77 lines
2.6 KiB
Go
77 lines
2.6 KiB
Go
package service
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import (
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"context"
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"errors"
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"fmt"
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"os"
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"os/exec"
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"path/filepath"
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"strings"
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)
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// lastFrameSuffix marks a video's FULL-RESOLUTION last-frame still
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// ("u/x.mp4" → "u/x.mp4.last.jpg"). The 画图台 uses it as the 首帧 reference
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// when continuing a video (首尾帧 models); the first-frame THUMBNAIL reuses
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// thumbSuffix so list views load videos and images the same way.
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const lastFrameSuffix = ".last.jpg"
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// LastFrameKey returns the last-frame object key for a video key, and
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// IsLastFrameKey reports whether name refers to such a derived object.
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func LastFrameKey(rel string) string { return rel + lastFrameSuffix }
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func IsLastFrameKey(name string) bool { return strings.HasSuffix(name, lastFrameSuffix) }
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func LastFrameOrigKey(name string) string { return strings.TrimSuffix(name, lastFrameSuffix) }
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// extractVideoFrames pulls two stills from an mp4 via ffmpeg: the FIRST frame
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// downscaled for list thumbnails (≤thumbMaxDim) and the LAST frame at full
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// resolution. Callers treat this as best-effort — any missing ffmpeg or decode
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// failure just means the derived objects aren't stored.
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func extractVideoFrames(ctx context.Context, video []byte) (thumb, last []byte, err error) {
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ffmpeg, err := exec.LookPath("ffmpeg")
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if err != nil {
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return nil, nil, errors.New("ffmpeg not installed")
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}
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dir, err := os.MkdirTemp("", "vidframes-*")
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if err != nil {
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return nil, nil, err
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}
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defer os.RemoveAll(dir)
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in := filepath.Join(dir, "in.mp4")
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if err := os.WriteFile(in, video, 0o600); err != nil {
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return nil, nil, err
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}
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thumbPath := filepath.Join(dir, "thumb.jpg")
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if out, err := exec.CommandContext(ctx, ffmpeg, "-y", "-i", in,
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"-vf", fmt.Sprintf("scale='min(%d,iw)':-2", thumbMaxDim),
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"-frames:v", "1", "-q:v", "4", thumbPath).CombinedOutput(); err != nil {
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return nil, nil, fmt.Errorf("ffmpeg first frame: %v: %s", err, clipTail(out))
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}
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thumb, err = os.ReadFile(thumbPath)
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if err != nil {
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return nil, nil, err
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}
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// -sseof seeks from the end; a tiny negative offset lands on the final
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// frame(s). Some encodes have sparse keyframes near EOF, so fall back to a
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// wider window before giving up (thumb alone is still useful).
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lastPath := filepath.Join(dir, "last.jpg")
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for _, off := range []string{"-0.1", "-1"} {
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_ = exec.CommandContext(ctx, ffmpeg, "-y", "-sseof", off, "-i", in,
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"-frames:v", "1", "-q:v", "2", "-update", "1", lastPath).Run()
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if b, rerr := os.ReadFile(lastPath); rerr == nil && len(b) > 0 {
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last = b
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break
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}
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}
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return thumb, last, nil
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}
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func clipTail(b []byte) string {
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s := strings.TrimSpace(string(b))
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if len(s) > 300 {
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s = s[len(s)-300:]
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}
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return s
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}
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