如何从 Objective-C 中未显示的视频生成视频缩略图

Question

对于 Objective-C 中的 iOS 项目，我需要显示屏幕上未显示的 rtsp 视频流的缩略图（我无法截图）。 我的视图显示一个视频流和其他流的三个缩略图（定期刷新），以便用户可以在它们之间切换。

那么，我怎样才能生成这个缩略图呢？ 我正在使用 MobileVLCKit 来显示我的主视频流（如果可能的话，我更愿意使用这个框架来生成我的缩略图......）。

我在论坛和谷歌结果中找到了很多结果，但没有一个符合我的情况：流+不显示视频。

感谢您的帮助！

编辑：

我也尝试过VLC的缩略图，但没有成功：

VLCMedia *media = [VLCMedia mediaWithURL:[NSURL URLWithString:<Rtsp Url>]];
thumbnailer = [VLCMediaThumbnailer thumbnailerWithMedia:media andDelegate:self];

但我总是陷入 mediaThumbnailerDidTimeOut 委托方法。

Answer 1

基本上您需要做的就是使用 VLCKit 'VLCMediaThumbnailer' 类并实现 'VLCMediaThumbnailerDelegate' 所需的两个函数

这是一个 Objective-C 示例：

@implementation DummyObject <VLCMediaThumbnailerDelegate>

- (void)workerMethod
{
    NSURL *url = [NSURL urlWithString:@""];
    VLCMedia *media = [VLCMedia mediaWithURL:url];

    VLCMediaThumbnailer *thumbnailer = [VLCMediaThumbnailer thumbnailerWithMedia:media delegate:self];

    CGSize thumbSize = CGSizeMake(800.,600.);
    thumbnailer.thumbnailWidth = thumbSize.width;
    thumbnailer.thumbnailHeight = thumbSize.height;

    [thumbnailer fetchThumbnail];
}

- (void)mediaThumbnailer:(VLCMediaThumbnailer *)mediaThumbnailer didFinishThumbnail:(CGImageRef)thumbnail
{
    if (thumbnail) {
        UIImage *thumbnailImage = [UIImage imageWithCGImage:thumbnail scale:[UIScreen mainScreen].scale orientation:UIImageOrientationUp];
        if (thumbnailImage) {
            // do something with the thumbnail
        }
    }
}

- (void)mediaThumbnailerDidTimeOut:(VLCMediaThumbnailer *)mediaThumbnailer
{
     // show error generating thumbnail
}

@end

Objective-C 代码的学分

这就是它在 swift 和 SwiftUI 中的样子

func generateThumbnails()
{
    if mediaPlayer.media != nil
    {
        let vlcMediaThumbnailer: VLCMediaThumbnailer = VLCMediaThumbnailer(media: mediaPlayer.media, andDelegate: self)
        vlcMediaThumbnailer.thumbnailWidth = 440
        vlcMediaThumbnailer.thumbnailHeight = 225
        vlcMediaThumbnailer.snapshotPosition = 0.5 // get thumbs from the middle of the video

        vlcMediaThumbnailer.fetchThumbnail()
    }
}

func mediaThumbnailerDidTimeOut(_ mediaThumbnailer: VLCMediaThumbnailer!)
{
    print("failed generating thumbnail")
}

func mediaThumbnailer(_ mediaThumbnailer: VLCMediaThumbnailer!, didFinishThumbnail thumbnail: CGImage!)
{
    print("got another thumbnail - do something with it")
}

这里是 tvOS 14.7 和 SwiftUI 中的 apple-tv 的 完整工作演示，用于 VLCKit 中的 缩略图：

import SwiftUI
import AVFoundation

class VideoModel: ObservableObject
{
    @Published var thumbnails: [Image] = []
    var videoUrl: String = ""
    let thumbnailWidth: CGFloat = 400.0
    let thumbnailHeight: CGFloat = 225.0
}

struct VLCPlayerTestView: View
{
    @State var isPlayVideo: Bool = false
    
    let videoUrl: String = "https://upload.wikimedia.org/wikipedia/commons/transcoded/c/c0/Big_Buck_Bunny_4K.webm/Big_Buck_Bunny_4K.webm.480p.vp9.webm"
    var videoPlayer: VideoPlayer? = nil
    @ObservedObject var videoModel = VideoModel()
    
    init()
    {
        videoModel.videoUrl = videoUrl
        videoPlayer = VideoPlayer(videoModel: videoModel)
    }
    
    var body: some View
    {
        HStack(spacing: 20)
        {
            ForEach(0..<videoModel.thumbnails.count, id: \.self) { itemIndex in
                videoModel.thumbnails[itemIndex]
                    .resizable()
                    .aspectRatio(contentMode: .fill)
                    .frame(width: videoModel.thumbnailWidth, height: videoModel.thumbnailHeight, alignment: Alignment.center)
                    .focusable()
                    .onLongPressGesture(minimumDuration: 0.01) {
                        isPlayVideo = true
                    }
            }
        }
        .fullScreenCover(isPresented: $isPlayVideo)
        {
            videoPlayer
                .edgesIgnoringSafeArea(.all)
                .onAppear {
                    videoPlayer!.player.playVideo()
                }
                .onDisappear {
                    videoPlayer!.player.stopVideo()
                }
        }
    }
}

struct VideoPlayer: UIViewRepresentable
{
    var player: VLCPlayerView
    
    init(videoModel: VideoModel)
    {
        player = VLCPlayerView()
        player.videoModel = videoModel
        player.loadMedia()
        player.generateThumbnails()
    }

    func updateUIView(_ uiView: UIView, context: UIViewRepresentableContext<VideoPlayer>)
    {
    }

