我正在使用m3u8视频格式来流式传输视频,现在需要显示相应的字幕。
我在苹果文档中搜索到了使用AVPlayer
的closedCaptionDisplayEnabled
属性可以实现此功能。
我想知道字幕的格式应该是什么?使用.srt格式是否可行?
同时,我能否使用MPMoviePlayerController
来实现同样的功能?
任何帮助都将不胜感激。
我正在使用m3u8视频格式来流式传输视频,现在需要显示相应的字幕。
我在苹果文档中搜索到了使用AVPlayer
的closedCaptionDisplayEnabled
属性可以实现此功能。
我想知道字幕的格式应该是什么?使用.srt格式是否可行?
同时,我能否使用MPMoviePlayerController
来实现同样的功能?
任何帮助都将不胜感激。
更新于03/06/2020: 在 GitHub 上,jbweimar 创建了一个使用 AVAssetResourceLoaderDelegate
方法的示例项目,看起来非常有前途:https://github.com/jbweimar/external-webvtt-example
更新于10/30/2018: 值得注意的是查看苹果工程师的这个答案(感谢@allenlini提供的提示)。
他建议采用涉及 AVAssetResourceLoaderDelegate
的解决方案。我自己没有尝试过,但它可能比下面我的解决方案更好。
原始回答:
似乎在 m3u8 流描述中引用 WebVTT 文件是官方支持的方式。事实上,在后期添加它们似乎不受官方支持(请参见一位苹果工程师在本页底部发表的声明)。
然而,这并不意味着你不能让它工作 ;-)。借助这个精彩的演示文稿和 Chris Adamson 的示例项目(ZIP),苹果开发者论坛上的这篇帖子以及 Abdul Azeem 的这篇 Ray Wenderlich 教程,我成功地让它工作了。这是 Abdul Azeem 示例代码和 Chris 的示例项目的修改版本。
请注意,需要使用 AVMediaTypeText
而不是 AVMediaTypeSubtitle
。这似乎是 iOS 中的一个错误。
// 1 - Load video asset
AVAsset *videoAsset = [AVURLAsset assetWithURL:[[NSBundle mainBundle] URLForResource:@"video" withExtension:@"mp4"]];
// 2 - Create AVMutableComposition object. This object will hold your AVMutableCompositionTrack instances.
AVMutableComposition *mixComposition = [[AVMutableComposition alloc] init];
// 3 - Video track
AVMutableCompositionTrack *videoTrack = [mixComposition addMutableTrackWithMediaType:AVMediaTypeVideo
preferredTrackID:kCMPersistentTrackID_Invalid];
[videoTrack insertTimeRange:CMTimeRangeMake(kCMTimeZero, videoAsset.duration)
ofTrack:[[videoAsset tracksWithMediaType:AVMediaTypeVideo] objectAtIndex:0]
atTime:kCMTimeZero error:nil];
// 4 - Subtitle track
AVURLAsset *subtitleAsset = [AVURLAsset assetWithURL:[[NSBundle mainBundle] URLForResource:@"subtitles" withExtension:@"vtt"]];
AVMutableCompositionTrack *subtitleTrack = [mixComposition addMutableTrackWithMediaType:AVMediaTypeText
preferredTrackID:kCMPersistentTrackID_Invalid];
[subtitleTrack insertTimeRange:CMTimeRangeMake(kCMTimeZero, videoAsset.duration)
ofTrack:[[subtitleAsset tracksWithMediaType:AVMediaTypeText] objectAtIndex:0]
atTime:kCMTimeZero error:nil];
// 5 - Set up player
AVPlayer *player = [AVPlayer playerWithPlayerItem: [AVPlayerItem playerItemWithAsset:mixComposition]];
这是@JohannesFahrenkrug的答案的Swift版本。希望对某些人有用:
let localVideoAsset = Bundle.main.url(forResource: "L1C1P1C3", withExtension: "mp4")
//Create AVMutableComposition
let videoPlusSubtitles = AVMutableComposition()
//Adds video track
let videoTrack = videoPlusSubtitles.addMutableTrack(withMediaType: .video, preferredTrackID: kCMPersistentTrackID_Invalid)
try? videoTrack?.insertTimeRange(CMTimeRangeMake(kCMTimeZero, localVideoAsset.duration),
of: localVideoAsset.tracks(withMediaType: .video)[0],
at: kCMTimeZero)
//Adds subtitle track
let subtitleAsset = AVURLAsset(url: Bundle.main.url(forResource: "L1C1P1C3", withExtension: ".mp4.vtt")!)
