A20 cpu audio encoding

We want to check what cpu audio encoding looks like on the A20.

This is the audio output we got from the BMD devices. We might want to err close to that:

Input #0, mpegts, from 'cam-trim.ts':
Duration: 01:06:00.05, start: 1.410667, bitrate: 2489 kb/s
Program 1 
Metadata:
service_name    : Service01
service_provider: FFmpeg
Stream #0:0[0x100]: Video: h264 (High) ([27][0][0][0] / 0x001B), yuv420p(progressive), 1280x720 [SAR 1:1 DAR 16:9], 50 fps, 50 tbr, 90k tbn, 100 tbc
Stream #0:1[0x101]: Audio: aac (LC) ([15][0][0][0] / 0x000F), 48000 Hz, stereo, fltp, 253 kb/s

Example from http://www.music.helsinki.fi/tmt/opetus/uusmedia/esim/index-e.html : http://www.music.helsinki.fi/tmt/opetus/uusmedia/esim/a2002011001-e02.wav (44.1 KHz, 14 bit stereo wav in).

This takes ~25-28% of one A9 core on an Allwinner A20 based bpi M1 to encode to 256Kb/s 16 bit stereo 48 KHz aac when running at live encoding speed. Including i/o of course, so should be lower on a final...

ffmpeg -re -i a2002011001-e02.wav -b:a 256k -ar 44100 test3.aac