Even if this were the problem (and I don’t think it is), it doesn’t matter. To us end users music shouldn’t play significantly louder than video on the same device. You shouldn’t need to frantically adjust the volume when switching to music from watching TV. Not to mention Apple TV already has a feature to normalize volume. This is simply something that Apple needs to fix with a firmware update, and if they care about Apple TV at all they will.
We’ll have to agree to disagree then because I’m almost certain that’s exactly why people are saying video is quiet. It’s not like HomePod is saying to itself “this is video so let’s play it quietly.” The source material dictates volume.
This isn’t even an ‘issue’ that’s unique to HomePod either. Like I said, I experience the same thing on my 5.1 setup with music vs video. The difference is that a receiver has a much larger amp and is generally attached to much larger speakers and gets around this by simply having the ability to get louder. HomePod is 8W and can only get so loud.
Apple could work around this by increasing the amplified output for given input signals. However, then they’d have potential hardware issues with pushing the amps higher than they were designed to go for volumes louder than the HomePod currently goes because it’s now going to play music even louder than it currently does. You’ll still end up with a volume disparity, but it would be able to be turned up loud enough for video.
Apple could use volume equalization (or combine that with the previous work around), but then you’re also compressing the dynamic range which is a hell of a drawback, especially for music and music is what it was designed for.