In DVD recording, a standard, single layer, 4.7 GB disc holds up to 2 hours of video at DVD quality. All commercial movie DVDs hold about 5GB per layer - which each layer holding about 133 min. If you buy a movie DVD that has a 2 hour movie, plus an hour or so of extra features, this means that the disc has more than one layer. Some DVDs are also dual-sided.
All currently available DVD players and recorders can play back commercial discs with more than one layer. However, some older players (pre-1999) may not be able to in all cases. Also, there are DVD recorders that can now record on Dual Layered Discs. However, for this article, I will be referring predominantly to single layered discs, since these are most commonly used.
DVD Recording Modes - Not Speeds
One thing to keep in mind that that DVD recorders do not have recording speeds, like a VCR does. The disc rotates in a set manner, either at constant static rotation rate or at a constant accelerated rotation rate throughout the recording process (depending on disc format).
DVD Record Modes and Video Compression
What changes when you want to record a program longer than 2 hours is that the DVD recorder has to compress the video at a higher ratio in order to fit more time on the 2-hour disc.
In other words, by compressing the video into smaller file sizes, you can fit more recording time (4, 6, or 8 hours) on the same, 4.7 GB 2-hour-sized disc. Typically, DVD recorders have 1, 2, 4, and 6 hour record modes. Some DVD recorders also feature other modes, such as 1.5, 3, 8, and even 10 hour modes.
However, keep in mind that recordings made at a longer mode length that 2 hours will be lower in quality due to the increased compression. In addition, especially with recordings that are longer than 4 hours, the increased compression not only affects the video quality, but can also affect playback on some DVD players. With increased compression, the disc is harder to read and may cause skips and freezes on some DVD players.
How Disc Writing Speed Factors Into DVD Recording
This is where things can get very confusing for the consumer. When you buy a blank recordable DVD, on the label it not only refers to the disc size and record mode time, but also refers to Writing Speed. The disc label may indicate a 2x, 4x, 8x, or higher Writing Speed capability.
What Writing Speed refers to is the how fast video or other types of computer data can be written to the DVD disc from a hard drive or another disc.
In the case of a PC or MAC, this means you can copy a video or data file that you have previously recorded on your hard drive to a particular DVD disc, or, from one disc to another, that you have placed in your DVD-writer, at a high rate of speed.
For example, you can copy a 2 hour long video that you have recorded on your hard drive to a DVD in 15 minutes, if the DVD writer and DVD disc supports an 8x writing speed. By the same token, if you have a DVD recorder that also has a hard drive, you would be able to copy the same 2 hour video to a DVD disc at the same 8x speed, provided the DVD recorder and Disc support it.
In other words, DVD writing speed, at least conceptually, is analogous to the high-speed dubbing functions on most Dual-Well Audio Cassette decks, Audio Cassette/CD recorder combos, or Dual-Well CD Recorders that allow the user to copy from tape and/or CD to another tape and/or CD at a 2x or 4x higher-than-normal speed. This also applies to making copies of CDs on a PC, the faster the writing speed of the drive and the disc, the quicker you can copy from one disc to the next. This is also commonly referred to as Tape or Disc Dubbing Speed.
DVD recorders do not have recording speeds, like a VCR, but Recording Modes. DVD Recording modes can be used when recording from outside sources, such as a VCR or Camcorder. The DVD Recording Modes enable the user to put more video time on a DVD disc by increasing the amount of compression in the video signal, not changing the rotation speed of the disc.
The downside to putting more video time on a DVD disc is a loss of quality in the recorded video and possibly decreasing playback compatibility on other DVD players.
Disc Writing Speed, on the other hand, has no relation to how much time you can put on a DVD disc, but refers to how fast you can dub from a computer or DVD recorder hard drive, or from another disc to a recordable DVD disc. Disc Writing Speeds are used when making copies of video or data from internal pre-recorded sources, residing on a PC, DVD Recorder hard drive, or another disc.