user6171: I have a comp that I made that is a write-on effect.  I have selected the alpha channel toggle so in my view, I see the checkered background. 
When I queue to render, I select lossless + alpha (I've also tried custom RGB + alpha) with quicktime selected and it renders a white background instead of transparent one. I had selected the white background, but transparency was toggled when I did the export, and so was the lossless + alpha. 
Please help. 

user3295: Did you try re-importing the rendered video into After Effects? You should definitely have transperency with these settings.
If you only tried to play this back as a webm video in chrome and safari you won't see transparency, neither browser is supporting webm with transparency right now. Only Googles Cannary project offers this future at the moment.
As Joonas mentioned in the comments, the jquery-seeThru project is offering a workaround for that.

user2836: There actually is no such thing as a "transparent" background in video.  Instead what you have is either 3 channel video (red, green and blue value for each pixel) or 4 channel (red, green, blue and alpha values for each pixel).  
The Alpha channel provides details about how opaque each pixel should be, however unless the video player playing the video file supports reading this extra channel of data, it won't actually do anything special.  
Generally, unless the background image will actually be different for different users, your best bet may be to actually import the portion of the graphic that will be behind the video and actually record the video with the background behind it.  Then, when you position things together correctly, it will appear relatively seamless (though you have to be careful about the color encoding to make sure colors match.)  There is also some possibility that people's players will apply a color profile anyway and thus make the video frame have a slight color alteration from the normal background.
Otherwise, the jquery-seeThru project that Professor Sparkle mentioned is probably the best bet.

user10726: To get a transparent Quicktime Video:

select the composition
press Ctrl+M to add it to the render queue, 
click on Output Module to choose the File Format, 
select Quicktime Container Format for Video Output,
select RGB+A to render RGB and Alpha channel


6171: <p>I have a comp that I made that is a write-on effect.  I have selected the alpha channel toggle so in my view, I see the checkered background. </p>

<p>When I queue to render, I select <em>lossless + alpha (I've also tried custom RGB + alpha)</em> with <strong>quicktime</strong> selected and it renders a <strong>white background instead of transparent one</strong>. I had selected the white background, but transparency was toggled when I did the export, and so was the lossless + alpha. </p>

<p>Please help. </p>
 3295: <p>Did you try re-importing the rendered video into After Effects? You should definitely have transperency with these settings.</p>

<p>If you only tried to play this back as a webm video in chrome and safari you won't see transparency, neither browser is supporting webm with transparency right now. Only Googles Cannary project offers this future at the moment.</p>

<p>As Joonas mentioned in the comments, the <a href="https://github.com/m90/jquery-seeThru" rel="nofollow">jquery-seeThru</a> project is offering a workaround for that.</p>
 2836: <p>There actually is no such thing as a "transparent" background in video.  Instead what you have is either 3 channel video (red, green and blue value for each pixel) or 4 channel (red, green, blue and alpha values for each pixel).  </p>

<p>The Alpha channel provides details about how opaque each pixel should be, however unless the video player playing the video file supports reading this extra channel of data, it won't actually do anything special.  </p>

<p>Generally, unless the background image will actually be different for different users, your best bet may be to actually import the portion of the graphic that will be behind the video and actually record the video with the background behind it.  Then, when you position things together correctly, it will appear relatively seamless (though you have to be careful about the color encoding to make sure colors match.)  There is also some possibility that people's players will apply a color profile anyway and thus make the video frame have a slight color alteration from the normal background.</p>

<p>Otherwise, the jquery-seeThru project that Professor Sparkle mentioned is probably the best bet.</p>
 10726: <p>To get a transparent Quicktime Video:</p>

<ul>
<li>select the composition</li>
<li>press <kbd>Ctrl</kbd>+<kbd>M</kbd> to add it to the render queue, </li>
<li>click on <em>Output Module</em> to choose the <em>File Format</em>, </li>
<li>select <em>Quicktime Container Format</em> for Video Output,</li>
<li>select <em>RGB+A</em> to render RGB and Alpha channel</li>
</ul>