    func makeUIView(context: Context) -> UIView
    {
        return player
    }
}




class VLCPlayerView: UIView, VLCMediaPlayerDelegate, VLCMediaThumbnailerDelegate
{
    var videoModel: VideoModel?
    let mediaPlayer: VLCMediaPlayer = VLCMediaPlayer()

    override init(frame: CGRect)
    {
        super.init(frame: frame)
    }
    
    func loadMedia()
    {
        if !videoModel!.videoUrl.isEmpty
        {
            mediaPlayer.media = VLCMedia(url: URL(string: videoModel!.videoUrl)!)
            mediaPlayer.delegate = self
            mediaPlayer.drawable = self
            generateThumbnails()
        }
    }
    
    func playVideo()
    {
        if mediaPlayer.media != nil
        {
            mediaPlayer.play()
        }
    }
    
    func pauseVideo()
    {
        if mediaPlayer.media != nil && mediaPlayer.isPlaying
        {
            mediaPlayer.pause()
        }
    }
    
    func stopVideo()
    {
        if mediaPlayer.media != nil
        {
            mediaPlayer.stop()
        }
    }

    required init?(coder: NSCoder)
    {
      fatalError("init(coder:) has not been implemented")
    }

    override func layoutSubviews()
    {
      super.layoutSubviews()
    }
     
    func generateThumbnails()
    {
        if mediaPlayer.media != nil
        {
            let vlcMediaThumbnailer: VLCMediaThumbnailer = VLCMediaThumbnailer(media: mediaPlayer.media, andDelegate: self)
            vlcMediaThumbnailer.thumbnailWidth = videoModel!.thumbnailWidth
            vlcMediaThumbnailer.thumbnailHeight = videoModel!.thumbnailHeight
            vlcMediaThumbnailer.snapshotPosition = 0.5

            vlcMediaThumbnailer.fetchThumbnail()
        }
    }

    func mediaThumbnailerDidTimeOut(_ mediaThumbnailer: VLCMediaThumbnailer!)
    {
        print("failed generating thumbnail")
    }
    
    func mediaThumbnailer(_ mediaThumbnailer: VLCMediaThumbnailer!, didFinishThumbnail thumbnail: CGImage!)
    {
        print("got another thumbnail")
        if(thumbnail != nil)
        {
            let thumbnailUIImage = UIImage(cgImage: thumbnail)
            let image = Image(uiImage: thumbnailUIImage).renderingMode(.original)
            videoModel!.thumbnails.append(image)
        }
    }
}

结果：

Answer 2

大家下午好！

我尝试了自己的实现，但没有成功好几个小时，所以我看到了这篇文章。 总的来说，@Shaybc 提供的代码可以工作，但可以简化。

无论@Shaybc代码还是我的代码，我不明白为什么我不能生成指向不同位置的多个缩略图。

慢慢点击按钮会生成第一个缩略图，但其他缩略图会变黑。快速点击会使所有缩略图变黑。

如果有人有任何想法，我会接受！

import SwiftUI
import AVFoundation
import MobileVLCKit

struct VLCPlayerTestView: View
{
    let videoUrl: String = "https://upload.wikimedia.org/wikipedia/commons/transcoded/c/c0/Big_Buck_Bunny_4K.webm/Big_Buck_Bunny_4K.webm.480p.vp9.webm"
    @ObservedObject var container = ThumbnailerContainer()

    var body: some View
    {
        Button {
            container.generateThumbnail(urlString: videoUrl)
        } label: {
            Text("Generate Thumbnail")
        }
        ScrollView {
            VStack(spacing: 20)
            {
                ForEach(0..<container.thumbnails.count, id: \.self) { itemIndex in
                    container.thumbnails[itemIndex]
                        .resizable()
                        .aspectRatio(contentMode: .fill)
                }
            }
        }
    }
}

class ThumbnailerContainer: ObservableObject {
    @Published var thumbnailers: [Thumbnailer] = []
    @Published var thumbnails: [Image] = []

    func generateThumbnail(urlString: String) -> Void {
        let thumbnailer = Thumbnailer(container: self)
        thumbnailer.generateThumbnail(urlString: urlString)
        thumbnailers.append(thumbnailer)
    }
}

class Thumbnailer: VLCMediaThumbnailerDelegate, ObservableObject {
    @Published var container: ThumbnailerContainer

    init(container: ThumbnailerContainer) {
        self.container = container
    }
    
    func generateThumbnail(urlString: String)
    {
        let media = VLCMedia(url: URL(string: urlString)!)
        let vlcMediaThumbnailer: VLCMediaThumbnailer = VLCMediaThumbnailer(media: media, andDelegate: self)
        vlcMediaThumbnailer.thumbnailWidth = 400
        vlcMediaThumbnailer.thumbnailHeight = 225
        vlcMediaThumbnailer.snapshotPosition = Float.random(in: 0...1)

        print("Fetching thumbnail for position \(vlcMediaThumbnailer.snapshotPosition)")
        vlcMediaThumbnailer.fetchThumbnail()
    }

    func mediaThumbnailerDidTimeOut(_ mediaThumbnailer: VLCMediaThumbnailer!)
    {
        print("failed generating thumbnail")
    }

    func mediaThumbnailer(_ mediaThumbnailer: VLCMediaThumbnailer!, didFinishThumbnail thumbnail: CGImage!)
    {
        print("Got a thumbnail for position \(mediaThumbnailer.snapshotPosition)")
        let thumbnailUIImage = UIImage(cgImage: thumbnail)
        let image = Image(uiImage: thumbnailUIImage).renderingMode(.original)
        container.thumbnails.append(image)
    }
}