ffmpegX and fast mpeg1

[Pix]

THE question is right at the bottom (for those who don't want to read all my story)

I'm using ffmpegX for VCD/SVCD encoding.
When it comes to VCD, I normally used the appropriate preset (VCD PAL) and the result depends very much on the source (I have the best like the worse).

However, in the past, there was an option which used ffmpeg engine instead of mpeg2enc. It still exists, as far as I know, it's called fast mpeg1.

Advantages :
-It works fast (much faster) than mpeg2enc and the normal VCD preset
-It has better results (image looks much nicer)

Disadvantages :
-It cannot letterbox the movies, so it works correctly (I mean for playback on DVD standalone players) only for 4/3 sources
-It is not fully VCD compliant : depending on the player, you get randomly not in-sync sound, which re-syncs if you press "pause" and "play" again

As I really like this encoding (faster and better), I was wondering :

(HERE'S tHE QUESTION)

- with the fast mpeg1 option chosen, what makes the mpeg1 output file so different from a standard mpeg1 compliant VCD file ?
- I saw the sound is 48000 hz instead of 44100 which is in the standard : by demuxing and remuxing with a 44100 hz mp2, does it make it VCD compliant ?
- is there something different IN the video output ? (GOP etc..) ?

Thx for any hint.

[major]

- with the fast mpeg1 option chosen, what makes the mpeg1 output file so different from a standard mpeg1 compliant VCD file ?

It is VBR instead of CBR (Toast wil refuse that), and timestamps seem not always correct.

- I saw the sound is 48000 hz instead of 44100 which is in
the standard : by demuxing and remuxing with a 44100 hz mp2, does it make it VCD compliant ?

If source is a DVD then 48Khz leads to better sync with the ffmpeg resampler, though not standard, many players accept it.

- is there something different IN the video output ? (GOP etc..) ?

Not really, apart from what said above.