如何使用FFMPEG转码文件并在Java servlet的响应中流式传输输出文件？

Question

基本上,这就是我要做的事情:1.用户将URL作为GET参数传递给我的servlet.2. Servlet使用ProcessBuilder将该URL中包含的媒体转换为有效的媒体格式(即:MP3).3. servlet将由FFMPEG转码的输出文件流回到浏览器.

1和2工作正常,但它是3我有问题.我能做的最好的事情是为正在转码的输出文件创建一个FileInputStream,并将其作为响应发送,但它不起作用.我的猜测是,因为我正在尝试流式传输文件.

无论如何拦截FFMPEG中的输出文件参数并将其读入InputStream？在我看来,似乎不应该难以获取输入文件A,将其转码为输出文件B,然后将输出文件B流式传输回客户端.

ProcessBuilder pb = new ProcessBuilder("ffmpeg.exe", "-i", url, "file.mp3");
    Process p = pb.start();

    final InputStream inStream = p.getErrorStream();

    new Thread(new Runnable() {

    public void run() {
            InputStreamReader reader = new InputStreamReader(inStream);
            Scanner scan = new Scanner(reader);
            while (scan.hasNextLine()) {
                System.out.println(scan.nextLine());
            }
        }
    }).start();

    ServletOutputStream stream = null;
    BufferedInputStream buf = null;
    try {

        stream = response.getOutputStream();
        File mp3 = new File(file.mp3");

        //set response headers
        response.setContentType("audio/mpeg");

        response.addHeader("Content-Disposition", "attachment; filename=file.mp3");

        response.setContentLength(-1);

        //response.setContentLength((int) mp3.length());

        FileInputStream input = new FileInputStream(mp3);
        buf = new BufferedInputStream(input);
        int readBytes = 0;
        //read from the file; write to the ServletOutputStream
        while ((readBytes = buf.read()) != -1) {
            stream.write(readBytes);
        }
    } catch (IOException ioe) {
        throw new ServletException(ioe.getMessage());
    } finally {
        if (stream != null) {
            stream.close();
        }
        if (buf != null) {
            buf.close();
        }
    }

Answer 1

FFmpeg不必写入文件.它可以写入stdout:

ffmpeg -i $input -f mp3 -

-意味着标准输出.由于没有文件名,您需要指定格式-f.

如果你像这样调用它,你可以直接从Process's 读取mp3流InputStream.