FFmpegFrameGrabber crashes 100% of time attempting

Question

I am attempting to use javacv/ffmpeg to compress video on an Android device prior to upload. I am using this code:

FrameGrabber grabber = new FFmpegFrameGrabber(inputFile.getAbsolutePath()); 
grabber.start();
FFmpegFrameRecorder recorder = new FFmpegFrameRecorder(outputFile.getAbsolutePath(), 
   grabber.getImageWidth(), grabber.getImageHeight(), 
   grabber.getAudioChannels()); 

recorder.setVideoCodec(com.googlecode.javacv.cpp.avcodec.AV_CODEC_ID_MPEG4);
recorder.setAudioCodec(com.googlecode.javacv.cpp.avcodec.AV_CODEC_ID_PCM_S16LE);
recorder.setPixelFormat(com.googlecode.javacv.cpp.avutil.AV_PIX_FMT_YUV420P);

/* Unclear if I need these lines or not */
// recorder.setFrameRate(grabber.getFrameRate()); 
// recorder.setSampleRate(grabber.getSampleRate()); 
// recorder.setFormat("mp4");
/* End unclear lines */

recorder.start();

Frame frame; 
int totalFrames = grabber.getLengthInFrames();
for (int i = 0; i < totalFrames; i++) {
  frame = grabber.grabFrame();
  if (frame == null) break;
  recorder.record(frame);
}

recorder.stop();
grabber.stop();

This code crashes 100% of the time at FFmpegFrameGrabber line 584, which is the line:

frame.samples = samples_buf.position(0).limit(data_size / av_get_bytes_per_sample(samples_frame.format()));

This is because samples_buf is null, because samples_frame.format() does not appear to match any of the cases (AV_SAMPLE_FMT_U8, AV_SAMPLE_FMT_S16, AV_SAMPLE_FMT_S32, AV_SAMPLE_FMT_FLT, AV_SAMPLE_FMT_DBL).

I attempted to avoid this crash by using the grab() method instead of the grabFrame() method, because the grab() method skips audio processing. However, the video I end up with does not play back when I extract it off the device and attempt playback in a web browser, for example.

I have tried numerous iterations of this code, including this code, all to no avail, all crashing because of line above.

Can anyone advise the shortest working path to compressing a video using javacv/ffmpeg on Android?

Thanks!