Chromecast -如何区分主媒体和替代媒体与HLS媒体？

Question

目前，我在Chromecast上面临一个与交替音轨和文本音轨管理有关的问题。

我试图用相同的语言来区分媒体轨道(音频和文本)，但是角色不同。根据Cast的文档，我们可以通过roles属性来确定这一点：main和alternate、subtitle和caption。

但是，当使用多个媒体轨道加载HLS清单时，roles属性总是以未定义的形式返回，因此我们无法确定音频轨道的角色是主的还是备用的，也不能确定文本轨道的角色是字幕还是标题。加载破折号时不会发生此错误。

在HLS媒体中，是否有其他方法来识别音频轨道的角色是主要的还是替代的？在此之后，是否还有其他方法来识别HLS媒体中的文本轨道是字幕还是标题？

我已经创建了一个与这个问题相关的谷歌的IssueTracker杂志，但是我还没有收到任何关于这个问题的返回。

下面是这个问题的一个例子。所使用的清单有两个音频轨道，一个main和另一个alternate，以及两个文本轨道，一个是subtitle，另一个是caption。清单与HTTP Live流媒体第二版一致。

HLS

清单

#EXTM3U
#EXT-X-VERSION:4
(version=1.11.14-26090)

# AUDIO groups
#EXT-X-MEDIA:TYPE=AUDIO,GROUP-ID="audio-aacl-128",LANGUAGE="pt",NAME="Portuguese",DEFAULT=YES,AUTOSELECT=YES,CHANNELS="2",URI="9645657-tst007-manifest-audio_por=128000.m3u8"
#EXT-X-MEDIA:TYPE=AUDIO,GROUP-ID="audio-aacl-128",LANGUAGE="pt",NAME="Portuguese (describes-video)",AUTOSELECT=YES,CHARACTERISTICS="public.accessibility.describes-video",CHANNELS="2",URI="9645657-tst007-manifest-audio_por_1=128000.m3u8"

# SUBTITLES groups
#EXT-X-MEDIA:TYPE=SUBTITLES,GROUP-ID="textstream",LANGUAGE="pt",NAME="Portuguese (caption)",DEFAULT=YES,AUTOSELECT=YES,CHARACTERISTICS="public.accessibility.describes-spoken-dialog,public.accessibility.describes-music-and-sound",URI="9645657-tst007-manifest-textstream_por=1000.m3u8"

# variants
#EXT-X-STREAM-INF:BANDWIDTH=1294000,CODECS="mp4a.40.2,avc1.64001F",RESOLUTION=854x480,AUDIO="audio-aacl-128",SUBTITLES="textstream",CLOSED-CAPTIONS=NONE
9645657-tst007-manifest-video_por=1097000.m3u8

# keyframes
#EXT-X-I-FRAME-STREAM-INF:BANDWIDTH=146000,CODECS="avc1.64001F",RESOLUTION=854x480,URI="keyframes/9645657-tst007-manifest-video_por=1097000.m3u8"

音轨

# Calling Receiver.playerManager.AudioTracksManager.getTracks()
{
  {
    assocLanguage:undefined,
    customData: undefined,
    forced: undefined,
    isInband: undefined,
    language: "pt",
    name: "Português"› 
    roles: undefined,
    subtype: undefined,
    trackContentId: undefined,
    trackContentType: "audio/mp4",
    trackId: 2,
    type: "AUDIO"
  },
  {
    assocLanguage: undefined,
    customData: undefined,
    forced: undefined,
    isInband: undefined,
    language: "pt",
    name: "Português"› 
    roles: undefined,
    subtype: undefined,
    trackContentId: undefined,
    trackContentType: "audio/mp4",
    trackId: 3,
    type: "AUDIO"
  }
}

文本轨迹

# Calling Receiver.playerManager.TextTracksManager.getTracks() 
{
  {
    assocLanguage: null,
    customData: undefined,
    forced: false,
    isInband: undefined,
    language: "pt",
    name: "Português"› 
    roles: undefined,
    subtype: undefined,
    trackContentId: undefined,
    trackContentType: "text/vtt",
    trackId: 4,
    type: "TEXT"
  },
  {
    assocLanguage: null,
    customData: undefined,
    forced: false,
    isInband: undefined,
    language: "pt",
    name: "Português"› 
    roles: undefined,
    subtype: undefined,
    trackContentId: undefined,
    trackContentType: "text/vtt",
    trackId: 5,
    type: "TEXT"
  }
}

破折号

音轨

# Calling Receiver.playerManager.AudioTracksManager.getTracks() 
{
  {
    assocLanguage:undefined,
    customData: undefined,
    forced: undefined,
    isInband: undefined,
    language: "pt",
    name: "Português"› 
    roles: ["alternate"],
    subtype: undefined,
    trackContentId: undefined,
    trackContentType: "mp4a.40.2",
    trackId: 1,
    type: "AUDIO"
  },
  {
    assocLanguage: undefined,
    customData: undefined,
    forced: undefined,
    isInband: undefined,
    language: "pt",
    name: "Português"› 
    roles: ["main"],
    subtype: undefined,
    trackContentId: undefined,
    trackContentType: "mp4a.40.2",
    trackId: 2,
    type: "AUDIO"
  }
}

文本轨迹

# When calling Receiver.playerManager.TextTracksManager.getTracks() 
{
  {
    assocLanguage:undefined,
    customData: undefined,
    forced: undefined,
    isInband: undefined,
    language: "pt",
    name: "Português"› 
    roles: ["subtitle"],
    subtype: "SUBTITLE",
    trackContentId: undefined,
    trackContentType: "application/mp4",
    trackId: 3,
    type: "TEXT"
  },
  {
    assocLanguage: undefined,
    customData: undefined,
    forced: undefined,
    isInband: undefined,
    language: "pt",
    name: "Português"› 
    roles: ["caption", "subtitle"],
    subtype: "SUBTITLE",
    trackContentId: undefined,
    trackContentType: "application/mp4",
    trackId: 4,
    type: "TEXT"
  }
}

Answer 1

是的一切都很好。请让我来投。我们试着享受这个show.please