There are lots of tape formats, with more coming out all the time. We are increasingly moving towards a tapeless environment, but we are still far from it. Around 95% of the projects I receive are delivered on one tape format or another, so it is still important to know the strengths and weaknesses of each format, because at some point in the post production line you are going to want to record to one of them. In this post I am going to cover the important specs to look at in a tape format, and in future posts I will cover the most important formats in greater detail, paying particular attention to how they should be used.
Below is a chart I pulled together listing the most popular tape formats and their relevant specs. It is broken into 2 sheets to better fit the width of the page. You can also download a PDF of it by clicking here.
There are only two uncompressed tape formats and neither is in common use anymore because they are so expensive. That leaves us with lightly and heavily compressed tape formats. I will go over compression in more detail in another post, but in short compression is bad because it throws away information; information that you may need later on. The best thing you can do is to be aware of this limitation, and use a format that is less compressed than the alternatives. Much like generation loss in the analog world, there is a generation loss in the digital world because of compression. Each successive copy will be further away from your original video. If you take a look at the above chart you can see the level of compression in the Compression Ratio column. The higher the first number the greater the compression. A related spec is the data rate, which is the amount of data, or information, the tape can record per second. The greater the data rate the less compression is needed.
There are other things that affect image quality such as Resolution and Bit-Depth. The resolution is the number of pixels measured horizontally and vertically that make up a frame. Some of these tapes are standard definition and record the full 720×480 image size, and others are high definition, not all of which record the full 1920×1080 image size. Because of the lower data rates of some of these tapes manufacturers reduce the amount of information by reducing the resolution. The most common way to do this is to use a resolution of 1440×1080 with rectangular pixels that are then stretched up and scaled on playback to create the regular 1920×1080 square pixels.
Bit-Depth is the number of different colors that are included in the world of possible colors recorded onto the tape. The Bit-Depth also affects the dynamic range, the range of lights to darks between white and black. Think of it as how many different crayons are in your crayon box. You can save a lot of space in your backpack by carrying the 24 color crayon box instead of the 120 color crayon box, but when it comes time to color you have many fewer options and gradations. 8-bit, 10-bit, it sounds like a small difference, but 8-bit gives you 256 levels per channel, and 10-bit gives you 1024 per channel, that’s 4 times more per channel. This makes a big difference when you want to start changing colors, contrast, and brightness in post. The 8-bit will begin to band and fall apart much earlier than the 10-bit.
So what does all this mean? It means choose carefully, and get the best video master you can afford, as it will affect everything downstream considerably. It does not mean that shooting to one of these highly compressed formats is necessarily bad though. If you choose to shoot to a highly compressed format like DV or HDV don’t go back to those tape formats if you can help it. Shoot in cheap highly compressed formats and finish and master to lightly compressed formats, like Digibeta, D5, HDCAM (sort of), or HDCAM SR.