konverter/Sources/Konverter/Convert/FFmpeg.swift

import Foundation

/// ffmpeg back end. Used for containers and codecs Apple's frameworks cannot
/// write. Progress is parsed from `-progress pipe:1`.
enum FFmpeg {
    static func convert(
        source: URL,
        to format: Format,
        at destination: URL,
        bitrate: String = "128",
        quality: String = "Medium",
        cancellation: Cancellation? = nil,
        progress: ((Double) -> Void)? = nil
    ) throws {
        guard let ffmpeg = Toolchain.ffmpeg, Settings.shared.useExternalTools else {
            throw ConversionError.missingTool("\(format.displayName) requires ffmpeg — install it with: brew install ffmpeg")
        }

        var arguments = ["-y", "-hide_banner", "-loglevel", "error", "-i", source.path]
        arguments += encodingArguments(for: format, bitrate: bitrate, quality: quality)
        arguments += ["-progress", "pipe:1", "-nostats"]
        arguments.append(destination.path)

        let duration = AVConverter.duration(source) ?? 0
        try Shell.runReportingProgress(ffmpeg, arguments, cancellation: cancellation) { _, line in
            guard let progress, duration > 0 else { return }
            if let range = line.range(of: "out_time_us="),
               let microseconds = Double(line[range.upperBound...].trimmingCharacters(in: .whitespaces)) {
                progress(min(1, microseconds / 1_000_000 / duration))
            }
        }
        progress?(1)
    }

    /// Down-mixes any media to audio.
    static func extractAudio(
        source: URL,
        to format: Format,
        at destination: URL,
        bitrate: String = "192",
        cancellation: Cancellation? = nil,
        progress: ((Double) -> Void)? = nil
    ) throws {
        try convert(source: source, to: format, at: destination, bitrate: bitrate, cancellation: cancellation, progress: progress)
    }

    /// Progress-reporting pass-through for tools (trim, speed, gain, …).
    static func filter(
        source: URL,
        at destination: URL,
        arguments: [String],
        cancellation: Cancellation? = nil,
        progress: ((Double) -> Void)? = nil
    ) throws {
        guard let ffmpeg = Toolchain.ffmpeg, Settings.shared.useExternalTools else {
            throw ConversionError.missingTool("This tool requires ffmpeg — install it with: brew install ffmpeg")
        }
        var full = ["-y", "-hide_banner", "-loglevel", "error", "-i", source.path]
        full += arguments
        full += ["-progress", "pipe:1", "-nostats", destination.path]

        let duration = AVConverter.duration(source) ?? 0
        try Shell.runReportingProgress(ffmpeg, full, cancellation: cancellation) { _, line in
            guard let progress, duration > 0 else { return }
            if let range = line.range(of: "out_time_us="),
               let microseconds = Double(line[range.upperBound...].trimmingCharacters(in: .whitespaces)) {
                progress(min(1, microseconds / 1_000_000 / duration))
            }
        }
        progress?(1)
    }

    private static func encodingArguments(for format: Format, bitrate: String, quality: String) -> [String] {
        let audioRate = "\(bitrate)k"
        switch format {
        case .mp3: return ["-vn", "-c:a", "libmp3lame", "-b:a", audioRate]
        case .m4a: return ["-vn", "-c:a", "aac", "-b:a", audioRate]
        case .wav: return ["-vn", "-c:a", "pcm_s16le"]
        case .aiff: return ["-vn", "-c:a", "pcm_s16be"]
        case .flac: return ["-vn", "-c:a", "flac"]
        case .ogg: return ["-vn", "-c:a", "libvorbis", "-q:a", "5"]
        case .opus: return ["-vn", "-c:a", "libopus", "-b:a", audioRate]
        case .wma: return ["-vn", "-c:a", "wmav2", "-b:a", audioRate]
        case .mkv: return videoArguments(codec: "libx264", quality: quality) + ["-c:a", "aac", "-b:a", audioRate]
        case .webm: return ["-c:v", "libvpx-vp9", "-crf", "32", "-b:v", "0", "-c:a", "libopus", "-b:a", audioRate]
        case .avi: return ["-c:v", "mpeg4", "-q:v", "5", "-c:a", "libmp3lame", "-b:a", audioRate]
        case .wmv: return ["-c:v", "wmv2", "-b:v", "2M", "-c:a", "wmav2", "-b:a", audioRate]
        case .mp4, .mov, .m4v, .gif: return videoArguments(codec: "libx264", quality: quality) + ["-c:a", "aac", "-b:a", audioRate]
        default: return []
        }
    }

    private static func videoArguments(codec: String, quality: String) -> [String] {
        let crf: String
        switch quality {
        case "Low": crf = "30"
        case "High": crf = "20"
        default: crf = "25"
        }
        return ["-c:v", codec, "-preset", "medium", "-crf", crf, "-pix_fmt", "yuv420p"]
    }
}

/// CoreAudio's `afconvert`: always present, handles PCM containers and
/// channel remapping without any third-party install.
enum CoreAudio {
    static func convert(
        source: URL,
        to format: Format,
        at destination: URL,
        cancellation: Cancellation? = nil
    ) throws {
        guard let fileFormat = coreAudioFileFormat(for: format) else {
            throw ConversionError.unsupported("CoreAudio cannot write \(format.displayName).")
        }
        do {
            try Shell.run(
                Toolchain.afconvert,
                ["-f", fileFormat, "-d", dataFormat(for: fileFormat), source.path, destination.path],
                cancellation: cancellation
            )
        } catch {
            throw ConversionError.failed("CoreAudio could not convert \(source.lastPathComponent): \((error as? LocalizedError)?.errorDescription ?? error.localizedDescription)")
        }
    }

    static func remix(
        source: URL,
        at destination: URL,
        mono: Bool,
        cancellation: Cancellation? = nil
    ) throws {
        try Shell.run(
            Toolchain.afconvert,
            ["-f", "caff", "-d", "LEI16", "-c", mono ? "1" : "2", source.path, destination.path],
            cancellation: cancellation
        )
    }

    private static func coreAudioFileFormat(for format: Format) -> String? {
        switch format {
        case .wav: return "WAVE"
        case .aiff: return "AIFF"
        case .m4a: return "m4af"
        default: return nil
        }
    }

    private static func dataFormat(for fileFormat: String) -> String {
        switch fileFormat {
        case "WAVE": return "LEI16"
        case "AIFF": return "BEI16"
        default: return "aac"
        }
    }
}