Fix init value for storeLastSettings

[minhui-foxtel]

Hi here,
If streaming.lastMediaSettingsCachingInfo.enabled is disabled, from my understanding, dash.js should not take last selected track into account.
But from current implementation, if a a track set by MediaPlayer.setCurrentTrack(), it will be treated as lastSelectedTrack, see L209

dash.js/src/streaming/controllers/MediaController.js

Line 209 in 2ed7239

lastSelectedTracks[type] = settings;

then it will affect which track will be selected, see L64

dash.js/src/streaming/controllers/MediaController.js

Lines 63 to 65 in 2ed7239

	function setInitialMediaSettingsForType(type, streamInfo) {
	let settings = lastSelectedTracks[type] || getInitialSettings(type);
	const tracksForType = getTracksFor(type, streamInfo.id);

So need to get a way to avoid to set lastSelectedTrack when streaming.lastMediaSettingsCachingInfo is disabled. storeLastSettings seems to be a proper flag, see L194, but storeLastSettings of a track is hardcoded to true and never changed. This PR is to respect streaming.lastMediaSettingsCachingInfo.enabled and give a reasonable initial value.

dash.js/src/streaming/controllers/MediaController.js

Lines 190 to 194 in 2ed7239

	if (!noSettingsSave) {
	let settings = extractSettings(track);
	if (!settings || !tracks[id][type].storeLastSettings) return;

[minhui-foxtel]

selectInitialTrack has only 2 arguments, maybe it's for other purposes, but it doesn't take any effects at the moment.

[dsilhavy]

@minhui-foxtel i think the idea behind lastMediaSettingsCachingInfo.enabled is to enable/disable the usage of settings that are stored in the local storage.

What is the exact order of calls that causes a problem for you here? attachSource should reset lastSelectedTracks. Are you using a multiperiod MPD?

[minhui-foxtel]

@dsilhavy yep, I'm using multi period MPD, so no proper reason to call attachSource for the case.
Let me explain why I'd like to do this. I'm facing an incompatible audio codec issue when switch period. Let's see, there are two periods,

[
    { // Period 1
        audioTracks: [
            {
                codec: 'ec-3',
                audioChannelConfiguration: [2],
            },
            {
                codec: 'mp4a.40.2',
                audioChannelConfiguration: [2],
            },
        ],
    },
    { // Period 2
        audioTracks: [
            {
                codec: 'ec-3',
                audioChannelConfiguration: ['F801'],
            },
            {
                codec: 'mp4a.40.2',
                audioChannelConfiguration: [2],
            },
        ],
    },
];

If set audio track with ec-3 in Period 1, dash.js will use a different codec of track mp4a.40.2 for Period 2 since its audioChannelConfiguration [2] are the same as last selected track. see L85

dash.js/src/streaming/controllers/MediaController.js

Lines 75 to 86 in 2ed7239

	if (settings) {
	tracks = Array.from(tracksForType);
	tracks = filterTracksBySettings(tracks, matchSettingsLang, settings);
	tracks = filterTracksBySettings(tracks, matchSettingsIndex, settings);
	tracks = filterTracksBySettings(tracks, matchSettingsViewPoint, settings);
	if (!(type === Constants.AUDIO && !!lastSelectedTracks[type])) {
	tracks = filterTracksBySettings(tracks, matchSettingsRole, settings);
	}
	tracks = filterTracksBySettings(tracks, matchSettingsAccessibility, settings);
	tracks = filterTracksBySettings(tracks, matchSettingsAudioChannelConfig, settings);
	}

But it will cause playback stall on some CTV devices, e.g. Samsung. It's probably due to incompatible codec, but I'm not very sure so far, I've checked if use the track with the same codec, playback will go well.
So I tend to select initial track by myself, setCustomInitialTrackSelectionFunction seems to be a good choice, in order to let dash.js hit the custom function, I have to avoid dash.js to get the value form lastSelectedTracks[type] || getInitialSettings(type). see

dash.js/src/streaming/controllers/MediaController.js

Lines 63 to 65 in 2ed7239

	function setInitialMediaSettingsForType(type, streamInfo) {
	let settings = lastSelectedTracks[type] || getInitialSettings(type);
	const tracksForType = getTracksFor(type, streamInfo.id);

To achieve the goal, I disabled lastMediaSettingsCachingInfo.enabled and avoided to call mediaPlayer.setInitialMediaSettingsFor(), and it did work well. but if I select a track manually by mediaPlayer.setCurrentTrack(newTrack), the newTrack will be treated as last selected track, CustomInitialTrackSelectionFunction will not be called anymore. Adding an extra argument noSettingsSave to setCurrentTrack to prevent from saving the track as last selected track could also work around my issue.

function setCurrentTrack(track, noSettingsSave) {
    if (!streamingInitialized) {
        throw STREAMING_NOT_INITIALIZED_ERROR;
    }
    mediaController.setTrack(track, noSettingsSave);
}

But I think dash.js should have a way to prevent from setting last selected track.

Here's my code snippet,

const player = dashjs.MediaPlayer().create();
player.initialize(videoElement)
player.attachSource(source, startTime);

player.setCustomInitialTrackSelectionFunction(
    myTrackSelectionFunction
);

player.updateSettings({
    streaming: {
        lastMediaSettingsCachingInfo: {
            // dash.js takes `audioChannelConfiguration` into account but doesn't consider codec, 
            // so disable this and use `setCustomInitialTrackSelectionFunction` instead.
            enabled: false,
        },
    }
});

// Manually trigger this during Period 1, the newTrack will be set to last selected track, I need a way to prevent it.
player.setCurrentTrack(newTrack);

[dsilhavy]

Thanks for the detailed explanation. I would like to separate the logic for getting media settings from the local storage and saving the settings for a single streaming session.

1. Let's add the noSettingsSave flag to Mediaplayer.setCurrentTrack as in your example above.
2. If required, I suggest we introduce an additional settings flag like saveLastMediaSettingsForCurrentStreamingSession that enables/disables storeLastSettings as in your original PR

Does that work for you?

[minhui-foxtel]

@dsilhavy Thanks for your help, can you please review the PR again? Here's updates:

1. Added noSettingsSave flag to Mediaplayer.setCurrentTrack
2. I still think a settings flag to enable/disable storeLastSettings is needed since there are still other ways to set lastSelectedTracks, e.g. select a track by initial settings or settings from local storage. So added this flag in the PR as well.

[dsilhavy]

@dsilhavy Thanks for your help, can you please review the PR again? Here's updates:

1. Added noSettingsSave flag to Mediaplayer.setCurrentTrack
2. I still think a settings flag to enable/disable storeLastSettings is needed since there are still other ways to set lastSelectedTracks, e.g. select a track by initial settings or settings from local storage. So added this flag in the PR as well.

Thanks your PR looks good to me. Minor comments: Please add the following to index.d.ts

• the new setting saveLastMediaSettingsForCurrentStreamingSession
• the missing noSettingsSave to setCurrentTrack

[minhui-foxtel]

Updated index.d.ts @dsilhavy