Two separate questions
Color in video depends on two things that are easy to confuse. A color space defines which colors can be described, meaning the range or gamut, along with how numbers in the file map to light. Bit depth defines how finely the steps between those colors are divided. A wide color space with low bit depth can show strong colors in coarse steps, and a narrow space with high bit depth can show smooth steps across a limited range.
Rec.709: the long-standing standard
Rec.709, also written BT.709, is the standard for high-definition video. Most standard-dynamic-range HD content, including most online video, is produced for it. It uses the same primary colors as sRGB, the common standard for computer screens and web graphics, which is a large part of why video and web content look broadly consistent on ordinary displays.
Because Rec.709 is well established, almost every display can reproduce it reasonably well. That is why it is the usual safe choice when the destination is unknown.
Rec.2020: a wider target
Rec.2020, also written BT.2020, was defined for ultra-high-definition television. Its primaries are much more saturated, so it describes a considerably larger range of colors than Rec.709. Important caveat: a file tagged as Rec.2020 does not necessarily contain colors that fill that space, and many consumer displays cannot reproduce all of it. In practice, content is often mastered in a smaller space such as DCI-P3, which is used in digital cinema and many recent phones and monitors, and then carried inside a Rec.2020 container.
Wide gamut matters most for strongly saturated colors such as vivid greens and deep reds. For everyday footage with natural tones, the difference can be subtle. It also goes hand in hand with high dynamic range, which is why the two are often introduced together.
What bit depth means
Digital video stores each color channel (red, green and blue, or an equivalent) as a number. Bit depth is the number of bits used per channel, and it sets how many distinct levels are possible.
- 8-bit gives 2 to the power of 8, which is 256 levels per channel. Across three channels that is 256 x 256 x 256, or about 16.7 million combinations.
- 10-bit gives 1,024 levels per channel, and 1,024 x 1,024 x 1,024 is about 1.07 billion combinations.
Four times as many levels per channel means each step between shades is much smaller. For standard video, 8-bit is common for delivery, while 10-bit is common in higher-quality capture, editing and HDR delivery. Note also that in typical video, not every code value is used for picture: the standard “limited range” reserves some values at each end, so 8-bit video uses fewer than 256 usable levels.
Banding
The visible symptom of too few levels is banding: smooth gradients such as a clear sky, fog or a studio backdrop break into visible stripes. It tends to show up when a gradient spans a small tonal range, or when heavy compression removes subtle differences. Higher bit depth gives encoders more headroom to keep those gradients smooth, though compression settings, and especially a low video bitrate, still matter.
Banding becomes more noticeable in HDR, where a gradient stretches across a larger brightness range, which is one reason HDR delivery uses at least 10 bits.
Aggressive grading can also expose banding. When you push contrast or saturation in 8-bit footage, you stretch levels apart, and gaps appear. Shooting at a higher bit depth leaves more room, a point that matters in color grading.
Chroma subsampling
Related but distinct is chroma subsampling, written as 4:2:0, 4:2:2 or 4:4:4. Video often stores brightness at full resolution and color at reduced resolution, because the eye is more sensitive to detail in brightness. 4:2:0 is typical for delivery, with 4:2:2 and 4:4:4 keeping more color detail, which helps when keying green screens or handling fine colored text.
Where things go wrong
Most color problems come from mismatched assumptions:
- A file is tagged with one color space but displayed as if it were another, producing washed-out or oversaturated images.
- A wide-gamut or HDR file is shown on a display that handles it poorly, causing dull or clipped colors.
- A screen is not calibrated, or is set to an aggressive picture mode.
- Different software interprets the same file differently.
Correct metadata tags help, and the article on video metadata covers how such tags are stored. Display settings matter too. Even careful work is only an approximation of what a given viewer sees, since screens differ.
Practical guidance
For most online projects, working and delivering in Rec.709 with 8-bit or 10-bit video is sensible, with 10-bit preferred when you plan heavy grading. If you shoot in a camera’s logarithmic profile, which spreads brightness in a way that preserves detail, 10-bit capture is usually advised, and the footage needs conversion in editing. Check the platform’s current requirements before exporting for wide-gamut or HDR delivery, and look at the result on more than one screen. Settings for the final file are discussed in the notes on export settings.