ProcessBuilder in Java on Raspberry Pi 3 not showing error/input stream for omxplayer

Question

I am doing a little program in Java on a Raspberry pi 3 Jessie, and I am trying to use omxplayer to play a sound from inside the java program.

I have the following code:

ProcessBuilder p = new ProcessBuilder("omxplayer", "/path/to/wav");
p.redirectErrorStream(true);

Process pr = p.start();
BufferedReader bufferedReader = new BufferedReader(new InputStreamReader(pr.getInputStream()));
Executors.newSingleThreadExecutor().execute(new Runnable() {
    @Override
    public void run() {
        try {
            String line = "";
            while((line = bufferedReader.readLine()) != null) {
                System.out.println("Reading " + line);
            }
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
});

The program will play the sound correctly, but will not output anything until it reaches the end of the wav and then prints all. However, when I launch the same command directly in a terminal, I can see text showing during the wav.

For example, when I press "+" or "-" in a terminal with omxplayer running, it changes the volume and prints "Current volume : blabla mB", but when I send through the ProcessBuilder "+" or "-", I can hear the sound of my wav changes, but still no outputs.

It is weird because I have used ProcessBuilder for many other uses, and have never encountered a problem as such.

Do you think the problem is with omxplayer's implementation? Or am I doing something wrong here?

EDIT:

I have tried reading the stream without the BufferedReader as such:

InputStream inputStream = pr.getInputStream();
Executors.newSingleThreadExecutor().execute(new Runnable() {
    @Override
    public void run() {
        try {
            int read;
            while((read = inputStream.read()) >= 0) {
                System.out.println("Reading " + (char)read);
            }
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
});

in case the omxplayer did not send any line returns, but the problem remains.

Answer 1

I had exactly the same problem and could fix it with the parameter -s (statistics). In this case, the player continuously puts status information and also all the start infos.