let subtitleTrack = videoPlusSubtitles.addMutableTrack(withMediaType: .text, preferredTrackID: kCMPersistentTrackID_Invalid)
try? subtitleTrack?.insertTimeRange(CMTimeRangeMake(kCMTimeZero, localVideoAsset.duration),
of: subtitleAsset.tracks(withMediaType: .text)[0],
at: kCMTimeZero)
添加字幕时出现音频错误。更新版本如下;
注意:仅支持将本地项目(资产)插入到AVMutableComposition中,在iOS 15之前,无法使用远程项目(例如HTTP视频流)。
将HTTP流插入到AVMutableComposition中
Swift 5
func play() {
guard let videoUrl = Bundle.main.url(forResource: "ElephantsDream", withExtension: "mp4")?.absoluteURL,
let subtitleUrl = Bundle.main.url(forResource: "subtitles-en", withExtension: "vtt")?.absoluteURL else {
return
}
let videoAsset = AVURLAsset(url: videoUrl)
let subtitleAsset = AVURLAsset(url: subtitleUrl)
// Create AVMutableComposition object. This object will hold your AVMutableCompositionTrack instances.
let mixComposition = AVMutableComposition()
let videoTrack = mixComposition.addMutableTrack(withMediaType: .video, preferredTrackID: kCMPersistentTrackID_Invalid)
let audioTrack = mixComposition.addMutableTrack(withMediaType: .audio, preferredTrackID: kCMPersistentTrackID_Invalid)
let subtitleTrack = mixComposition.addMutableTrack(withMediaType: .text, preferredTrackID: kCMPersistentTrackID_Invalid)
do {
try videoTrack?.insertTimeRange(CMTimeRangeMake(start: .zero, duration: videoAsset.duration),
of: videoAsset.tracks(withMediaType: .video).first!,
at: .zero)
try audioTrack?.insertTimeRange(CMTimeRangeMake(start: .zero, duration: videoAsset.duration),
of: videoAsset.tracks(withMediaType: .audio).first!,
at: .zero)
try subtitleTrack?.insertTimeRange(CMTimeRangeMake(start: .zero, duration: subtitleAsset.duration),
of: subtitleAsset.tracks(withMediaType: .text).first!, at: .zero)
} catch let err {
print(err.localizedDescription)
}
let player = AVPlayer(playerItem: AVPlayerItem(asset: mixComposition))
let vc = AVPlayerViewController()
vc.player = player
present(vc, animated: true) {
vc.player?.play()
}
}
func play() {
if #available(iOS 15.0.0, *) {
let videoUrl = URL(string: "https://wwww.acme.com/video/elephantsdream.mov")!
let subtitleUrl = URL(string: "https://wwww.acme.com/subtitle/subtitles-en.vtt")!
