MP4 vs DivX: Filesize and Playback Question

[hk]

Hi,
comparing an original avi file coded with DivX5.02pro and the mp4 moviefile, created with mpegcreator60 from the original,
the divX file is slightly bigger. However, mpegcreator60 is said to just rewrite the flags. How come?

Does mpegcreator60 supports b-frames, Qpel and GMC?

Why is playback of the mp4file (on WMP6.4 with envivioTVplugIN)
much choppier than the original divX avi file?

Any ideas?
HK

[tanksimpson]

Envivio plug-in doesn't play back Divx 5.02 Pro b-frames, that's why it seems choppy. It DOES however, play back b-frames just fine from the new Xvid builds, so you might want to give Xvid a try. Qpel from either Xvid or Divx does not play back properly in Envivio - you get weird colors. GMC seems to work okay, but I am not an expert on what GMC is supposed to do or look like, so I can't really say for sure. I am pretty sure that mpeg4ip tools are not responsible for any of these problems. BTW, it is normal for the .mp4 to be smaller than the original .avi, unless you have "hinted" the tracks and "optimized" the file, both of which add size to the .mp4 - only necessary for streaming.

[hk]

Thanksimpson for your response! It´s what I thought it may be, that envivio does not play back bframes. However, envivio support has said, that the plugIn v.1.2 supports bframes...strange.
Anyway, how come that bframes coded with Divx and those coded with Xvid are different? Bfames are not just bframes?

HK

[tanksimpson]

Apparently so. I'm sure if you ask one of the "experts" in the Xvid forum, they will be happy to give you the technical explanation for why Divx b-frames suck compared to Xvid's :) ...unless of course they just tell you to "use the search button" :D I do not know the details, but I gather that Divx's b-frames are not truly MPEG-4 compliant. You might also want to ask Boris on the support forum at envivio.com.

[DeXT]

Keep in mind that EnvivioTV uses its own MPEG-4 decoder instead of DivX (no matter the source of the MPEG-4 stream), which may be less optimized than DivX decoder, hence the choppy playback. You can verify this by looking at the filters being used while in playback.