user1090: The ffmpeg manual states that:

libvpx-vp9 is the VP9 video encoder for ​WebM, an open, royalty-free media file format.

What is the difference between the VP9 and WebM?

user1760: VP9 is a video format. Another example is H.264.
WebM is a container format that VP9 goes into. It is equivalent to the MP4 container format for the H.264 video format.
libvpx is a video encoder (or codec) which outputs the VP8 or VP9 video formats. Another encoder example is x264 which outputs the H.264 video format.

1090: <p>The <a href="https://trac.ffmpeg.org/wiki/Encode/VP9" rel="nofollow noreferrer">ffmpeg manual</a> states that:</p>

<blockquote>
  <p>libvpx-vp9 is the VP9 video encoder for ​WebM, an open, royalty-free media file format.</p>
</blockquote>

<p>What is the difference between the VP9 and WebM?</p>
 1760: <p>VP9 is a <strong>video format</strong>. Another example is H.264.</p>

<p>WebM is a <strong>container format</strong> that VP9 goes into. It is equivalent to the MP4 container format for the H.264 video format.</p>

<p>libvpx is a <strong>video encoder</strong> (or <strong>codec</strong>) which outputs the VP8 or VP9 video formats. Another encoder example is x264 which outputs the H.264 video format.</p>
