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In my application, I fetch multiple audio (mp3) files from a server and get them as input stream or byte array. I convert them to a list of AudioInputStreams then and at the moment concat the data to one large ByteArrayInputStream. I then convert that to an AudioInputStream again and provide the data in it (byte[]) through a REST endpoint. My frontend is a react application where users can listen to it and download it.

Unfortunately, this process seems to break the mp3 header and the length is wrong. My frontend player does play the file to the end, so generally, the process is even working, but if I download it as a file the length is always the same as from the first file I concatenated in backend and some audio players won't even play to the end.

The question is: how to concat two mp3 byte-arrays properly in java?

Alexander Ivanchenko
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mysterix
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    Mby this helps? https://stackoverflow.com/questions/46643266/how-to-merge-two-mp3-files-in-java – Tayfun Omer Jul 28 '22 at 12:16
  • this is exactly what i want to do, but it doesn't work with mp3. For mp3 files the frameLength is not a valid concept, so it gives -1. It will work even with giving a dummy length or the byte length or something, but no matter where i write it to file the duration is wrong which is not really acceptable. Some player will even play it but most will stop way too early because of the wrong metadata. – mysterix Jul 28 '22 at 12:53
  • Please provide enough code so others can better understand or reproduce the problem. – Community Jul 28 '22 at 17:01

1 Answers1

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ok, I managed to solve the task with Jaffree which is very similar to ffmpeg-cli-wrapper which is a java wrapper for ffmpeg. This may not have the greatest performance because an external program is started but if fits my needs here. The relevant code is:

try (ByteArrayOutputStream byteArrayOutputStream = new ByteArrayOutputStream()) {
    for (InputStream inputStream : inputStreams) {
        FFmpeg.atPath()
            .addInput(PipeInput.pumpFrom(inputStream))
            .addOutput(
                PipeOutput.pumpTo(byteArrayOutputStream)
                    .setFormat("mp3")
            )
                .execute();
    }
}

where inputStreams are valid mp3 data InputStreams

mysterix
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