[Feature]: Add num samples to `ImageSeries` when external mode is used

[h-mayorquin]

What would you like to see added to PyNWB?

@bendichter
Here is the time alignment view of Neurosift from an nwbfile that contains an ImageSeries with external video:

It should be noticeable that the information of time duration is missing for the ImageSeries. The reason is that the length can be estimated when there are timestamps or when there is a staring_time, rate and crucially num_samples (data.shape[0]). But here, the later is missing.

It would be great to have this added to the schema. Note that the starting_frame is not enough to determine the number of frames available for a single ImageSeries in external mode.

Weakly related to this other issue where some guidelines were given:
NeurodataWithoutBorders/pynwb#1433

Is your feature request related to a problem?

No response

What solution would you like?

Adding num_samples in the schema for this object or modify the data attribute in the case of external series so shape[0] reflects the number of samples.

Do you have any interest in helping implement the feature?

Yes.

Code of Conduct

• I agree to follow this project's Code of Conduct
• Have you checked the Contributing document?
• Have you ensured this change was not already requested?

[oruebel]

I transferred the issue to the schema repo since this issue is about making changes to the schema

[h-mayorquin]

#543 same probably