I look forward to watching that video, I have trouble with this as well. Hip flexors and quads are painfully tight for me, and my bendy back compensates, but that only works in certain moves. I've recently picked up a few awesome stretches and exercises for this, mostly from the contortion coach at my studio (the infamous Sofia Vanezetti) that are really working for me right now (like a ton!!)
One is to go into the frogger stretch, and one at a time try to lift each leg up and point the foot at the ceiling, which rotates that side's hip down toward the floor and in the process rolls "across" the hip flexor in a way that feels awesome for me and loosens them up better than straight up and down hip flexor exercises (like pulsing up and down in a lunge) which can tend to make them tense up on me because they're so overly tight right now.
Another is to simply do a regular lunge, but turn the front foot outward (back foot still pointed straight back) and press forward into the lunge with that front foot turned out for a super deep stretch in the hip flexor. That simple rotation changes the way you're stretching the front hip to focus the stretch more specifically on the back hip flexor. (Got that one from my 14 year old cousin who does competitive gymnastics and who is so bendy she makes me look like a board lol)
Another is to lay flat on your back, tuck one foot under your butt so you're laying on your shin, you can keep the other up on the foot...the less arch in the back, the deeper the stretch. This one is more intense on the quad than the hip flexor but both are a problem for me. It's like when you're doing the basic standing quad stretch and you pull your foot back to your butt, but when you lay it down it gets much more intense.
If you're having a hard time visualizing any of those I could make a short video. Sorry if you included any of that in your vid veena, I haven't had a chance to watch it yet. Just wanted to kick in a couple things that are really helping me a lot right now.