libav / ffmpeg output optimisation for small file sizes
<p>I am using the following command to take an audio mp3 file and make a video out of it (by using a static jpg picture). My aim is to get a mp3 audio that is as small as possible with still acceptable quality.</p>

<pre><code>frequency="11000"
bitrate="45000"
avconv -loop 1 -i a.jpg -i audio.mp3 -shortest -r 1 -metadata STEREO_MODE=mono -c:v libx264 -ar "$frequency" -b:a "$bitrate" -ac 0 result.mkv
</code></pre>

<p>My questions are:
1. how can I achieve that the resulting file is MONO?
2. is it possible to reduce the bitrate furthermore? I would like to use values below 45000, too.
3. My aim is to get control of the parameters that influence the file size most significantly. Presently I know that the frequency is quite important. Are there any other parameters that would help me to get a very small output file with still acceptable quality?</p>

<p>Thanks in advance.</p>