examples/video: put a video file in a separate server

This change also fixes an issue where a file could be closed before
the video play ends.

Closes #3116

examples/video/main.go

@@ -15,21 +15,24 @@
 package main
 
 import (
-	"bufio"
-	"bytes"
 	_ "embed"
 	"fmt"
 	"io"
 	"log"
+	"net/http"
 	"os"
 
 	"github.com/hajimehoshi/ebiten/v2"
 	"github.com/hajimehoshi/ebiten/v2/audio"
 	"github.com/hajimehoshi/ebiten/v2/ebitenutil"
 )
 
-//go:embed shibuya.mpg
-var shibuya_mpg []byte
+// mpgURL is a URL of an example MPEG-1 video. The license is the following:
+//
+// https://commons.wikimedia.org/wiki/File:Shibuya_Crossing,_Tokyo,_Japan_(video).webm
+// "Shibuya Crossing, Tokyo, Japan (video).webm" by Basile Morin
+// The Creative Commons Attribution-Share Alike 4.0 International license
+const mpgURL = "https://example-resources.ebitengine.org/shibuya.mpg"
 
 type Game struct {
 	player *mpegPlayer
@@ -67,22 +70,23 @@ func main() {
 	//     ffmpeg -i YOUR_VIDEO -c:v mpeg1video -q:v 8 -c:a mp2 -format mpeg -ar 48000 output.mpg
 	//
 	// You can adjust quality by changing -q:v value. A lower value indicates better quality.
-	var in io.ReadSeeker
+	var in io.ReadCloser
 	if len(os.Args) > 1 {
 		f, err := os.Open(os.Args[1])
 		if err != nil {
 			log.Fatal(err)
 		}
-		defer func() {
-			_ = f.Close()
-		}()
 		in = f
 	} else {
-		in = bytes.NewReader(shibuya_mpg)
+		res, err := http.Get(mpgURL)
+		if err != nil {
+			log.Fatal(err)
+		}
+		in = res.Body
 		fmt.Println("Play the default video. You can specify a video file as an argument.")
 	}
 
-	player, err := newMPEGPlayer(bufio.NewReader(in))
+	player, err := newMPEGPlayer(in)
 	if err != nil {
 		log.Fatal(err)
 	}

examples/video/mpegplayer.go

@@ -50,10 +50,14 @@ type mpegPlayer struct {
 	// These members are used when the video doesn't have an audio stream.
 	refTime time.Time
 
+	src io.ReadCloser
+
+	closeOnce sync.Once
+
 	m sync.Mutex
 }
 
-func newMPEGPlayer(src io.Reader) (*mpegPlayer, error) {
+func newMPEGPlayer(src io.ReadCloser) (*mpegPlayer, error) {
 	mpg, err := mpeg.New(src)
 	if err != nil {
 		return nil, err
@@ -70,6 +74,7 @@ func newMPEGPlayer(src io.Reader) (*mpegPlayer, error) {
 		yCbCrImage: ebiten.NewImage(mpg.Width(), mpg.Height()),
 		yCbCrBytes: make([]byte, 4*mpg.Width()*mpg.Height()),
 		frameImage: ebiten.NewImage(mpg.Width(), mpg.Height()),
+		src:        src,
 	}
 
 	s, err := ebiten.NewShader([]byte(`package main
@@ -140,7 +145,14 @@ func (p *mpegPlayer) updateFrame() error {
 	video := p.mpg.Video()
 	if video.HasEnded() {
 		p.frameImage.Clear()
-		return nil
+		var err error
+		p.closeOnce.Do(func() {
+			fmt.Println("The video has ended.")
+			if err1 := p.src.Close(); err1 != nil {
+				err = err1
+			}
+		})
+		return err
 	}
 
 	d := 1 / p.mpg.Framerate()