ffmpeg.exe (encode PCM to AAC-LC and pack the data to adts format)

exec ffmpeg.exe from my program
ffmpeg.exe -f f32le -ar 48000 -ac 2 -i - -f u16le -ar 24000 -ac 1 -map 0 -codec:a aac -profile aac_low -ab 8k -f adts -
my program passes captured PC internal sound data through stdin of ffmpeg.exe process
IMPORTANT: passing samples is needed 1024 samples at the same time (= pass 1024 samples with one write call and then call flush)
stdout of ffmpeg.exe is read by my program and send it to Android app.
- IMPORTANT: you should read ffmpeg write data with one read call (it should be a adts frame)

Decoder with MediaCodec class

decode.cs

            HandlerThread callbackThread = new HandlerThread("AACDecodingHandler");
            callbackThread.Start();
            Handler handler = new Handler(callbackThread.Looper);

            decoder = MediaCodec.CreateDecoderByType("audio/mp4a-latm");
            // samplingRate and ch is your required value
            var format = MediaFormat.CreateAudioFormat("audio/mp4a-latm", samplingRate, ch);

            // IMPORTANT: csd_data is byte array (7 elements). this data is exist head of stream (= stdout of ffmpeg.exe)
            //            this 7 bytes is adts fixed header of first frame but you should not removed it from frame.
            //            you should pass first adts frame to InputBuffer with header (first 7 bytes).
            int profile = (csd_data[2] & 0xC0) >> 6;
            int srate = (csd_data[2] & 0x3C) >> 2;
            int channel = ((csd_data[2] & 0x01) << 2) | ((csd_data[3] & 0xC0) >> 6);
            byte csd0_0 = (byte)(((profile + 1) << 3) | srate >> 1);
            byte csd0_1 = (byte)(((srate << 7) & 0x80) | channel << 3 );
            byte[] bytes = new byte[] { csd0_0, csd0_1 };
            ByteBuffer csd = ByteBuffer.Wrap(bytes);
            format.SetInteger(MediaFormat.KeyIsAdts, 1);

            format.SetByteBuffer("csd-0", csd);

            // cbk is your callback class
            decoder.SetCallback(cbk, handler);
            decoder.Configure(format, null, null, 0);

            decoder.Start();

Useful tool for validating your AAC adts data

https://gist.github.com/yohhoy/8ccd6d89e18818662bd4/#file-aac_parser-py

Whole code

Enjoy!