Video Transcoding Services: Which Video Bitrate for Mobile Devices?
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Video transcoding is the process of making a video that’s been encoded in one format and converting it into another format. Video transcoding services are used to offload this processing overhead to a service provider that specializes in this task. Some common providers of video transcoding services include Encoding.com and Zendesk. Several online video platforms such as Dacast incorporate video transcoding services into live streaming and video hosting offerings.
When considering transcoding services, it’s important to get the settings just right. Incorrect settings can translate into a poor-quality or even unwatchable video. Because many people today use so many different devices, proper settings are even more essential than just ensuring the acceptable video quality.
What is transcoding?
Before we understand transcoding, we have to understand video compression.
The natural format of a video is “uncompressed.” This means that each frame of the video—30 frames per second is standard—is recorded as a standalone image. However, uncompressed video results in HUGE file sizes that are impractical for all but professional users.
As a result, most video cameras actually record compressed formats. This means that some data is thrown out to reduce file sizes. Compression is achieved through mathematical algorithms, but the basics are easy to understand. Let’s say the whole frame of your video is black for two seconds—for example, a subject could be entering a dark room. An uncompressed video would store all 60 frames as individual images. Compression enables you to save space by instead saying “render all pixels black for the next 60 frames.” In practice, this causes some loss of quality.
There are a variety of different compression schemes used for reducing the file size of the video and then uncompressing it for playback (codecs). The most common is H.264, which is supported on almost every mobile device. This is gradually being replaced by H.265, but still remains widely supported.
Essentially, video transcoding is the process of decoding or decompressing a compressed video file, then re-encoding it into another format. This is often necessary during the course of video production for many reasons. For example, you may wish to reduce file sizes further or change the resolution of the video. It may also be necessary to use an alternate format to reach users on a specific device or operating system.
Setting the correct video bitrate for mobile devices
Mobile device users have a few unique requirements. For one, data is precious. There are almost no users left on unlimited data plans. Every megabyte goes against their limit. Furthermore, web connections in mobile environments can vary dramatically over short spans of time, so streaming video has to be properly transcoded for the mobile environment. Due to this, minimizing file sizes for mobile video is essential. This involves reducing the bitrate, or the amount of data per second in a streaming file.
At the same time, processing power and screen quality on mobile are advancing. Retina and Ultra-HD (4K) screens are becoming common on smartphones. Poor video quality is especially apparent on screens of this quality. Screen size is increasing too. The norm for smartphone screen sizes these days is around five inches. In this larger environment, video that is too compressed or too small delivers a subpar viewing experience.
The diverse mobile ecosystem
Fortunately for consumers (but unfortunately for broadcasters), there is a wide range of mobile devices on the market. It’s great for choice, but it also means that older devices don’t support the newer formats and file sizes that work best on more modern phones and tablets. With that said, here are our recommendations for a few different categories of users.
To reach every device, regardless of age:
- Video bitrate: 400 kbps or less
- Frame size: 320 x 240
- Frame rate: 30 fps
- Audio bitrate: 64 kbps or less
These settings will reach just about every mobile device around, including old iPods, Blackberries, and more.
To reach almost every device, but deliver better quality:
- Video bitrate: 1100 kbps or less
- Frame size: 480 x 270 pixels (very low-end devices) or 640 x 360 pixels (plays better on iPhone 4G and Droid phones)
- Frame rate: 30 fps
- Audio bitrate: 128 kbps or less
This should reach nearly every smartphone and Blackberry, but is too small for more modern phones.
To reach higher-end smartphones:
- Video bitrate: 3500 kbps (WiFi), 2000 kbps (cellular) or less
- Frame size: 1280 x 720 or 960 x 640
- Frame rate: 30 fps
- Audio bitrate: 160 kbps or less
These settings will work best if your audience uses iPhone 4G and above or modern Androids from the Nexus, Galaxy, and Droid series.
H.264 profile settings
Of course, choosing the right video bitrate for mobile isn’t everything. That’s why we included frame size, frame rate, and audio bitrate information here. However, another important consideration is the H.264 profile you use. In general, we recommend the “baseline” profile for all mobile devices. It ensures backward compatibility and delivers good quality.
Delivering video to mobile devices is essential, but it requires high quality coupled with minimal file sizes. The settings we’ve shared here should help you make the best of this situation, delivering excellent video to your viewers.
Any OVP (online video platform) should include video transcoding services in its offerings. You can use video transcoding to make multiple versions of each video file you host. That way, viewers can automatically be redirected to the version that works best for them.
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