Add basic live transcoding to webm

pkg/ffmpeg/encoder_transcode.go

@@ -1,5 +1,10 @@
 package ffmpeg
 
+import (
+	"io"
+	"os"
+)
+
 type TranscodeOptions struct {
 	OutputPath string
 }
@@ -20,3 +25,18 @@ func (e *Encoder) Transcode(probeResult VideoFile, options TranscodeOptions) {
 	}
 	_, _ = e.run(probeResult, args)
 }
+
+func (e *Encoder) StreamTranscode(probeResult VideoFile) (io.ReadCloser, *os.Process, error) {
+	args := []string{
+		"-i", probeResult.Path,
+		"-c:v", "libvpx-vp9",
+		"-vf", "scale=iw:-2",
+		"-deadline", "realtime",
+		"-cpu-used", "5",
+		"-crf", "30",
+		"-b:v", "0",
+		"-f", "webm",
+		"pipe:",
+	}
+	return e.stream(probeResult, args)
+}