H.263, MPEG-4 ASP and 3GP container

[numaios]

Hello!

I always thought MPEG-4 ASP was the same as H.263 (since the default quantization matrix in XviD and DivX codecs is H.263). But now I've been trying mobile formats/containers and I've seen that in 3GP container you can store MPEG-4 ASP, H.263 or H.264/MPEG-4 AVC (while MP4 can only store ASP and AVC).

So I deduce MPEG-4 ASP is not the same as H.263.

I did some search trying to find information about H.263 and I only found that H.263 is a video codec from 1998, but anything else. In this subforum (New and alternative video codecs) I haven't found anything. So what is exactly H.263? Is a video codec compliant with MPEG-4 ASP profile? Or is it something different?

Thanks in advance.

[Manao]

H263 is almost equivalent to mpeg4 simple profile ( hence, no bframes, no qpel, no gmc, no interlacing, no custom quantization ). The differences are subtil :

- the bitstream is written in the "short header" mode, which mostly make the bitstream a lot simpler.
- the motion vectors can't reference pixels outside the reference frame.
- the intra prediction is disabled ( no DC prediction, nor AC )
- the resolution can only be 176x144, 352x288, 720x576 and two other I don't remember.
- the framerate is limited too.
- escape codes for quantized DCT coefficients are simpler.
- no 4mv mode
- and surely a lot of other minor differences.

The big losses, efficiency-wise are in order the 4mv, the escape codes, the limitation or motion vectors and the intra prediction. It amounts roughly to 0.4 / 0.5 dB ( or a 10 % bitrate loss ).

A decoder that handle mpeg4 must decode h263.

[foxyshadis]

h.263 also uses an inloop block filter, like the rest of the h.26* specs. mpeg4-asp decoders would just ignore that and subtly corrupt the output, but I think its inloop is mostly only used in the real-time teleconferencing tools anyway.

[Manao]

Inloop is only used in h263+ ( which, in addition to in loop, enables overlapped motion compensation ).

Roughly, mpeg & h26x are interleaved :
mpeg1 ~ h261 < mpeg2 ~ h262 < h263 ~< mpeg4p2 < h263+ < h263++ < h264 ~ mpeg4p10 ~ avc.

[numaios]

Thank you very much for your answers! :)

So if I can choose between H.263 and MPEG-4 SP, the last one would be better.

This is amazing: h263+ is better than MPEG-4 SP? I would never have guessed...

Is there any freeware H.263/H.263+/H.263++ encoder? In fact the only H.263 encoder I know is Apple QuickTime...

[Inventive Software]

Try ffdshow, if you can find a working build. There are reports that H.263 encoding is broken in latest ffdshow_tryouts builds.

[numaios]

:thanks:
Another question: any container incompatibility between H.263+/H.263++ <-->*.3gp/*.3g2?