[2.4] Is CD compatible with DVD?

This is actually many questions with many answers, covered in the following sections.
[Note the differentiation between DVD (general case) and DVD-ROM (computer data).]

Yes. All DVD players and drives will read audio CDs (Red Book). This is not actually required by the DVD spec, but so far all manufacturers have made their DVD hardware read CDs.

On the other hand, you can't play a DVD in a CD player. (The pits are smaller, the tracks are closer together, the data layer is a different distance from the surface, the modulation is different, the error correction coding is new, etc.) Also, you can't put CD audio data onto a DVD and have it play in DVD players. (Red Book audio frames are different than DVD data sectors.)

Yes. All DVD-ROM drives will read CD-ROMs (Yellow Book). Software on a CD-ROM will run fine in a DVD-ROM system.

However, DVD-ROMs are not readable by CD-ROM drives.

Sometimes. The problem is that most CD-Rs (Orange Book Part II) are "invisible" to DVD laser wavelength because the dye used to make the CD-R doesn't reflect the beam. Some first-generation DVD-ROM drives and many DVD players can't read CD-Rs. The formulation of dye used by different CD-R manufacturers also affects readability. That is, some brands of CD-R discs have better reflectivity at DVD laser wavelength, but even these don't reliably work in all players.

The common solution is for the DVD player or drive to use two lasers at different wavelengths: one for reading DVDs and the other for reading CDs and CD-Rs. Variations on the theme include Sony's "dual discrete optical pickup" with switchable pickup assemblies with separate optics, dual-wavelength lasers (initially deployed on Sony's Playstation 2), Samsung's "annular masked objective lens" with a shared optical path, Toshiba's similar shared optical path using an objective lens masked with a coating that's transparent only to 650-nm light, Hitachi's switchable objective lens assembly, and Matsushita's holographic dual-focus lens. The MultiRead logo guarantees compatibility with CD-R and CD-RW media, but unfortunately, few manufacturers are using it.

Bottom line: If you want a DVD player that can read CD-R discs, look for a "dual laser," "twin laser," or "dual optics" feature.

An effort to develop CD-R "Type II" media compatible with both CD and DVD wavelengths was abandoned.

DVD-ROM drives can't record on CD-R or any other media, but a few combination DVD-ROM/CD-RW drives can write to CD-R and CD-RW. Most newer recordable DVD drives (see 4.3) can also record on CD-R or CD-RW.

CD-R burners can't read or write DVD discs of any kind.

Usually. CD-Rewritable (Orange Book Part III) discs have a smaller reflectivity difference, requiring new automatic-gain-control (AGC) circuitry in CD-ROM drives and CD players. Most existing CD-ROM drives and CD players can't read CD-RW discs. The OSTA MultiRead standard addresses this, and some DVD manufacturers have suggested they will support it. The optical circuitry in even first-generation DVD-ROM drives and DVD players is usually able to read CD-RW discs, since CD-RW does not have the "invisibility" problem of CD-R (see 2.4.3).

Most newer recordable DVD drives (see 4.3) can also record on CD-R or CD-RW.

CD-RW burners can't read or write DVD discs of any kind.

Sometimes. It's not required by the DVD spec, but it's trivial to support the Video CD (White Book) standard since any MPEG-2 decoder can also decode MPEG-1 from a Video CD. About two thirds of DVD players can play Video CDs. Most Panasonic, RCA, Samsung, and Sony models play Video CDs. Japanese Pioneer models play Video CDs but American models older than the DVL-909 don't. Toshiba players older than models 2100, 3107, and 3108 don't play Video CDs.

VCD resolution is 352x288 for PAL and 352x240 for NTSC. The way most DVD players and Video CD players deal with the difference is to chop off the extra lines or add blank lines. When playing PAL VCDs, the Panasonic and RCA NTSC players apparently cut 48 lines (17%) off the bottom. Sony NTSC players scale all 288 lines to fit.

Because PAL VCDs are encoded for 25 fps playback of 24 fps film, there is usually a 4% speedup. Playing time is shorter, and the audio is shifted up in pitch unless it was digitally processed before encoding to shift the pitch back to normal. This also happens with PAL DVDs (see 1.19).

All DVD-ROM computers can play Video CDs (with the right software).

Standard VCD players can't play DVDs.

Note: Many Asian VCDs carry two soundtracks by putting one language on the left channel and another on the right. The two channels are mixed together into babel on a stereo system unless you adjust the balance or disconnect one input to get only one channel.

