only use vaapi when feature is enabled

[skip ci] no need

Cargo.toml

@@ -24,3 +24,4 @@ toml = { package = "basic-toml", version = "0.1.4" }
 [features]
 default = ["mem_limit"]
 mem_limit = []
+vaapi = []

README.md

@@ -0,0 +1,17 @@
+**ACHTUNG!** This repository might be mirrored at different places, but the main repository is and remains at [msrd0.dev/msrd0/render_video](https://msrd0.dev/msrd0/render_video). Please redirect all issues and pull requests there.
+
+# render_video
+
+This "script" is an extremely fancy wrapper around ffmpeg to cut/render videos for the [VideoAG](https://video.fsmpi.rwth-aachen.de) of the [Fachschaft I/1 der RWTH Aachen University](https://fsmpi.rwth-aachen.de).
+
+You can find a ready-to-use docker image at [`quay.io/msrd0/render_video`](https://quay.io/msrd0/render_video).
+
+## Features
+
+ - **Extract a single audio channel from stereo recording.** We use that with one of our cameras that supports plugging a lavalier microphone (mono source) into one channel of the stereo recording, and using the camera microphone (mono source) for the other channel of the stereo recording.
+ - **Cut away before/after the lecture.** We don't hit the start record button the exact time that the lecture starts, and don't hit the stop button exactly when the lecture ends, so we need to cut away those unwanted bits.
+ - **Fast-forward through _Tafelwischpausen_.** Sometimes docents still use blackboards and need to wipe those, which can be fast-forwarded by this tool.
+ - **Overlay questions from the audience.** Sometimes people in the audience have questions, and those are usually poorly understood on the lavalier microphones. Therefore you can subtitle these using the other microphones in the room that don't make it into the final video and have those overlayed.
+ - **Add intro and outro.** We add intro and outro slides at the start/end at all lectures, which this tool can do for you.
+ - **Add our logo watermark.** We add a logo watermark in the bottom right corner of all videos, which this tool can do for you.
+ - **Rescale to lower resolutions.** We usually published videos at different resolutions, and this tool can rescale your video for all resolutions you want.

src/render/ffmpeg.rs

@@ -322,7 +322,7 @@ impl Ffmpeg {
 
 		// initialise a vaapi device if one exists
 		let vaapi_device: PathBuf = "/dev/dri/renderD128".into();
-		let vaapi = vaapi_device.exists();
+		let vaapi = cfg!(feature = "vaapi") && vaapi_device.exists();
 		if vaapi && venc {
 			if vdec {
 				cmd.arg("-hwaccel").arg("vaapi");