We need to test a campaign therefore, we would like to add pictures and videos on the questionnaire
Where/how do you want to add them, please? Stand-alone or linked to questions?
Did you try a note with media option? See https://xlsform.org/en/#media.
In general, see https://docs.getodk.org/form-styling/#media.
You can add media attachments
audio to every single question (no matter what type of question it is) see the link above that @wroos provided. You can also do the same with choices in
select_multiple questions (so every single choice can have media attachments).
The last option is adding media files to
video questions as default answers then they also should be displayed in a form.
Hint: But it seems not to work with all appearance options of selects, e.g. drop-down, see https://community.kobotoolbox.org/t/dropdown-list-with-images/46160.