user21249: To my understanding, there is the container format (MP4, MOV, 3GP, AVI) and the codecs (Theora, VP8, H264, XVid, DivX).
For what I understand, the container format and the codecs are independent and it seems that it would theoretically be possible to have a MP4 which contains some video encoded with DivX. 
Would it work? I mean, would standard video players be able to play it?
Also, I don't understand why H.264 (a codec) is defined in the MPEG-4 (a container) specification.
As H.265/HVEC is to replace H.264, will there be a new container format? Or will there be some MP4 files containing some videos encoded in H.265?

user1871: MPEG-4 is not a container specification. It's a suite of specifications. Parts 12 and 14 define containers (MP4). Part 2 defines a video codec, whose encoder implementations are DivX and Xvid. Part 10 defines another video codec AVC a.k.a. H.264.
You can get a list of codecs, which can theoretically be present in a MP4 at http://mp4ra.org/codecs.html
Whether a given muxer/software offers the feature to include a codec in MP4, or whether a given player accepts a codec in a MP4, depends on the software developer. Generally, MPEG-4 Part 2 should be accepted but players can be finicky about the codec tag and may only play the video if they recognize the tag.
HEVC can be muxed in a MP4 and there's no dedicated or new container for it.

21249: <p>To my understanding, there is the container format (MP4, MOV, 3GP, AVI) and the codecs (Theora, VP8, H264, XVid, DivX).</p>

<p>For what I understand, the container format and the codecs are independent and it seems that it would theoretically be possible to have a MP4 which contains some video encoded with DivX. </p>

<p><strong>Would it work?</strong> I mean, would standard video players be able to play it?</p>

<p>Also, I don't understand why H.264 (a codec) is defined in the MPEG-4 (a container) specification.</p>

<p>As H.265/HVEC is to replace H.264, will there be a new container format? Or will there be some MP4 files containing some videos encoded in H.265?</p>
 1871: <p>MPEG-4 is not a container specification. It's a suite of specifications. Parts 12 and 14 define containers (MP4). Part 2 defines a video codec, whose encoder implementations are DivX and Xvid. Part 10 defines another video codec AVC a.k.a. H.264.</p>

<p>You can get a list of codecs, which can theoretically be present in a MP4 at <a href="http://mp4ra.org/codecs.html" rel="noreferrer">http://mp4ra.org/codecs.html</a></p>

<p>Whether a given muxer/software offers the feature to include a codec in MP4, or whether a given player accepts a codec in a MP4, depends on the software developer. Generally, MPEG-4 Part 2 should be accepted but players can be finicky about the codec tag and may only play the video if they recognize the tag.</p>

<p>HEVC can be muxed in a MP4 and there's no dedicated or new container for it.</p>
