MediaRecorder BlobEvent timecode clarification

[bradisbell]

From: https://w3c.github.io/mediacapture-record/#dom-blobeventinit-timecode

timecode, of type DOMHighResTimeStamp, readonly
The difference between the timestamp of the first chunk in data and the timestamp of the first chunk in the first BlobEvent produced by this recorder as a DOMHighResTimeStamp [HR-TIME]. Note that the timecode in the first produced BlobEvent does not need to be zero.

I don't think I've ever fully understand this sentence. If this is the value of the timestamp of the first chunk in data, compared to the value of the first chunk in data of the first event produced by this recorder, and if this is the first event, how could the value of timecode not be zero 0?

I believe at some point in the past, timecode would actually start at zero 0 for the first event, and then subsequent dataavailable BlobEvent timecode could be used to determine the duration of recorded MediaStream data thus far. It seems that the current way is to note the first event's timecode and offset subsequent timecode events by that first event's timecode value to see how much time has passed. That's fine, but depends on the assumption that the first event's timecode is the zero relative to other events.

[handellm]

Hi @jan-ivar @yellowdoge - is there historical context for how the spec text was laid out? What use case is it meant to support?

[handellm]

Friendly ping on this topic.