以Xamarin形式将视频文件转换为音频文件 [英] Covert video file to audio file in Xamarin Forms

问题描述

我正在尝试创建一个允许用户在Xamarin.Forms中下载youtube视频的音频的应用.我可以使用"VideoLibrary"下载视频，并在C#控制台应用程序中使用"MediaToolkit"将其转换为mp3.

I am trying to create an app that allows a user to download the audio of youtube videos in Xamarin.Forms. I can download the video using 'VideoLibrary' and convert it to an mp3 using 'MediaToolkit' in a C# Console Application without any errors.

static void DownloadAudio(string videoUrl, string saveDir)
{
    YouTube youtube = YouTube.Default;
    Video vid = youtube.GetVideo(videoUrl);
    File.WriteAllBytes(saveDir + vid.FullName, vid.GetBytes());

    string originalFile = saveDir + vid.FullName;
    var inputFile = new MediaToolkit.Model.MediaFile { Filename = saveDir + vid.FullName };
    var outputFile = new MediaToolkit.Model.MediaFile { Filename = $"{saveDir + vid.FullName}.mp3" };

    using (var engine = new MediaToolkit.Engine())
    {
        engine.GetMetadata(inputFile);

        engine.Convert(inputFile, outputFile);
        if (File.Exists(originalFile))
        {
            File.Delete(originalFile);
        }
    }
}

问题是，这在Xamarin中不起作用.只能安装nuget软件包的便携式版本，该版本不包含 Engine 或 MediaFile 的定义.

The problem is that this won't work in Xamarin. Only the portable version of the nuget package can be installed which doesn't contain definitions for Engine or MediaFile.

此外，并不是所有的视频都以 .mp4 的形式下载，有些则以 .webm 的形式下载.我需要输出文件都为 .mp3 和 .mp4 .

Furthermore, not all videos download as .mp4, some download as .webm. I need the output files to be both .mp3 and .mp4.

如何在Xamarin.Forms中将视频文件转换为音频文件?

How can I convert the video files into audio files in Xamarin.Forms?

推荐答案

如果PCL无法使用它，则可以选择平台依赖项.基本上，您会为所需的功能创建一个接口，在特定于平台的项目中实现这些类，然后使用 DependencyAttribute .现在，您可以从PCL中使用 DependencyService 获取实例(请参见此处和此处).

If it's not available from a PCL, you could opt to platform dependencies. Basically you create an interface for the functionality you need, implement the classes in your platform specific projects and export them with the DependencyAttribute. From your PCL you can now obtain an instance with the DependencyService (see here and here).

界面可能如下所示

public interface IMediaHelper
{
    void ConvertToMp3(string fullFileName);
}

及其实现(在您的iOS和Android项目中-使用SharedProject避免代码重复)

and the implementation (in your iOS and Android projects - use a SharedProject to avoid code duplication)

[assembly: Dependency(typeof(MediaHelper))]

public class MediaHelper
{
    public void ConvertToMp3(string fullFileName)
    {
        var infile = new MediaToolkit.Model.MediaFile { Filename = fullFileName;
        var outfile = new MediaToolkit.Model.MediaFile { Filename = $"{fullFileName}.mp3" };

        using (var engine = new MediaToolkit.Engine())
        {
            engine.GetMetadata(infile);

            engine.Convert(infile, outfile);
            if (File.Exists(fullFileName))
            {
                File.Delete(fullFileName);
            }
        }
    }
}

因此，您的客户代码应为

Consequently your client code would be

void DownloadAudio(string videoUrl, string saveDir)
{
    YouTube youtube = YouTube.Default;
    Video vid = youtube.GetVideo(videoUrl);

    var fullFileName = Path.Combine(saveDir, vid.FullName);

    File.WriteAllBytes(fullFileName, vid.GetBytes());

    var mediaHelper = DependencyService.Get<IMediaHelper>();
    mediaHelper.ConvertToMp3(fullFileName);
}

请注意:我已将对路径和文件的手动连接替换为对 Path.Combine 的调用，该调用可处理路径已附带的情况路径分隔符.此外，它可以为您处理不同的平台.

Please Note: I have replaced the manual concatenation of the path and the file with the call to Path.Combine, which handles cases in which the path already comes with the path separator. Furthermore it handles the different platforms for you.

显然，MediaToolkit至少在Android上不起作用，因此，您必须采用相同的方式-使用平台依赖性-并用开箱即用的方式实现所需的功能.请参阅此答案有关如何从视频中提取PCM数据和

Obviously MediaToolkit won't work for Android (at least), hence you'll have to go the same way - with the platform dependencies - and implement what you need with what you've got out-of-the-box. See this answer on how to extract PCM data from a video and this one on how to convert PCM to MP3 - just to give you an idea.

请注意

[...]如果要对mp3文件进行编码/解码，则可能需要支付许可证/专利费.

[...] if you want to encode/decode a mp3 file you may have to pay license/patent fees.

源

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