如何在 Exoplayer 上显示 HLS 嵌入字幕

如何使用 Exoplayer、ExoMedia 或其他播放器启用并选择 HLS 格式的 Vimeo 视频中嵌入的不同字幕？ 在 iOS 中，同一个视频已经提供了原生字幕选项，但在 Android 中我找不到实现它的方法。

我在这里的答案看起来很像this one https://stackoverflow.com/questions/45835562/quality-selector-for-exoplayer-2/45844705#45844705，所以你可能想先检查一下那个。

ExoPlayer 是您想要的 Android 库。显示字幕是一项艰巨的任务，但是demo app https://github.com/google/ExoPlayer因为该库拥有处理 HLS 视频所需的所有代码。更具体地说PlayerActivity https://github.com/google/ExoPlayer/blob/release-v2/demo/src/main/java/com/google/android/exoplayer2/demo/PlayerActivity.java班级。您可以在演示应用程序中转到 HLS ->“Apple 16x9 基本流”，该视频有大量字幕（又名“文本轨道”）。

只是为了简化他们的代码，以便它不依赖于助手（这样你就可以看到它是如何工作的just关于隐藏式字幕）我在下面编写/记录了他们的一些代码。

private static class ClosedCaptionManager {

    ClosedCaptionManager(MappingTrackSelector mappingTrackSelector, SimpleExoPlayer player) {
        this.player = player;
        this.trackSelector = mappingTrackSelector;
    }

    SimpleExoPlayer player;
    MappingTrackSelector trackSelector;

    // These two could be fields OR passed around
    int textTrackIndex;
    TrackGroupArray trackGroups;

    ArrayList<Pair<Integer, Integer>> pairTrackList = new ArrayList<>();

    private boolean checkAndSetClosedCaptions() {
        // This is the body of the logic  for see if there are even video tracks
        // It also does some field setting
        MappedTrackInfo mappedTrackInfo = trackSelector.getCurrentMappedTrackInfo();
        if (mappedTrackInfo == null) {
            return false;
        }
        for (int i = 0; i < mappedTrackInfo.length; i++) {
            trackGroups = mappedTrackInfo.getTrackGroups(i);
            if (trackGroups.length != 0) {
                switch (player.getRendererType(i)) {
                    case C.TRACK_TYPE_TEXT:
                        textTrackIndex = i;
                        return true;
                }
            }
        }
        return false;
    }

    private void buildTrackList() {
        // This next part is actually about getting the list.
        // Below you'd be building up items in a list. This just does
        // views directly, but you could just have a list of track names (with indexes)
        for (int groupIndex = 0; groupIndex < trackGroups.length; groupIndex++) {
            TrackGroup group = trackGroups.get(groupIndex);
            for (int trackIndex = 0; trackIndex < group.length; trackIndex++) {
                if (trackIndex == 0) {
                    // Beginning of a new set, the demo app adds a divider
                }
                //CheckedTextView trackView = ...; // The TextView to show in the list
                // The below points to a util which extracts the quality from the TrackGroup
                //trackView.setText(DemoUtil.buildTrackName(group.getFormat(trackIndex)));
                Log.e("Thing", DemoUtil.buildTrackName(group.getFormat(trackIndex)));
                pairTrackList.add(new Pair<>(groupIndex, trackIndex));
            }
        }
    }

    private void onTrackViewClick(Pair<Integer, Integer> trackPair) {
        // Assuming you tagged the view with the groupIndex and trackIndex, you
        // can build your override with that info.
        Pair<Integer, Integer> tag = trackPair;
        int groupIndex = tag.first;
        int trackIndex = tag.second;
        // This is the override you'd use for something that isn't adaptive.
        // `override = new SelectionOverride(FIXED_FACTORY, groupIndex, trackIndex);`
        // Otherwise they call their helper for adaptives (HLS/DASH), which roughly does:
        int[] tracks = getTracksAdding(new MappingTrackSelector.SelectionOverride(
                        new FixedTrackSelection.Factory(), groupIndex, trackIndex),
                trackIndex
        );
        TrackSelection.Factory factory = tracks.length == 1
                ? new FixedTrackSelection.Factory()
                : new AdaptiveTrackSelection.Factory(BANDWIDTH_METER);

        MappingTrackSelector.SelectionOverride override =
                new MappingTrackSelector.SelectionOverride(factory, groupIndex, tracks);

        // Then we actually set our override on the selector to switch the text track
        trackSelector.setSelectionOverride(textTrackIndex, trackGroups, override);
    }

    private static int[] getTracksAdding(MappingTrackSelector.SelectionOverride override, int addedTrack) {
        int[] tracks = override.tracks;
        tracks = Arrays.copyOf(tracks, tracks.length + 1);
        tracks[tracks.length - 1] = addedTrack;
        return tracks;
    }
}

然后，如果您将以下代码发布到其末尾initializePlayer()方法，您将了解这些部分如何组合在一起。

    final ClosedCaptionManager closedCaptionManager = new ClosedCaptionManager(trackSelector, player);

    new Handler().postDelayed(new Runnable() {
        @Override
        public void run() {
            boolean hasTracks = closedCaptionManager.checkAndSetClosedCaptions();
            if (hasTracks) {
                closedCaptionManager.buildTrackList();
                closedCaptionManager.onTrackViewClick(closedCaptionManager.pairTrackList.get(4));
            }
        }
    }, 2000);

上面的代码非常草率，但它至少应该能让您朝着正确的方向开始。我不建议使用所写的任何内容 - 它主要应该是为了了解不同的部分如何组合在一起。他们在演示应用程序中的内容要好一些，因为他们的代码对于不同的轨道选择类型非常可重用（因为您可以拥有视频、音频和文本轨道）。