user3643: I'm doing some rendering in Vegas Pro and notice that if I select MainConcept (which gives me an HTML5 compatible MP4) the audio tab only has options for the bit rate and the sample rate. Before rendering, I combined both left and right channels on the timeline, but once rendered, the video file has two audio channels.
This is normally not a problem, but in this case, the audio is only voice and I'm concerned about file size, so if I could render with a mono channel, I would be able to get a higher bit rate for audio quality, but keep the file size small.
What Vegas is doing is taking the single channel audio from the timeline, duplicating it, setting a left and right channel, then cuts the set bitrate in half for each channel. So if I want 96kbps mono, I actually end up with  stereo, 48kbps on each channel.
Is this an inherent issue with MainConcept file types? I notice that with others I can actually select mono in the audio tab, but not with MainConcept. I thought I read a short half sentence saying as much on some forum, but not sure.
If there is a way to have an HTML5 compatible MP4 with mono audio, please tell me how.

user1871: The Mainconcept or Sony codecs in Vegas are subpar for low-bitrate output such as needed for HTML5 use. Use ffmpeg to generate your HTML5 videos. Yes, mono audio is acceptable for HTML5 use, but once you use ffmpeg/x264 for generating those videos, the 6kB/s savings you get from switching to mono audio won't matter much if at all.
Get the 32-bit static build of ffmpeg from here. Render a high bitrate Mainconcept MP4 from Vegas, say, 12 Mbps. And then run the following ffmpeg command:
ffmpeg -i "vegas-output.mp4" -crf 23 -c:a aac -b:a 96k -strict -2 -movflags +faststart "html5-video.mp4"

If you still want mono audio, insert
-ac 1

after aac.
If you don't like the quality or size is too large, then play around with the CRF value. They go from 0 to 63 with lower being better. 18 to 28 is the usual range you want to stick with. 

3643: <p>I'm doing some rendering in Vegas Pro and notice that if I select MainConcept (which gives me an HTML5 compatible MP4) the audio tab only has options for the bit rate and the sample rate. Before rendering, I combined both left and right channels on the timeline, but once rendered, the video file has two audio channels.</p>

<p>This is normally not a problem, but in this case, the audio is only voice and I'm concerned about file size, so if I could render with a mono channel, I would be able to get a higher bit rate for audio quality, but keep the file size small.</p>

<p>What Vegas is doing is taking the single channel audio from the timeline, duplicating it, setting a left and right channel, then cuts the set bitrate in half for each channel. So if I want 96kbps mono, I actually end up with  stereo, 48kbps on each channel.</p>

<p>Is this an inherent issue with MainConcept file types? I notice that with others I can actually select mono in the audio tab, but not with MainConcept. I thought I read a short half sentence saying as much on some forum, but not sure.</p>

<p>If there is a way to have an HTML5 compatible MP4 with mono audio, please tell me how.</p>
 1871: <p>The Mainconcept or Sony codecs in Vegas are subpar for low-bitrate output such as needed for HTML5 use. Use ffmpeg to generate your HTML5 videos. Yes, mono audio is acceptable for HTML5 use, but once you use ffmpeg/x264 for generating those videos, the 6kB/s savings you get from switching to mono audio won't matter much if at all.</p>

<p>Get the 32-bit static build of ffmpeg from <a href="http://ffmpeg.zeranoe.com/builds/" rel="nofollow noreferrer">here</a>. Render a high bitrate Mainconcept MP4 from Vegas, say, 12 Mbps. And then run the following ffmpeg command:</p>

<pre><code>ffmpeg -i "vegas-output.mp4" -crf 23 -c:a aac -b:a 96k -strict -2 -movflags +faststart "html5-video.mp4"
</code></pre>

<p>If you still want mono audio, insert</p>

<pre><code>-ac 1
</code></pre>

<p>after aac.</p>

<p>If you don't like the quality or size is too large, then play around with the CRF value. They go from 0 to 63 with lower being better. 18 to 28 is the usual range you want to stick with. </p>
