Recording fixes (#24072)

* pin genai review frames to the main stream

* retain previews as long as either stream has recordings

* watch sub stream recording health separately from main

* reject record_sub on the same input as record and document the role

* derive recording paths from the cache segment timestamp

Recording paths carry one second of resolution, but since sub stream recording start times are resolved to fractional wall clock, anchored to the cache file mtime and chained to the previous segment's end. A stream cutting segments faster than once a second resolves consecutive segments into the same second, so two rows collide on the unique path index and the batch insert fails. The cache segment name is unique per camera stream and second by construction because ffmpeg names segments with strftime, so the recording path is now built from that timestamp while the row keeps the resolved start time. This also restores the path semantics from before sub stream recording, when start times came straight from the cache filename.

Nothing derives times from recording paths: playback offsets, stream switching, and export all use the row's start time, which is unchanged, and the recordings sync matches files by exact path string.

* keep the rest of a recording batch when one row conflicts

* only publish record_sub status when a sub stream is configured

* don't shadow camera_cfg when publishing empty cache streams

* back off restarts when a recording stream goes stale

* give the shared sub stream grace on any capture thread reset

* include segment details in recording discard warnings

docs/docs/configuration/cameras.md

@@ -83,11 +83,12 @@ A camera is enabled by default but can be disabled by using `enabled: False`. Ca
 
 Each role can only be assigned to one input per camera. The options for roles are as follows:
 
-| Role     | Description                                                                         |
-| -------- | ----------------------------------------------------------------------------------- |
-| `detect` | Main feed for object detection. [docs](object_detectors.md)                         |
-| `record` | Saves segments of the video feed based on configuration settings. [docs](record.md) |
-| `audio`  | Feed for audio based detection. [docs](audio_detectors.md)                          |
+| Role         | Description                                                                                                  |
+| ------------ | ------------------------------------------------------------------------------------------------------------ |
+| `detect`     | Main feed for object detection. [docs](object_detectors.md)                                                  |
+| `record`     | Saves segments of the video feed based on configuration settings. [docs](record.md)                          |
+| `record_sub` | Saves segments of a second, lower quality stream with its own retention. [docs](record.md#sub-stream-recording) |
+| `audio`      | Feed for audio based detection. [docs](audio_detectors.md)                                                   |
 
 <ConfigTabs>
 <TabItem value="ui">

docs/docs/configuration/record.md

@@ -280,7 +280,7 @@ This configuration will retain recording segments that overlap with alerts and d
 In addition to the main recording stream, Frigate can record a second, lower quality stream for each camera. This serves two purposes:
 
 - **Quality selection during playback**: A quality selector (`Auto`, `Original`, or `Low`) appears in History view for cameras with sub stream recording enabled. `Original` and `Low` play only that stream's recordings. Time ranges where the selected stream has no footage are skipped during playback, and the selector notes when the selected stream has no recordings at all in the viewed time range. With `Auto` (the default), playback prefers the original quality and automatically falls back to the low quality stream when the connection cannot keep up, or for time ranges where the original recordings have expired. The selector shows each stream's video codec and audio details beneath the options; footage recorded by older Frigate versions shows no details.
-- **Extended retention**: Sub stream recordings have their own retention settings, fully independent of the main recordings. By giving the low quality recordings a longer retention period, you can keep weeks or months of low quality history using a fraction of the storage, and that history remains playable after the main recordings expire. Playback falls back to the low quality recordings automatically, and the timeline shows a muted treatment for time ranges where only low quality footage remains.
+- **Extended retention**: Sub stream recordings have their own retention settings, fully independent of the main recordings. By giving the low quality recordings a longer retention period, you can keep weeks or months of low quality history using a fraction of the storage, and that history remains playable after the main recordings expire. Playback falls back to the low quality recordings automatically, and the timeline shows a muted treatment for time ranges where only low quality footage remains. Timeline previews are kept for as long as either stream still has recordings, so scrubbing works across the whole retained history.
 
 ### Configuring sub stream recording
 
@@ -427,7 +427,7 @@ This table covers only features that read recordings from disk. Tracked object s
 
 ### Trade-offs
 
-- Recording a second stream increases overall storage use. The increase is typically small relative to the main recordings, since the low quality stream is much smaller.
+- Recording a second stream increases overall storage use. The increase is typically small relative to the main recordings, since the low quality stream is much smaller. Both streams are cached before being written to disk, so cache use goes up as well. See [the `/tmp/cache` area is separate](#the-tmpcache-area-is-separate) if you start seeing `No space left on device` errors after enabling it.
 - The go2rtc transcode approach continuously encodes the low quality stream, which uses CPU or GPU resources. This cost only applies to the transcode path; recording the camera's native sub stream does not re-encode. See the [go2rtc hardware acceleration documentation](https://github.com/AlexxIT/go2rtc?tab=readme-ov-file#source-ffmpeg) for accelerating the transcode.
 - Many camera sub streams do not include audio. If the source stream has no audio, the low quality recordings will not have audio.
 - **Matching video codecs and audio settings between the two streams gives the smoothest playback.** When playback combines both qualities on one timeline (the default `Auto` behavior: for example original quality during events with low quality in between, or low quality history after the original recordings expire) and the streams use different video codecs or audio settings, for example H.265 on the main stream and H.264 on the sub stream, or 16 kHz audio on one and 8 kHz on the other, playback still works: Frigate inserts a decoder reset at each quality transition, which can cause a barely-perceptible pause there. Configuring both streams in the camera's firmware to use the same video codec, audio codec, and sample rate makes transitions fully seamless, and a mismatched audio sample rate can also be corrected with [sub stream output args](#sub-stream-output-args). If one stream has audio and the other does not, combined time ranges play **without audio**; selecting a single quality with the playback selector always keeps that stream's audio.

docs/docs/integrations/mqtt.md

@@ -304,7 +304,7 @@ Topic with current state of notifications. Published values are `ON` and `OFF`.
 
 ### `frigate/<camera_name>/status/<role>`
 
-Publishes the current health status of each role that is enabled (`audio`, `detect`, `record`). Possible values are:
+Publishes the current health status of each role that is enabled (`audio`, `detect`, `record`, `record_sub`). `record_sub` is only published for cameras with [sub stream recording](/configuration/record#sub-stream-recording) enabled, and is tracked separately from `record` so a healthy main stream can't hide a stalled sub stream. Possible values are:
 
 - `online`: Stream is running and being processed
 - `offline`: Stream is offline and is being restarted