SGAI: alternative and list mpd

[cotid-qualabs]

Alternative MPD and List MPD implementation

[gemini-code-assist]

Summary of Changes

Hello @cotid-qualabs, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request significantly enhances the player's capabilities by integrating support for DASH Alternative Media Presentations and the List MPD profile. These additions enable advanced content manipulation, such as dynamic ad insertion, content replacement, and modular manifest composition, providing greater flexibility for content providers and a more dynamic viewing experience for users.

Highlights

• Alternative Media Presentation Support: Introduced comprehensive support for DASH Alternative Media Presentations, allowing dynamic switching between main and alternative content (e.g., ad insertion, content replacement). This includes new controllers (AlternativeMediaController, MediaManager) and event handling logic.
• List MPD Implementation: Added support for the List MPD profile, enabling manifests to reference external MPDs for individual periods. This allows for more flexible and modular manifest creation and dynamic period resolution.
• New Samples and Functional Tests: Included several new samples (list-mpds.html, alternative-media-presentations.html, live-to-live.html, listen-mode.html, sgai-insert-test.html) to demonstrate the new features. Corresponding functional tests have been added to ensure correct behavior for various scenarios like clipping, executeOnce, returnOffset, and status updates.
• Enhanced Event Handling: The EventController has been significantly updated to correctly process new attributes for Alternative MPD events, including earliestResolutionTimeOffset for pre-buffering, noJump for handling seek-ahead scenarios, and executeOnce for single-trigger events.
• Manifest Model and Adapter Updates: The DashManifestModel and DashAdapter were updated to parse and merge linked periods from external MPDs into the main manifest structure, ensuring seamless playback transitions.

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[gemini-code-assist]

Code Review

This pull request introduces significant new functionality for Alternative Media Presentations and List MPDs, which is a great addition. The implementation includes new controllers, models, and sample pages to demonstrate the features. The code is generally well-structured. I've found a few issues, including some duplicate event definitions in CoreEvents.js that should be addressed. I've also suggested some minor refactoring in the new sample pages for better maintainability. Overall, this is a solid contribution.

[gemini-code-assist]

These event definitions are duplicates of lines 62 and 64. Please remove them to avoid confusion and potential issues.

[gemini-code-assist]

This switch statement can be refactored into a more maintainable data structure, like a map or an object, to associate case IDs with their behavior descriptions. This will make the code cleaner and easier to extend with new cases.

                    const behaviors = {
                        'case0': "The player should download the Imported MPD and reproduce the unique Period.",
                        'case1': "The player should download the first Imported MPD, reproduce its first Period, and, upon completion, download the second Imported MPD and reproduce its first Period.",
                        'case2': "The player should download the first Imported MPD, reproduce its first Period, and, upon completion, play the next regular Period.",
                        'case3': "The player should start by playing the first regular Period as usual and, upon completion, download the linked Imported MPD and reproduce its first Period.",
                        'case4': "The player should start by playing the first regular Period as usual and, upon its completion, download the linked Imported MPD at startTime - earliestResolutionTime and reproduce its first Period",
                        'case5': "The player should start by playing the first regular Period as usual and, upon its completion, download the linked Imported MPD at with earliestResolutionTime = 0 and reproduce its first Period.",
                        'case6': "The player must respect the shortest duration between the Linked Period in the main manifest and the Imported MPD. Playback should seamlessly stop at the shorter duration, ensuring no content extends beyond the specified boundaries.",
                        'case7': "The player should throw an error indicating that the start time of the first period in a list type MPD manifest is invalid.",
                        'case8': "The player should attempt to download the manifest four times before failing."
                    };
                    if (behaviors[caseId]) {
                        behavior.innerText = behaviors[caseId];
                    }

[gemini-code-assist]

Consider using const instead of var for variables that are not reassigned. This is a modern JavaScript best practice that improves code clarity and prevents accidental reassignment.

Suggested change

	var video = document.getElementById('video-element');
	var alternativeVideo = document.getElementById('alternative-video-element');
	const video = document.getElementById('video-element');
	const alternativeVideo = document.getElementById('alternative-video-element');

[gemini-code-assist]

The manifestUrl parameter is passed to addManifestResponseInterceptor, but the function is defined without any parameters and does not use it. Please remove the unused parameter.

Suggested change

	addManifestResponseInterceptor(manifestUrl);
	addManifestResponseInterceptor();

[gemini-code-assist]

This line is a duplicate of the line above. Please remove it.