Virtual Reality (VR) and 360 Videos 101 — A Beginner’s Guide
VLC just announced its plans to support 360º video. YouTube and Facebook already do. Everyone seems to be jumping on the 360º bandwagon. Why? Because 360º video is the gateway drug to virtual reality.
Compared to 3D worlds, 360º videos are fairly easy and cheap to create. Cameras are built to create them at a touch of a button, and where a single camera lacks, rigs with multiple cameras can step in to fill the literal visual holes. However, as with all content, 360º videos comes in a variety of quality. How can you determine quality? Look for and test the following:
1. Device Type
As of today, there are three categories of viewing devices for VR: mobile VR, desktop VR, and console VR. Mobile VR includes mobile-powered VR headsets such as Google Cardboard, Daydream View and Samsung Gear VR, as well as stand-alone VR headsets which we see Facebook, Qualcomm, and a few others that have yet to announce. Desktop VR means the device is powered by desktop PC. This category includes products like Oculus Rift and HTC Vive. At last, console VR means the device is powered by a game console, like PlayStation VR.
2. Device Specs
With new devices being released every day, it’s important to keep in mind the capabilities of a device before judging the quality of a 360º video. Each device will have its own resolution, and keeping up with the current trend, you would assume each eye would see half of that. You then also have to take into consideration the field of view, which is how much of the entire 180°x 360° view you’ll see at one time.
3. Content Resolution
For most people, when it comes to video content, resolution comes first to mind. However, unlike a TV, resolution for 360º video is a bit more complicated. Content is stretched to fit 180° vertically and 360° horizontally and then split between your two eyes, and on top of that, your field of view is limited to around 100 degrees. Currently, some viewers might have the perception that visible section is in 4K resolution, when in actuality, the whole 360º sphere is in 4K and the visible section is just one-fifth or sixth of that resolution. In most cases, that means a minimum of 4K resolution is needed to let you see DVD quality content (nearly 720P in a monoscopic scenario). With a minimum of 6k to get close to HD or 1080P, and a minimum of 8K to get close to UHD or 4K.
Due to the unique nature of 360º videos, VR requires video resolution to be at least 4K to achieve an okay level of viewing experience. A 6K to 8K resolution would be much better, raising the bar with the better VR experience compared to regular video. However, today in the U.S. most home WiFi and mobile internet can only support the streaming of 720P to1080P videos. The bandwidth gap here severely prevents user experience improvement. This is where Visbit’s technology plays a critical role to bridge the gap.
4. Stereoscopic versus Monoscopic
Stereoscopic videos give you depth by layering content in the foreground and the background. However, most content you will find today will be monoscopic. Why? Because stereo is hard. When it comes to 360º videos, stitching, that is the process of digitally tying frames together, is a vital part of creating a flawless and immersive reality. Stereo videos are very unforgiving when it comes to stitching errors, and since you’re using two cameras to create the video, you now have four times as many chances to mess up (2 cameras for each eye). When comparing content, make sure you’re not comparing stereo to mono.
Motion-to-Photon Latency
There are a few types of “latency” terms in virtual reality. The most used “latency” term is the Motion-to-Photon latency. This type of latency refers to the time it takes an image to match the movement of a user. In an ideal world, this time would be at 0, and VR motion sickness would be a thing of the past. However, things like device, bandwidth, content loading and streaming, and content type all affect latency. Today on Desktop VR, most manufactures desire to reach 11ms with 90HZ refresh rate. On Mobile VR, manufactures desire to reach 16ms with 60HZ refresh rate. Not only does the headset need to achieve this standard, but also the video playing need to do so. However, a higher latency could cause nausea and ruin an otherwise great VR experience. A quick test to check the latency can be done by quickly turning your head. If the video is choppy or in a worst case scenario, the video view is turning together with your head, a latency issue existing. Different people have different sensitivity to latency. Those who easily experience motion sickness typically have a lower tolerance to Motion-to-Photon latency.
There is another “latency” concept shows up when we talk about foveated streaming or foveated rendering, a new type of streaming technologies designed for 360o videos. Both Oculus Dynamic Streaming and Visbit “View Optimized Streaming” belong to foveated streaming. In foveated streaming, only the visible section of a 360º video would be streamed in high resolution while the nonvisible section is streamed in low resolution. When a user turns their head, that low resolution stream would be switched with the high resolution stream. This view-switch latency between low resolution and high resolution is another latency you would need to know.
6. Streaming
A lot of today’s VR content is accessed through large downloads thanks to the high resolution needs of 360º VR videos. However, this takes time and storage. For improved 360º content, a cheap, fast, and reliable stream is indicative of quality. Streaming, like most things in VR, can be complicated, but there are some things that can quickly indicate a quality stream:
- Bitrate: How many bits per second are stored in the video? For a 4k 360º VR video, you would look for about 11,000–12,000kbps considering that most 360º videos are quite static with few cuts
- Frame Rate: How many frames are shown in a second? The more, usually the better. You want a minimum of 30fps for watching VR videos, with many people pushing for 50–60 for hyper-realistic videos.
- Encoding: Streaming requires compression, which then requires decompression. With a good codec, you’re seeing smaller video sizes of higher quality
- High Resolution, Low Latency: We’ve already talked about these two (refer to Why do all the 360º VR videos today look so pixelated?), but you want to ensure that the stream keeps the high resolution of the content without increasing latency.
In the end, there really isn’t an easy comprehensive trick to amazing 360º VR video. We’ve only done a cursory overview of a few of the aspects of 360º VR videos, and even each of these aspects can be delved into deeper.
Here at Visbit, we’re concentrating on optimizing 360º VR video streaming for improving not only the quality of the content but also the manageability of your server and your wallet. You can learn more about what we do and sign up for our newsletter here.
