extract from ipod-library about just_waveform

[ryanheise]

This plugin only extracts data from a file. It's up to you to get the data from other sources and save them to a file. Once you do so, this plugin is applicable after that point. I can't help you with how to read data from various sources, you will need to search for other plugins to do that or write a plugin that does that.

[LondonX]

Thanks for reply. Yes, I write a plugin to do that, post here hope to help other guys.

Dart call

final exported = await AvAssetExportIos.instance.export(
      ipodLibraryUri: song.data,
      targetUri: iosExportFile.uri.toString(),
    );

SwiftAvAssetExportIosPlugin.swift

import Flutter
import UIKit
import AVFoundation
import AVKit
import AssetsLibrary

public class SwiftAvAssetExportIosPlugin: NSObject, FlutterPlugin {
    public static func register(with registrar: FlutterPluginRegistrar) {
        let channel = FlutterMethodChannel(name: "av_asset_export_ios", binaryMessenger: registrar.messenger())
        let instance = SwiftAvAssetExportIosPlugin()
        registrar.addMethodCallDelegate(instance, channel: channel)
    }
    
    public func handle(_ call: FlutterMethodCall, result: @escaping FlutterResult) {
        let args = call.arguments as? [String : Any?]
        switch(call.method) {
        case "export":
            let ipodLibraryUri = args!["ipodLibraryUri"] as! String
            let targetUri = args!["targetUri"] as! String
            let assetURL = URL.init(string: ipodLibraryUri)!
            let targetURL = URL.init(string: targetUri)!
            export(assetURL, targetURL) { error in
                print("[SwiftAvAssetExportIosPlugin] has error", error != nil)
                result(error == nil)
            }
            break
        default:
            result(FlutterMethodNotImplemented)
        }
    }
    
    func export(
        _ assetURL: URL,
        _ targetURL: URL,
        completionHandler: @escaping (_ error: Error?) -> ()
    ) {
        let asset = AVURLAsset(url: assetURL)
        guard let exporter = AVAssetExportSession(
            asset: asset,
            presetName: AVAssetExportPresetAppleM4A
        ) else {
            completionHandler(ExportError.unableToCreateExporter)
            return
        }
        try? FileManager.default.removeItem(at: targetURL)
        exporter.outputURL = targetURL
        exporter.outputFileType = AVFileType.m4a
        
        print("[SwiftAvAssetExportIosPlugin] exportAsynchronously assetURL: \(assetURL), outputURL: \(targetURL)");
        exporter.exportAsynchronously {
            switch(exporter.status) {
            case .completed:
                completionHandler(nil)
                break
            case .failed:
                print(exporter.error!)
                completionHandler(exporter.error)
                break
            default:
                break
            }
        }
    }
}

enum ExportError: Error {
    case unableToCreateExporter
    case unsupportedFormat
}