Video player displays `body` as title/hover-text even when `filename` is present

### Steps to reproduce

1. Send an video message (`m.video`) containing both `body` and `filename` (differing from each other).
2. View the message.

### Outcome

#### What did you expect?

The `filename` is the filename, and so should be displayed as the title of the video file (hover-text for the video area), while the `body` is the caption, and so should be displayed as a inline message (see [spec as of v1.16](https://spec.matrix.org/v1.16/client-server-api/#mvideo)).

#### What happened instead?

The `body` was displayed in both locations.

(This *does* seem to display correctly when the video message is quoted. It also displays correctly for `m.file` and `m.image`, but not for `m.audio` — see #31116.)

### Operating system

_No response_

### Browser information

_No response_

### URL for webapp

staging.element.io

### Application version

Element version: 1.12.3-rc.0

### Homeserver

_No response_

### Will you send logs?

No