[media-source] Multiple attachable/detachable SourceBuffers (#360)

dsilhavy has just created a new issue for https://github.com/w3c/media-source:

== Multiple attachable/detachable SourceBuffers ==
This issue is a follow-up on the discussion we had in the W3C Media and Entertainment IG calls. See also `Additional Information` below.

# Overview
MSE based media players initialize the required `SourceBuffer` objects at the beginning of a media playback session. Currently, only one `SourceBuffer` per media type (e.g. `audio`,`video`) can be attached and used. 

# Description / Background / Use Cases

## Server-guided ad-insertion
In the context of server-guided ad-insertion a media player is temporarily switching playback between different content/manifest files (switch from main content to an ad and back). In this case, segments of different content might not be aligned perfectly:

<img width="404" alt="Screenshot 2025-01-08 at 15 23 19" src="https://github.com/user-attachments/assets/7317021e-35dd-47f8-9590-273ec1b1a21a" />

In the example above, segment 2 is not aligned with segment 1, both would overlap in the buffer. As a consequence, segment 1 needs to be played until the end before segment 2 can be appended to the `SourceBuffer`. In such cases, a virtual buffer can be maintained on a client, but appended segments there will not be parsed. In addition, the timing when to push from the virtual buffer to the main buffer can be tricky. 

# Suggested Solution
Having the possibility to maintain multiple `SourceBuffers` that can be detached and switched would make it easier for a media player to cover scenarios as the one described above. See also #359 for details on dynamically adding and removing `SourceBuffers`. 

# Additional Information
For related information, please refer to the meeting minutes of the W3C Media and Entertainment IG:

* [Joint meeting W3C/SVTA](https://www.w3.org/2024/12/10-me-minutes.html)
* [MEIG Monthly Meeting - 2025/01/07](https://www.w3.org/2025/01/07-me-minutes.html)

Please view or discuss this issue at https://github.com/w3c/media-source/issues/360 using your GitHub account


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Received on Wednesday, 8 January 2025 14:28:42 UTC