Support Multiple Streams Per Camera Entity

[Spittie68]

Describe your request

Home Assistant's camera entity architecture currently supports only one stream source per camera entity. This limitation affects multiple integrations and forces users to create duplicate camera entities as a workaround.

Current Behavior:

Each camera entity can only expose one stream via the stream_source() method
The method returns a single URL string, not a list or dictionary of streams
Users must create multiple camera entities to access different streams (main/sub) from the same physical camera

Affected Integrations:

Foscam - Issue 

home-assistant/core#118815 - Can only configure main OR sub stream, not both
Reolink - Issue
home-assistant/core#89156 - Multi-lens cameras don't expose all available streams
Frigate (custom integration) - Users must duplicate camera definitions to access both detection and live streams
ONVIF - Users manually create multiple generic camera entries for the same device

Why the uncertainty?

i dont know if it a core thing or what it below to

Use cases

Modern IP cameras universally provide multiple simultaneous streams for different purposes:

Main stream (high resolution): For recording and detailed viewing (e.g., 2560×1920, 4K)
Sub stream (low resolution): For detection, thumbnails, and low-bandwidth viewing (e.g., 640×480, 720p)

Real-world scenario:
A user with 12 security cameras wants to:

Display a grid dashboard using sub-streams (low bandwidth, fast loading)
Click any camera to view HD popup with main stream (high quality, detailed view)
Use sub-stream for object detection (lower CPU usage, faster processing)
Record main stream for archival quality

Current Workaround

Users must create duplicate camera entities for each physical camera:

Example with Frigate:

go2rtc:
streams:
camera1_sub:
- rtsp://camera1:554/stream2 # Sub stream
camera1_main:
- rtsp://camera1:554/stream1 # Main stream

cameras:
camera1: # For detection and grid view
ffmpeg:
inputs:
- path: rtsp://127.0.0.1:8554/camera1_sub
roles: [detect]

camera1_hd: # For HD viewing
ffmpeg:
inputs:
- path: rtsp://127.0.0.1:8554/camera1_main
roles: [record]

Problems with this approach:

Doubles (or triples) the number of camera entities
Increases system resource usage (duplicate processing)
Creates confusion in the UI (which entity to use?)
Requires extensive manual configuration
Breaks the logical relationship between streams from the same device

What areas might this affect?

Camera models commonly affected:

Reolink (RLC-520A, RLC-810A, TrackMix, Duo series)
Foscam (all models with dual streams)
Hikvision (all modern IP cameras)
Dahua (all modern IP cameras)
Amcrest (all IP camera models)
Axis (multi-sensor cameras)
Virtually all modern IP security cameras

Integrations that would benefit:

Reolink (official)
Foscam (official)
ONVIF (official)
Generic Camera (official)
Frigate (custom, highly popular)
Blue Iris (custom)
UniFi Protect (custom)

Anything else?

i hope i have doing it the right way here :)