When you distirbute a Creative Commons licensed work, you must attribute all licencors who authored some component of the work (unless you have been forbidden to do so by some author(s)). Being a downstream recipient does not diminish that responsibility.
When a person makes a derivative of a CC-licensed work, the license requires that person to attribute the original author and note the new work as a devirative. The Creative Commons FAQ says:
How do I properly attribute material offered under a Creative Commons license?
[...] You must also indicate if you have modified the work—for example, if you have taken an excerpt, or cropped a photo. (For versions prior to 4.0, this is only required if you have created an adaptation by contributing your own creative material, but it is recommended even when not required.) It is not necessary to note trivial alterations, such as correcting a typo or changing a font size. Finally, you must retain an indication of previous modifications to the work.
Generally speaking, you have the power under copyright to control the production and distribution of derivatives of your works. By licensing your work under a Creative Commons license, you have graciously given up some of that control, but only if derivative works follow specific attribution requirements. When C distributes B's derivative of your work, C is still distributing a derivative your work, and is only allowed by you to do so when following the requirements of your license grant.
In practical terms, if what you suggest were true (i.e., C did not need to give attribution) then any two colluding individuals could trivially eliminate the upstream attribution requirement for derivative works. Suppose, for example, B actively hopes to avoid attributing you, and so recruited C to distribute B's video without your name on it. If such a scheme were possible, the upstream attribution requirement on derivative works would be uselessly flimsy.