50MB or 700MB - is a maximal size of CD intended for DATA.
Real maximal size of 650MB CD is: 746.9 Mb
Real maximal size of 700MB CD is: 807.5 Mb
CD consist of sectors. Each sector has 2352 bytes.
DATA CDs occupy only 87% of all sectors (700MB of 807.5MB or 650MB of 746.9MB). CDs with data and CD reading mechanisms are not faultless. That is, errors (indeed frequent errors) could be made during the reading. A single bit error could lead to a program being unexecutable or ruin an archive file. Thus, for CD-ROMs, part of each sector is devoted to error correction codes and error detection codes. The CD-R FAQ has the details, but in effect, only 2048 bytes out of a total of 2352 bytes in each sector is available for user data on a data CD. The burning mode for CD with DATA is either MODE1 or MODE2 Form1.
Audio CDs occupy each byte of all of sectors. 2352 bytes of 2352 bytes. That's why capacity of audio CD is maximal (100%, 807.5MB of 807.5MB). For audio CDs errors aren't important as for CDs with data. Audio CDs do not contain correction codes, because it's possible to interpolate from the adjacent audio samples.
VCD and SVCD CDs occupy 98.8% of all sectors. 2324 bytes of 2352 bytes. The capacity of VCD is almost maximal (797.9MB of 807.5MB or 738MB of 746.9MB). Additional space per each sector isn't used for error codes, the space is used for something other than video data (e.g., sync headers). The burning mode for VCD is MODE2 Form2.
So, as you noticed the main determinant is the burning mode of the disc. MODE2 Form2 for VCD and MODE1 for CD with DATA.
The often quoted capacities of 650MB and 700MB refer to CD-ROM capacities. Due to the fact that S/VCDs use a different burning mode where MORE of each sector is available as user data, the relatively capacities are HIGHER. Now, since S/VCDs are not composed of PURELY video tracks and have some unavoidable overheads, the actually total capacity left for video tracks is a few Mb less for each disc (about 735 Mb for 74min discs and 795 Mb for 80min discs). This is where the often quoted capacities of 740MB and 800MB come from. They are quite accurate. All these capacities are available BEFORE overburning. Overburning is where you burn MORE sectors than the disc is rated for. If you overburn, you can typically achieve about 1-2 minutes of additional capacity (depending on your drive and media).
Yeah, that's the best workaroundEin said:U can use [URL="http://www.vcdgear.com/"]VCDGear(freeware,2.4MB) to extract the MPEG from the NRG (will be <700MB) and burn it back as a VCD (DAT) using Nero.