revid/webcam.go: wrote implementations of Start, Stop and Read methods

revid/webcam.go

@@ -26,7 +26,12 @@ package revid
 
 import (
 	"errors"
+	"fmt"
 	"io"
+	"os/exec"
+	"strings"
+
+	"bitbucket.org/ausocean/utils/logger"
 )
 
 const (
@@ -48,6 +53,7 @@ type Webcam struct {
 	out io.ReadCloser
 	log Logger
 	cfg Config
+	cmd *exec.Cmd
 }
 
 func NewWebcam(l Logger) *Webcam {
@@ -78,3 +84,51 @@ func (w *Webcam) Set(c Config) error {
 	w.cfg = c
 	return multiError(errs)
 }
+
+func (w *Webcam) Start() error {
+	args := []string{
+		"-i", w.cfg.InputPath,
+		"-f", "h264",
+		"-r", fmt.Sprint(w.cfg.FrameRate),
+	}
+
+	br := w.cfg.Bitrate * 1000
+	args = append(args,
+		"-b:v", fmt.Sprint(br),
+		"-maxrate", fmt.Sprint(br),
+		"-bufsize", fmt.Sprint(br/2),
+		"-s", fmt.Sprintf("%dx%d", w.cfg.Width, w.cfg.Height),
+		"-",
+	)
+
+	w.log.Log(logger.Info, pkg+"ffmpeg args", "args", strings.Join(args, " "))
+	w.cmd = exec.Command("ffmpeg", args...)
+
+	var err error
+	w.out, err = w.cmd.StdoutPipe()
+	if err != nil {
+		return fmt.Errorf("failed to create pipe: %w", err)
+	}
+
+	err = w.cmd.Start()
+	if err != nil {
+		return fmt.Errorf("failed to start ffmpeg: %w", err)
+	}
+
+	return nil
+}
+
+func (w *Webcam) Stop() error {
+	if w.cmd == nil || w.cmd.Process == nil {
+		return errors.New("raspivid process was never started")
+	}
+	err := w.cmd.Process.Kill()
+	if err != nil {
+		return fmt.Errorf("could not kill raspivid process: %w", err)
+	}
+	return w.out.Close()
+}
+
+func (w *Webcam) Read(p []byte) (int, error) {
+	return w.out.Read(p)
+}