file 'path/to/seg1.mp4'
file 'path/to/seg2.mp4'
file 'path/to/seg3.mp4'

ffmpeg -f concat -safe 0 -i list.txt -c copy output.mp4

package com.donglin.skyzlm.event;

import java.io.BufferedWriter;
import java.io.File;
import java.io.FileWriter;
import java.io.IOException;
import java.util.List;

public class MergeVideos {

    // ffmpeg 可執(zhí)行命令（系統(tǒng) PATH 中必須能執(zhí)行 ffmpeg）
    private static final String FFMPEG = "ffmpeg";

    public static void main(String[] args) {
        // 1）分片視頻列表
        List<String> clips = List.of(
                "seg1.mp4",
                "seg2.mp4",
                "seg3.mp4"
        );

        // 2）生成合并列表文件
        String listFilePath = "videos/list.txt";
        try {
            createConcatListFile(clips, listFilePath);
        } catch (IOException e) {
            System.err.println("生成 list.txt 失敗: " + e.getMessage());
            return;
        }

        // 3）合并輸出
        String output = "videos/merged.mp4";
        boolean success = mergeWithFFmpeg(listFilePath, output);

        System.out.println("合并 " + (success ? "成功" : "失敗") + ", 輸出：" + output);
    }

    /**
     * 生成 concat 的 list.txt
     */
    private static void createConcatListFile(List<String> clips, String listFilePath) throws IOException {
        File file = new File(listFilePath);
        try (BufferedWriter writer = new BufferedWriter(new FileWriter(file))) {
            for (String clip : clips) {
                // FFmpeg concat list.txt 格式：file '路徑'
                writer.write("file '" + clip.replace("\\", "/") + "'");
                writer.newLine();
            }
        }
        System.out.println("生成 list.txt: " + file.getAbsolutePath());
    }

    /**
     * 調(diào)用 FFmpeg concat 合并
     */
    private static boolean mergeWithFFmpeg(String listFilePath, String outputPath) {
        try {
            ProcessBuilder pb = new ProcessBuilder(
                    FFMPEG,
                    "-f", "concat",
                    "-safe", "0",
                    "-i", listFilePath,
                    "-fflags", "+genpts",
                    "-c:v", "libx264",     // 可根據(jù)需要調(diào)整 codec
                    "-preset", "veryfast",
                    "-crf", "20",
                    "-c:a", "aac",
                    "-b:a", "128k",
                    "-movflags", "+faststart",
                    outputPath
            );

            // 合并 stdout 和 stderr 輸出
            pb.redirectErrorStream(true);

            Process process = pb.start();
            // 打印 FFmpeg 輸出（可選）
            new Thread(() -> {
                try (var is = process.getInputStream()) {
                    is.transferTo(System.out);
                } catch (IOException ignored) {}
            }).start();

            int exit = process.waitFor();
            return exit == 0;

        } catch (IOException | InterruptedException e) {
            e.printStackTrace();
            return false;
        }
    }
}

writer.write("file '" + clip.replace("\\", "/") + "'");

file 'seg1.mp4'
file 'seg2.mp4'
file 'seg3.mp4'

ffmpeg -f concat -safe 0 -i list.txt -c:v libx264 -c:a aac ...