user25466: I am trying to render a video spectrum of music using showwaves ... I need it to render with a transparent background (i think this is called an alpha channel?)... 
I tried yuva420p but it's still rendering a black background... here's what I'm doing:
ffmpeg -i music.mp3 -filter_complex \
"[0:a]showwaves=s=1920x1080:mode=line:colors=white:draw=full,format=yuva420p[v]" \
-map "[v]" -map 0:a output.mp4;

Can anyone help? I know I'm close...

user1871: The default codec for MP4 is x264 which does not support alpha channel. Use PNG.
ffmpeg -i music.mp3 -filter_complex \
"[0:a]showwaves=s=1920x1080:mode=line:colors=white:draw=full,format=rgbap[v]" \
-map "[v]" -map 0:a -c:v png output.mp4;


25466: <p>I am trying to render a video spectrum of music using <code>showwaves</code> ... I need it to render with a <em>transparent</em> background (i think this is called an alpha channel?)... </p>

<p>I tried <code>yuva420p</code> but it's still rendering a black background... here's what I'm doing:</p>

<pre><code>ffmpeg -i music.mp3 -filter_complex \
"[0:a]showwaves=s=1920x1080:mode=line:colors=white:draw=full,format=yuva420p[v]" \
-map "[v]" -map 0:a output.mp4;
</code></pre>

<p>Can anyone help? I know I'm close...</p>
 1871: <p>The default codec for MP4 is x264 which does not support alpha channel. Use PNG.</p>

<pre><code>ffmpeg -i music.mp3 -filter_complex \
"[0:a]showwaves=s=1920x1080:mode=line:colors=white:draw=full,format=rgbap[v]" \
-map "[v]" -map 0:a -c:v png output.mp4;
</code></pre>
