As anyone involved in the broadcast industry will tell you, the terminology used in this business is expansive. With great leaps made in video technology over the last few decades, it can be difficult to fully understand what specific concepts are referring to, especially as they evolve over time. This post is all about two often confused terms: aspect ratio and video resolution.
Though both pertain to how a picture is viewed, they each have significantly different effects on that picture and whatever screen it may be viewed on.
Typically expressed in a width to height format (W:H), aspect ratios represent the area of space an image is presented in. We can really go down the rabbit hole with this concept (probably for video resolution as well), but I’ll limit things to some of the more common aspect ratios out there. For a majority of viewers, there are only two formats to really worry about: 4:3 and 16:9.
Older model televisions use a 4:3 aspect ratio, while newer models stick with 16:9. Movies, however, play in 21:9, which is pretty rare to find in a consumer-grade television. Other formats exist, but since the 4:3 and 16:9 aspect ratios are generally standardized throughout the industry, it’s unlikely you’ll encounter them.
What happens when you play a video encoded in one aspect ratio on a monitor of a different size? Black bars:
This is also why you’ll sometimes get black bars on the top and bottom of movies you watch at home, even if you have a “widescreen,” 16:9 television. The movie itself was encoded in 21:9, meaning your output needs to shrink just a bit to fit the whole image on screen. Adjustments can be made to avoid the black bar scenario, but that means either trimming portions of the image, or stretching it to fill the screen, causing unsavory proportions.
It’s true there is a correlation between aspect ratio and video resolution, but not as much as you might think. Standard definition video falls within the 4:3 boundaries of aspect ratio, but that doesn’t mean you can’t have a high definition video file in the same aspect ratio, nor does it mean SD video is limited to 4:3. Aspect ratio merely represents how a video is displayed; video resolution, on the other hand, has a much greater effect on image quality.
Video resolutions are commonly represented as dimensions: 720 x 480, 1280 x 720, 1920 x 1080. These are specifically referring to the total number of pixels being displayed on screen. So 720 x 480 = 345,600 pixels, while 1920 x 1080 = 2,073,600 pixels. This means that 1920 x 1080 (or “full HD”) displays six times the pixels on the screen than 720 x 480 (standard definition).
What’s more, in standard definition video, there tends to be a variation in resolutions across broadcasting standards. While 640 x 480 is popular for streaming, standards of 704 x 480, or 720 x 480 are used for broadcast, along with additional resolutions for PAL video (not covered in this article). This is in part due to a difference in pixel shape: SD broadcast uses a non-square pixel format, while most digital media uses square pixels. This is referred to as “pixel aspect ratio” and is another one of those “rabbit hole” situations that I could write an entire article about.
|Video Resolution||Common Name||Associated Aspect Ratio|
|720 x 480 (or 704 x 480)||SD||4:3|
|1280 x 720||HD Ready||16:9|
|1920 x 1080||Full HD||16:9|
Side note: what about the little “p” or “i” at the end of the resolution (i.e. 1080i or 720p)? Those stand for “progressive” or “interlaced” scanned lines, respectively. They describe how different lines of pixels are presented on a screen. With an interlaced scan, lines are displayed horizontally starting with odd lines, and then moving on to even for every frame. Progressive scanned lines are displayed one after another in order.
Understanding all of these different resolutions and aspect ratios can be a pretty daunting task. It’s even more of a headache when you’re a broadcaster working with both HD and SD resolutions, along with 4:3 and 16:9 aspect ratios. Keeping this in mind, we gave the UltraNEXUS-HD the ability to auto scale any signals, letting broadcasters work with HD video files while still playing out on an SD channel. Check out this article from John for more information.
Hopefully this quick run through of aspect ratios and video resolutions clears up any confusion between the two without going into too much depth. Have additional questions about your video files? Check out our description of the different elements that go into them, or give us a call at (800) 243-5589 and chat with our solution specialists.
Aaron is an engineer and network manager for the company and is responsible for web interface development of many LEIGHTRONIX video encoder products. He is also responsible for development and maintenance of the VieBit® streaming content service as well as the architecture and maintenance of in-house servers.
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