not sure what you mean. He does not add a "d" sound. In fact he never settles on a specific pronunciation rather he shows the possibilities it can be (but none of them have a "d" sound). He appears to hint toward a like--pronunciation close to "YiH-YeH" as seen at 8:58 but in the end does not settle on a specific way to pronounce it. He does repeatedly say the names of the letters of the tetragram "Yod-He-Wa-He" but this only is the hebrew name of the letters rather than the pronunciation of the word and would be how a native Hebrew speaker would speak the letters (not the spelling of the letters put together). I'm not sure if you interpreted it this way but I don't think that is his intentions.
For further research on what Jeff Benner's thoughts (the youtube poster) on the subject he has a two part series discussing the Ex 3:14,15 (each about 8 min long)
The first video discusses verse 14 and second verse 15 (where the tetragram appears) and he does in fact give his opinion on what the pronunciation is in the second video (and it does not have a 'd' sound) at 2:08 as "
Yih'weh". He has a few reasons on why he settles on this but what I believe to be his main point is that in ancient Hebrew all Hebrew names were also Hebrew words with meaning. He shows that words like Jehovah, Yahweh, Yahueh, Yehovah, etc... mean nothing in Hebrew; they are not words and they have no meaning. He concludes from this that these common transliterations must be erroneous and this leads him settling on "
Yih'weh" as the pronunciation as a more practical and self-evident pronunciation based on how the language works.