First thing that caught my attention is the claim the video was shot over the South China Sea. Lots of military intrigue there from multiple nations.
I'm fairly confident these are anti-missile flares being dropped by multiple military aircraft, likely smallish fighters. They probably aren't visible due to their distance from the commercial jet and their tactical gray color blending with the gray clouds.
It took me a while to find a video of a military a/c dropping flares that replicates what we see on the video. Notice both the pattern and burn time compared to the South China Sea video.