Added documentation for time-lapse export (master)

docs/docs/configuration/record.md

@@ -161,6 +161,25 @@ Using Frigate UI, HomeAssistant, or MQTT, cameras can be automated to only recor
 
 The export page in the Frigate WebUI allows for exporting real time clips with a designated start and stop time as well as exporting a time-lapse for a designated start and stop time. These exports can take a while so it is important to leave the file until it is no longer in progress.
 
+### Time-lapse export
+
+When exporting a time-lapse the default speed-up is 25x with 30 FPS. This means that every 25 seconds of (real-time) recording is condensed into 1 second of time-lapse video (always without audio) with a smoothness of 30 FPS.
+To configure the speed-up factor, the frame rate and further custom settings, the configuration parameter `timelapse_args` can be used. The below configuration example would change the time-lapse speed to 60x (for fitting 1 hour of recording into 1 minute of time-lapse) with 25 FPS:
+
+```yaml
+record:
+  enabled: True
+  export:
+    timelapse_args: "-vf setpts=PTS/60 -r 25"
+```
+
+:::warning
+
+When using `ffmpeg.hwaccel_args: preset-vaapi` globally, the resulting file size is typically undesirably large.
+To get a reasonable file size nevertheless, the ffmpeg parameter `-qp n` can be utilized (where `n` stands for the value of the quantisation parameter). Values of around 30 have shown to provide a reasonable tradeoff between quality and file size.
+
+:::
+
 ## Syncing Recordings With Disk
 
 In some cases the recordings files may be deleted but Frigate will not know this has happened. Recordings sync can be enabled which will tell Frigate to check the file system and delete any db entries for files which don't exist.