java - 当指定 -vcodec 副本时，FFmpeg 挂起(通过 ProcessBuilder 从 Java 调用)

Question

我正在尝试使用 ffmpeg 将字节数组导出到视频文件，但与我一起工作的人坚持要求我在其参数中使用 -vcodec copy 。然而，这会导致代码挂起，而如果我不使用 -vcodec copy，代码将不会挂起。我不知道问题出在哪里，过去两个小时我一直在尝试调试这段代码。

这是相关的代码部分。我在代码挂起的行的上方和下方添加了注释。有人可以帮助我吗？

        // This is the tricky part. We need to build an ffmpeg process that
        // takes input from stdin, and then plug Java into that.
        ProcessBuilder ffmpegBuilder = new ProcessBuilder();
        String[] cmd = {"ffmpeg", "-i", "-","-vcodec", "copy", directory
                + "/" + fileName};
        StringBuilder combinedCmd = new StringBuilder();
        for (String s : cmd) {
            combinedCmd.append(s);
            combinedCmd.append(" ");
        }
        mLogger.log(Level.INFO,"Final command is " + combinedCmd.toString());
        ffmpegBuilder.command(cmd);
        ffmpegBuilder.redirectErrorStream(true); // So that stdout and stderr go
                                                    // to the same stream.
        byte[] dataToWrite = new byte[data.size()];
        for (int i = 0; i < dataToWrite.length; i++) {
            dataToWrite[i] = data.get(i); // Is there really STILL no better way
                                            // to convert an ArrayList to an
                                            // array?!
        }
        try {
            Process ffmpeg = ffmpegBuilder.start();
            OutputStream stdin = ffmpeg.getOutputStream();
            BufferedReader stdout = new BufferedReader(new InputStreamReader(
                    ffmpeg.getInputStream()));
//HANGS AT THIS LINE vvvvvvvvvvvvvvvv
            stdin.write(dataToWrite);
//HANGS AT THIS LINE ^^^^^^^^^^^^^^^^

            String line = "I know a song that gets on everybody's nerves...";
            while ((line != null) && stdout.ready()) {
                line = stdout.readLine();
                mLogger.log(Level.INFO, line);
            }
            try {
                ffmpeg.waitFor(2, TimeUnit.SECONDS);
                ffmpeg.destroyForcibly();
            } catch (InterruptedException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
        } catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }

Answer 1

结果发现程序在写入数据的过程中挂起了。那里有大量的数据，我知道此时出了点问题，所以我试图告诉 java 进程开始从我制作的 BufferedReader 中读取 stdout。这解决了问题。事实证明，BufferedReader 已满，并且由于 stdout 无处可去，整个进程挂起。我在这里更改了挂接到此代码的行:

for (int i = 0;i < dataToWrite.length;i++) {
    stdin.write(dataToWrite[i]);
    if (stdout.ready()) {
        String line = stdout.readLine();
        mLogger.log(Level.INFO, line);
    }
}

这解决了一切。