The truth on file info / metadata

[Case]

I was trying to compare the DivX AVI to DVD encoding of ffmpegX (by me) and MainConcept MPEG Encoder on a PC (by a friend). We agreed on 6000 kbit/sec CBR.

Source file: VIDEO: mpeg4 (fourcc DX50), 640x360, 25.00 fps. AUDIO: mp3, 48000 Hz, stereo, 132 kb/s. TIME: 00:17:35

After encoding with ffmpegX (fast DVD), the muxed mpeg file is 383.3 MB, roughly half (!) the size expected of 6 Mbps. The info line states the video is 6000 kbps. The Info button says 6 Mbps. The info line states the audio is 448 kbps, 48 KHz. The Info button says 384 Kbps, 48 KHz. (Two pass encoding adds 0.9 MB.)

After encoding with ffmpegX (DVD preset (mpeg2enc, CBR checked)), the muxed mpeg file is 335.8 MB, roughly 40% of the size expected of 6 Mbps. The info line states the video is 6000 kbps. The Info button says 6 Mbps. The info line states the audio is 448 kbps, 48 KHz. The Info button says 320 Kbps, 32 KHz.

The AC3 files for both encodings are identical in size, suggesting 448 kbps (56.3 MB/1055 sec).

- Can I encode at a true 6 Mbps with ffmpegX?
- If the encoder decided to encode the video at a lower bitrate, how come the Info (header?) states 6 Mbps?
- How come the info line on top says something different for the audio than the Info button?
- Are these bugs or limitations?

[major]

mpeg-2 encoding with ffmpegX is VBR. Decreasing the quantizer can increase the file size. The header info is the nominal max bitrate.