降低mp3文件的比特率

Question

使用下面的方法，我可以降低mp3的比特率（使用xuggler lib），

public void reduce_file(File input, final File output, final int kbps, int index) { //modify on your convenience
        // create a media reader

        try {

            IMediaReader mediaReader = ToolFactory.makeReader(input.getPath());
            System.out.println("around");
            // create a media writer
            IMediaWriter mediaWriter = ToolFactory.makeWriter(output.getPath(), mediaReader);

            // add a writer to the reader, to create the output file
            mediaReader.addListener(mediaWriter);

            // add a IMediaListner to the writer to change bit rate
            mediaWriter.addListener(new IMediaListener() {
                @Override
                public void onVideoPicture(IVideoPictureEvent ivpe) {
                }

                @Override
                public void onAudioSamples(IAudioSamplesEvent iase) {
                }

                @Override
                public void onOpen(IOpenEvent ioe) {
                    System.out.println("open");
                }

                @Override
                public void onClose(ICloseEvent ice) {
                    System.out.println("closed");
                }

                @Override
                public void onAddStream(IAddStreamEvent event) {
                    IStreamCoder streamCoder = event.getSource().getContainer().getStream(event.getStreamIndex()).getStreamCoder();
                    //streamCoder.setFlag(IStreamCoder.Flags.FLAG_QSCALE, false);
                    streamCoder.setBitRate(kbps);
                    streamCoder.setBitRateTolerance(0);
                    //streamCoder.setSampleRate(22050);
                    streamCoder.setSampleFormat(IAudioSamples.Format.FMT_S32);
                    // streamCoder.setChannels(2);
                }

                @Override
                public void onOpenCoder(IOpenCoderEvent ioce) {
                }

                @Override
                public void onCloseCoder(ICloseCoderEvent icce) {
                }

                @Override
                public void onReadPacket(IReadPacketEvent irpe) {
                }

                @Override
                public void onWritePacket(IWritePacketEvent iwpe) {
                }

                @Override
                public void onWriteHeader(IWriteHeaderEvent iwhe) {
                    iwhe.getSource().getContainer().writeHeader();
                }

                @Override
                public void onFlush(IFlushEvent ife) {
                }

                @Override
                public void onWriteTrailer(IWriteTrailerEvent iwte) {
                }
            });

            while (mediaReader.readPacket() == null) ;

        } catch (Exception ex) {
        }
    }
}

但是，对于某些媒体文件，我收到此错误：

ERROR org.ffmpeg - [mp3 @ 0x4e6e8e0] Header missing.

如何更正此错误，或者是否有其他lib。这将使我实现这一目标。提前谢谢。