let videoAsset = AVURLAsset(url: videoUrl)
let subtitleAsset = AVURLAsset(url: subtitleUrl)
let mixComposition = AVMutableComposition()
let videoTrack = mixComposition.addMutableTrack(withMediaType: .video, preferredTrackID: kCMPersistentTrackID_Invalid)
let audioTrack = mixComposition.addMutableTrack(withMediaType: .audio, preferredTrackID: kCMPersistentTrackID_Invalid)
let subtitleTrack = mixComposition.addMutableTrack(withMediaType: .text, preferredTrackID: kCMPersistentTrackID_Invalid)
Task {
if let videoTrackItem = try await videoAsset.loadTracks(withMediaType: .video).first {
try videoTrack?.insertTimeRange(CMTimeRangeMake(start: .zero, duration: videoAsset.duration),
of: videoTrackItem,
at: .zero)
}
if let audioTrackItem = try await videoAsset.loadTracks(withMediaType: .audio).first {
try audioTrack?.insertTimeRange(CMTimeRangeMake(start: .zero, duration: videoAsset.duration),
of: audioTrackItem,
at: .zero)
}
if let subtitleTrackItem = try await subtitleAsset.loadTracks(withMediaType: .text).first {
try subtitleTrack?.insertTimeRange(CMTimeRangeMake(start: .zero, duration: videoAsset.duration),
of: subtitleTrackItem,
at: .zero)
}
DispatchQueue.main.async {
let player = AVPlayer(playerItem: AVPlayerItem(asset: mixComposition))
let vc = AVPlayerViewController()
vc.player = player
self.present(vc, animated: true) {
vc.player?.play()
}
}
}
}
}
AVPlayer和MPMoviePlayerController都可以显示字幕。
区别在于,使用AVPlayer时,您可以使用closedCaptionDisplayEnabled属性控制是否显示字幕。
而在MPMoviePlayerController中,用户可以通过设置应用程序中的开关来控制是否显示字幕。您无法在应用程序中进行编程控制。
closedCaptionDisplayEnabled
切换的是闭路字幕,而不是字幕。它们是两个不同的东西,该属性对字幕没有影响。(一个注意点:我只在 OS X 上尝试过这个,而没有在 iOS 上尝试过。) - Peter HoseyWWDC 2013 iOS应用程序使用WebVTT文件作为其字幕(感谢Nicholas Riley发现此问题)。由于某种原因,每个会话大约有50个(确切数字不同)。
我不知道AVFoundation或MPMoviePlayer级别是否支持WebVTT,或者应用程序是否下载并解析字幕文件。
快速搜索“webvtt m3u8”会出现对此HTTP Live Streaming Draft的引用,该草案建议您只需在m3u8播放列表中引用WebVTT文件即可使其正常工作。但是,我没有为您提供示例,因为我无法轻松猜测WWDC会话的m3u8 URL。
let videoAsset = AVURLAsset(url: videoUrl)
let subtitleAsset = AVURLAsset(url: subtitleUrl)
let mixComposition = AVMutableComposition()
let videoTrack = mixComposition.addMutableTrack(withMediaType: .video, preferredTrackID: kCMPersistentTrackID_Invalid)
let audioTrack = mixComposition.addMutableTrack(withMediaType: .audio, preferredTrackID: kCMPersistentTrackID_Invalid)
let subtitleTrack = mixComposition.addMutableTrack(withMediaType: .text, preferredTrackID: kCMPersistentTrackID_Invalid)
Task {
if let videoTrackItem = try await videoAsset.loadTracks(withMediaType: .video).first {
try await videoTrack?.insertTimeRange(CMTimeRangeMake(start: .zero, duration: videoAsset.load(.duration)),
of: videoTrackItem,
at: .zero)
}
if let audioTrackItem = try await videoAsset.loadTracks(withMediaType: .audio).first {
try await audioTrack?.insertTimeRange(CMTimeRangeMake(start: .zero, duration: videoAsset.load(.duration)),
of: audioTrackItem,
at: .zero)
}
if let subtitleTrackItem = try await subtitleAsset.loadTracks(withMediaType: .text).first {
try await subtitleTrack?.insertTimeRange(CMTimeRangeMake(start: .zero, duration: videoAsset.load(.duration)),
of: subtitleTrackItem,
at: .zero)
}
DispatchQueue.main.async {
let player = AVPlayer(playerItem: AVPlayerItem(asset: mixComposition))
let vc = AVPlayerViewController()
vc.player = player
self.present(vc, animated: true) {
vc.player?.play()
}
}
}
closedCaptionDisplayEnabled
“指示播放器是否使用闭路字幕”,并未提及任何关于字幕的内容。在我的测试中(在 OS X 上),该属性对字幕没有影响;它只适用于闭路字幕。(您可以通过使用 EyeTV 录制带有闭路字幕的电视节目,然后将其导出到 iPhone 和 MPEG-2 复合格式,最后使用 HandBrake 转换后进行自行测试。EyeTV 到 iPhone 的导出将具有 CC 轨道;HandBrake 转换后将具有字幕轨道。) - Peter Hosey