == .failed {
+            writer.cancelWriting()
+            throw ExportSession.Error.readFailure(reader.error)
+        } else {
+            await withCheckedContinuation { continuation in
+                writer.finishWriting {
+                    continuation.resume(returning: ())
+                }
+            }
+        }
+    }
+
+    private func encodeAudioTracks(_ audioTracks: [AVAssetTrack]) async throws -> Bool {
+        guard !audioTracks.isEmpty else { return false }
+
+        let audioOutput = AVAssetReaderAudioMixOutput(audioTracks: audioTracks, audioSettings: nil)
+        guard reader.canAdd(audioOutput) else {
+            throw ExportSession.Error.setupFailure(reason: "Can't add audio output to reader")
+        }
+        reader.add(audioOutput)
+        self.audioOutput = audioOutput
+
+        let audioInput = AVAssetWriterInput(mediaType: .audio, outputSettings: audioOutputSettings)
+        guard writer.canAdd(audioInput) else {
+            throw ExportSession.Error.setupFailure(reason: "Can't add audio input to writer")
+        }
+        writer.add(audioInput)
+        self.audioInput = audioInput
+
+        return await withCheckedContinuation { continuation in
+            self.audioInput?.requestMediaDataWhenReady(on: queue) {
+                let hasMoreSamples = self.assumeIsolated { $0.writeReadyAudioSamples() }
+                if !hasMoreSamples {
+                    continuation.resume(returning: true)
+                }
+            }
+        }
+    }
+
+    private func writeReadyAudioSamples() -> Bool {
+        guard let audioOutput, let audioInput else { return true }
+
+        while audioInput.isReadyForMoreMediaData {
+            guard reader.status == .reading && writer.status == .writing,
+                  let sampleBuffer = audioOutput.copyNextSampleBuffer() else {
+                audioInput.markAsFinished()
+                NSLog("Finished encoding ready audio samples from \(audioOutput)")
+                return false
+            }
+
+            guard audioInput.append(sampleBuffer) else {
+                NSLog("Failed to append audio sample buffer \(sampleBuffer) to input \(audioInput)")
+                return false
+            }
+        }
+
+        // Everything was appended successfully, return true indicating there's more to do.
+        NSLog("Completed encoding ready audio samples, more to come...")
+        return true
+    }
+
+    private func encodeVideoTracks(_ videoTracks: [AVAssetTrack]) async throws -> Bool {
+        guard !videoTracks.isEmpty else { return false }
+
+        guard let width = videoComposition.map({ Int($0.renderSize.width) })
+                ?? (videoOutputSettings[AVVideoWidthKey] as? NSNumber)?.intValue,
+              let height = videoComposition.map({ Int($0.renderSize.height) })
+                ?? (videoOutputSettings[AVVideoHeightKey] as? NSNumber)?.intValue else {
+            throw ExportSession.Error.setupFailure(reason: "Export dimensions must be provided in a video composition or video output settings")
+        }
+
+        let videoOutput = AVAssetReaderVideoCompositionOutput(videoTracks: videoTracks, videoSettings: nil)
+        videoOutput.alwaysCopiesSampleData = false
+        videoOutput.videoComposition = videoComposition
+        guard reader.canAdd(videoOutput) else {
+            throw ExportSession.Error.setupFailure(reason: "Can't add video output to reader")
+        }
+        reader.add(videoOutput)
+        self.videoOutput = videoOutput
+
+        let videoInput = AVAssetWriterInput(mediaType: .video, outputSettings: videoOutputSettings)
+        guard writer.canAdd(videoInput) else {
+            throw ExportSession.Error.setupFailure(reason: "Can't add video input to writer")
+        }
+        writer.add(videoInput)
+        self.videoInput = videoInput
+
+        let pixelBufferAttributes: [String: Any] = [
+            kCVPixelBufferPixelFormatTypeKey as String: NSNumber(integerLiteral: Int(kCVPixelFormatType_32RGBA)),
+            kCVPixelBufferWidthKey as String: NSNumber(integerLiteral: width),
+            kCVPixelBufferHeightKey as String: NSNumber(integerLiteral: height),
+            "IOSurfaceOpenGLESTextureCompatibility": NSNumber(booleanLiteral: true),
+            "IOSurfaceOpenGLESFBOCompatibility": NSNumber(booleanLiteral: true),
+        ]
+        pixelBufferAdaptor = AVAssetWriterInputPixelBufferAdaptor(
+            assetWriterInput: videoInput,
+            sourcePixelBufferAttributes: pixelBufferAttributes
+        )
+
+        return await withCheckedContinuation { continuation in
+            self.videoInput?.requestMediaDataWhenReady(on: queue) {
+                let hasMoreSamples = self.assumeIsolated { $0.writeReadyVideoSamples() }
+                if !hasMoreSamples {
+                    continuation.resume(returning: true)
+                }
+            }
+        }
+    }
+
+    private func writeReadyVideoSamples() -> Bool {
+        guard let videoOutput, let videoInput, let pixelBufferAdaptor else { return true }
+
+        while videoInput.isReadyForMoreMediaData {
+            guard reader.status == .reading && writer.status == .writing,
+                  let sampleBuffer = videoOutput.copyNextSampleBuffer() else {
+                videoInput.markAsFinished()
+                NSLog("Finished encoding ready video samples from \(videoOutput)")
+                return false
+            }
+
+            let samplePresentationTime = CMSampleBufferGetPresentationTimeStamp(sampleBuffer) - timeRange.start
+            let progress = Float(samplePresentationTime.seconds / duration.seconds)
+#warning("TODO: publish progress to an AsyncStream")
+
+            guard let pixelBufferPool = pixelBufferAdaptor.pixelBufferPool else {
+                NSLog("No pixel buffer pool available on adaptor \(pixelBufferAdaptor)")
+                return false
+            }
+            var toRenderBuffer: CVPixelBuffer?
+            let result = CVPixelBufferPoolCreatePixelBuffer(kCFAllocatorDefault, pixelBufferPool, &toRenderBuffer)
+            var handled = false
+            if result == kCVReturnSuccess, let toBuffer = toRenderBuffer {
+                handled = pixelBufferAdaptor.append(toBuffer, withPresentationTime: samplePresentationTime)
+                if !handled { return false }
+            }
+            if !handled {
+#warning("is this really necessary?! seems like a failure scenario...")
+                guard videoInput.append(sampleBuffer) else {
+                    NSLog("Failed to append video sample buffer \(sampleBuffer) to input \(videoInput)")
+                    return false
+                }
+            }
+        }
+
+        // Everything was appended successfully, return true indicating there's more to do.
+        NSLog("Completed encoding ready video samples, more to come...")
+        return true
+    }
+
+}