视频变速

复制import subprocess
import os

# 使用 FFmpeg setpts 滤镜实现视频变速
input_file = "input.mp4"
output_file = "output_2x.mp4"
speed_factor = 2.0  # 2x 加速

# setpts: 视频时间戳缩放，PTS = 原PTS / speed_factor
# 音频需同步调整：atempo 滤镜（范围 0.5~2.0，超范围需级联）
filter_video = f"setpts={1/speed_factor}*PTS"
filter_audio = f"atempo={speed_factor}" if 0.5 <= speed_factor <= 2.0 else None

if filter_audio:
    cmd = [
        "ffmpeg", "-i", input_file,
        "-filter_complex", f"{filter_video};{filter_audio}",
        "-c:v", "libx264", "-c:a", "aac",
        output_file
    ]
else:
    # 超范围时只处理视频，音频静音或丢弃
    cmd = [
        "ffmpeg", "-i", input_file,
        "-vf", filter_video,
        "-an",  # 丢弃音频
        "-c:v", "libx264",
        output_file
    ]

subprocess.run(cmd, check=True)
print(f"生成 {output_file}")

复制package main

import (
	"fmt"
	"os/exec"
	"strconv"
)

func main() {
	input := "input.mp4"
	output := "output_0.5x.mp4"
	speed := 0.5 // 0.5x 慢放

	// setpts: PTS = PTS / speed，慢放时 speed<1 导致 PTS 增大
	pts := 1.0 / speed
	filter := fmt.Sprintf("setpts=%f*PTS", pts)

	// 音频 atempo 范围 0.5~2.0，0.5x 在范围内
	audioFilter := fmt.Sprintf("atempo=%f", speed)

	cmd := exec.Command("ffmpeg",
		"-i", input,
		"-filter_complex", filter+";"+audioFilter,
		"-c:v", "libx264",
		"-c:a", "aac",
		output,
	)

	if err := cmd.Run(); err != nil {
		panic(err)
	}
	fmt.Println("生成 " + output + "，速度 " + strconv.FormatFloat(speed, 'f', 2, 64) + "x")
}

复制// 纯前端模拟：用 Canvas 和 AudioContext 实现简单变速（非 FFmpeg）
// 实际工具使用 WASM FFmpeg，此处演示核心逻辑

function changeSpeed(videoUrl, speed, callback) {
  const video = document.createElement('video');
  video.src = videoUrl;
  video.onloadedmetadata = () => {
    // 设置 playbackRate 实现变速（0.25~4.0）
    video.playbackRate = speed;
    video.play();
    callback(null, video);
  };
  video.onerror = (e) => callback(e);
}

// 示例：2x 加速播放
changeSpeed('input.mp4', 2.0, (err, el) => {
  if (err) {
    console.error('加载失败', err);
    return;
  }
  console.log('播放速度:', el.playbackRate); // 2.0
});