For more on Video CD, see Russil Wvong's Video CD FAQ.

Not generally. Super Video CD (SVCD) is an enhancement to Video CD that was developed by a Chinese government-backed committee of manufacturers and researchers, partly to sidestep DVD technology royalties and partly to create pressure for lower DVD player and disc prices in China. The final SVCD spec was announced in September 1998, winning out over C-Cube's China Video CD (CVD) and HQ-VCD (from the developers of the original Video CD). In terms of video and audio quality, SVCD is in between Video CD and DVD, using a 2x CD drive to support 2.2 Mbps VBR MPEG-2 video (at 480x480 NSTC or 480x576 PAL resolution) and 2-channel MPEG-2 Layer II audio. As with DVD, it can overlay graphics for subtitles. It's technically easy to make a DVD-Video player compatible with SVCD, but it's being done mostly on Asian DVD player models. The Philip's DVD170 player can be upgraded (using a special disc) to play SVCD discs.

SVCD players can't play DVDs, since the players are based on CD drives.

See Jukka Aho's Super Video CD Overview and Super Video CD FAQ for more info.

Sometimes. Because Picture CDs and Photo CDs are usually on CD-R media, they suffer from the CD-R problem (see 2.4.3). That aside, some DVD players can play Picture CDs. Only a few can play Photo CDs.

Most DVD-ROM drives will read Picture CDs or Photo CDs (if they read CD-Rs) since it's trivial to support the XA and Orange Book multisession standards. Picture CDs are designed to work with Windows. Photo CDs require specific support from an application or an OS.

Photos can be put on recordable DVDs using the DVD-Video slideshow feature, which works on all DVD players. See 5.8.

In general, no. DVD players do not play CD-i (Green Book) discs. Philips once announced that it would make a DVD player that supported CD-i, but it never appeared. Some people expected Philips to create a "DVD-i" format in an attempt to breathe a little more life into CD-i (and recover a bit more of the billion or so dollars they invested in it). A DVD-ROM PC with a CD-i card should be able to play CD-i discs.

There are also "CD-i movies" that use the CD-i Digital Video format that was the precursor to Video CD. Early CD-i DV discs won't play on DVD players or VCD players, but newer CD-i movies, which use the standard VCD format, will play on any player that can play VCDs (see 2.4.5).

See Jorg Kennis' CD-i FAQ for more information on CD-i.

Yes. DVD players will play music from enhanced music CDs (Blue Book, CD Plus, CD Extra), and DVD-ROM drives will play music and read data from enhanced CDs. Older ECD formats such as mixed mode and track zero (pregap, hidden track) should also be compatible, but there is a problem with Microsoft and other CD/DVD-ROM drivers skipping track zero.

Only a few players, such as the Pioneer DVL-9 player and Pioneer karaoke DVD models DV-K800 and DVK-1000, support CD+G discs. Most DVD players don't support this mostly obsolete format. All DVD-ROM drives can read the CD+G information, but special software is required to make use of it.

Sort of. CDV, sometimes called Video Single, is actually a weird combination of CD and laserdisc. Part of the disc contains 20 minutes of digital audio playable on any CD or DVD player. The other part contains 5 minutes of analog video and digital audio in laserdisc format, playable only on a CDV-compatible laserdisc player. Pioneer's combination DVD/laserdisc players are the only DVD players that can play CDVs.

Standard laserdisc/CDV players can't play DVDs. (See 2.5 for more LD info.)

Not officially. MP3 is the MPEG Layer 3 audio compression format. (MP3 is not MPEG-3, which doesn't exist.) The DVD-Video spec allows only Layer 2 for MPEG audio (MP2). However, MP3 can be played any computer with a DVD-ROM drive, and many DVD players (particularly those manufactured in Asia) can play MP3 CDs. However, most DVD players can't play MP3 DVDs, because they are shortsightedly designed to only look for MP3 files on CDs. Check the player list at DVDRHelp.com for players that can play MP3 CDs or MP3 DVDs.

Yes. Pacific Microsonics' HDCD (high-definition compatible digital) is an encoding process that enhances audio CDs so that they play normally in standard CD and DVD players (and allegedly sound better than normal CDs) yet produce an extra 4 bits of precision (20 bits instead of 16) when played on CD and DVD players equipped with HDCD decoders.