Function moq_encode_video_bitrate 

#[unsafe(no_mangle)]
pub extern "C" fn moq_encode_video_bitrate(
    producer: u32,
    bitrate: u64,
) -> i32

Retune a live encoder to bitrate bits per second, taking effect from roughly the next frame. No keyframe is forced, so this is cheap enough to drive from a congestion controller.

The configured bitrate is a ceiling on some backends (openh264 rejects a raise above the rate it opened at), so set bitrate to the highest you will ask for and adapt downwards from there.

When this encoder was published against a bandwidth allocator, the reservation and follower ceiling move with it, so a later grant cannot retune above this value.

Returns a negative code if this backend cannot retune while running. That is not fatal: the encoder keeps running at its current rate, so stop adapting rather than stop publishing.