now it's possible to set input and output frame rate

src/main/kotlin/V4l2Recorder.kt

@@ -9,14 +9,18 @@ import org.openrndr.ffmpeg.VideoWriterProfile
 /**
  * The recorder will use `ffmpeg` with `-f v4l2` option for recording. Can be used together with `v4l2loopback`.
  *
- * @param v4lDevice the v4l device used for recording, should be writeable.
- * @param pixelFormat `rgb24` by default, will make it compatible with many clients like Chrome browser
- * and use less CPU for transcoding. It can be also yuv420p, etc.
- * see ffmpeg pix_fmt documentation.
+ * @param v4lDevice the `v4l` device used for recording, should be writeable.
+ * @param pixelFormat `rgb24` by default, will make it compatible with many clients like Chrome browser
+ * and use less CPU for transcoding. It can be also yuv420p, etc.
+ * see ffmpeg pix_fmt documentation.
+ * @param inputFrameRate typically screen refresh rate.
+ * @param outputFrameRate output camera refresh rate
  */
 class V4l2Recorder(
  private val v4lDevice: String,
- private val pixelFormat: String = "rgb24"
+ private val pixelFormat: String = "rgb24",
+ private val inputFrameRate: Int = 60,
+ private val outputFrameRate: Double = 30.0
 ) : Extension {
 
  override var enabled: Boolean = true
@@ -32,10 +36,16 @@ class V4l2Recorder(
  videoWriter = VideoWriter.create()
  .profile(object: VideoWriterProfile() {
  override fun arguments(): Array<String> {
- return arrayOf("-vf", "vflip", "-pix_fmt", pixelFormat, "-f", "v4l2")
+ return arrayOf(
+ "-vf", "vflip",
+ "-pix_fmt", pixelFormat,
+ "-r", outputFrameRate.toBigDecimal().toPlainString(),
+ "-f", "v4l2"
+ )
  }
  })
  .size(program.width, program.height)
+ .frameRate(inputFrameRate)
  .output(v4lDevice)
  .start()
  }