ios - Xamarin降低影片大小

Question

我想在Xamarin(iOS)中“压缩”视频(用于上传)。
我发现了有关AVAssetWriter类的信息，我可以设置分辨率，比特率等。
您将如何使用它？还有哪几类？
您可能已经注意到，对于应用程序开发来说，它是非常新的。

Answer 1

这是一个使用AVAssetReader将AVAssetWriter馈送给的示例，以重新采样和/或转码视频。

在此示例中，我正在拍摄包含在应用程序捆绑包(BundleResource)中的名为“Pool.mp4”的视频，并以1Mbps的大小将300x300的大小作为“NewVideo.mp4”保存到“tmp”目录中(缩小原始文件大小增加约50％...)

注意:不会检查返回值或错误代码，这些将留给实现者。

var asset = AVAsset.FromUrl(NSUrl.FromFilename("Pool.mp4"));
NSError assetReaderError;
var assetReader = AVAssetReader.FromAsset(asset, out assetReaderError);
var assetTrack = asset.Tracks.First();
var inputSettings = new AVVideoSettingsUncompressed() 
{
    Height = 300,
    Width = 300,
};
var assetReaderOutput = new AVAssetReaderTrackOutput(assetTrack, settings: inputSettings);
assetReaderOutput.AlwaysCopiesSampleData = false;

string tempFile = Path.Combine(Path.GetTempPath(), "NewVideo.mp4");
if (File.Exists(tempFile)) File.Delete(tempFile);
var url = NSUrl.FromFilename(tempFile);
NSError assetWriterError;
var assetWriter = new AVAssetWriter(url, AVFileType.Mpeg4, out assetWriterError);
var outputSettings = new AVVideoSettingsCompressed()
{
    Height = 300,
    Width = 300,
    Codec = AVVideoCodec.H264,
    CodecSettings = new AVVideoCodecSettings
    {
        AverageBitRate = 1000000
    }
};
var assetWriterInput = new AVAssetWriterInput(mediaType: AVMediaType.Video, outputSettings: outputSettings);
assetWriterInput.ExpectsMediaDataInRealTime = false;
assetWriter.AddInput(assetWriterInput);

assetWriter.StartWriting();
assetReader.AddOutput(assetReaderOutput);
assetReader.StartReading();
assetWriter.StartSessionAtSourceTime(CoreMedia.CMTime.Zero);

var mediaInputQueue = new DispatchQueue("mediaInputQueue");
assetWriterInput.RequestMediaData(mediaInputQueue, () =>
{
    while (assetWriterInput.ReadyForMoreMediaData)
    {
        var nextBuffer = assetReaderOutput.CopyNextSampleBuffer();
        if (nextBuffer != null)
        {
            assetWriterInput.AppendSampleBuffer(nextBuffer);
        }
        else
        {
            assetWriterInput.MarkAsFinished();
            assetWriter.FinishWritingAsync();
            assetReader.CancelReading();
            assetReader.Dispose();
            assetReaderOutput.Dispose();
            assetWriter.Dispose();
            assetWriterInput.Dispose();
            break;
        }
    }
});