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// Package thumb generates thumbnail images.
package thumb
import (
"context"
"fmt"
"math/rand"
"os/exec"
"time"
)
// Generator creates a thumbnail for a given media file.
type Generator interface {
Generate(ctx context.Context, inputPath, outputPath string, duration float64) error
}
// FFmpegGenerator uses ffmpeg to extract a random frame.
type FFmpegGenerator struct {
execer func(ctx context.Context, name string, arg ...string) *exec.Cmd
rnd *rand.Rand
}
var _ Generator = (*FFmpegGenerator)(nil)
// NewFFmpegGenerator creates a new FFmpegGenerator with a seeded random source.
func NewFFmpegGenerator() *FFmpegGenerator {
return &FFmpegGenerator{
execer: exec.CommandContext,
rnd: rand.New(rand.NewSource(time.Now().UnixNano())),
}
}
const thumbWaitDelay = 15 * time.Second
// Generate picks a random offset (at least 1 second if duration > 0) and
// runs ffmpeg to produce a JPEG thumbnail.
func (g *FFmpegGenerator) Generate(ctx context.Context, inputPath, outputPath string, duration float64) error {
offset := 0.0
if duration > 0 {
offset = g.rnd.Float64() * duration
if offset < 1.0 {
offset = 1.0
}
}
// Build args: only add -ss when we have a real duration (video).
// For static images, -ss before -i produces no output frame on some
// ffmpeg versions (it skips past the single image2 frame).
args := []string{"-i", inputPath}
if duration > 0 {
// Prepend -ss before -i for fast seek when we have a video.
args = append([]string{"-ss", fmt.Sprintf("%.3f", offset)}, args...)
}
args = append(args,
"-vf", "scale=320:-1",
"-frames:v", "1",
"-q:v", "2",
"-y",
outputPath,
)
cmd := g.execer(ctx, "ffmpeg", args...)
cmd.WaitDelay = thumbWaitDelay
if err := cmd.Run(); err != nil {
return fmt.Errorf("ffmpeg generate thumbnail for %s: %w", inputPath, err)
}
return nil
}
// MockGenerator is a test fake for Generator.
type MockGenerator struct {
GenerateFunc func(ctx context.Context, inputPath, outputPath string, duration float64) error
}
// Generate delegates to GenerateFunc or succeeds silently.
func (m *MockGenerator) Generate(ctx context.Context, inputPath, outputPath string, duration float64) error {
if m.GenerateFunc != nil {
return m.GenerateFunc(ctx, inputPath, outputPath, duration)
}
return nil
}
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