Keeping abreast of the terminology and concepts that surround video encoding can be daunting.
The successor to H.264, H.265 or HEVC, is fast becoming ubiquitous, thanks to the proliferation of 4K content.
Like any digital technology, change is constant in the video codec world. Understanding the basics around where we’ve been and where we are headed, can sometimes help video distribution decisions within your ministry or organization.
The following information will help guide you through the basics of what you should know, dispel common myths along the way, and predict future trends.
So, let’s take a look.
What is a video codec and what does it do?
The term “codec” is a portmanteau of the words enCOding (coding) and DECoding, describing a process for compressing and decompressing video or media as data for transfer over the internet, using Internet protocol, or IP.
For video engineers, a codec usually refers to the compression standard used by a video encoder, decoder or transcoder (hardware and/or software).
Why is video compression necessary?
Transporting and storing uncompressed video over the internet or in the cloud would require a colossal amount of data to be sent over a connection, along with needing significant storage, which comes with a cost. This was glaringly evident during the early “dial-up” days of the web.
Given the constant struggle for bandwidth efficiency, video compression significantly reduces required bandwidth, making it possible for real-time video streams or files to be easily transmitted across constrained networks. Video compression algorithms such as H.264/AVC or H.265/HEVC reduces raw content data by as much as 1,000 times, making video transfer more efficient and affordable.
Video compression 101
Compression techniques are used extensively across all elements of today’s computer and networking architectures, for efficient transport, storage and distribution.
The goal of a video codec is to intelligently reduce the size of video content, i.e., the total number of bits needed to represent a given image or sequence, while simultaneously maintaining picture quality.
Video compression is commonly performed by a codec’s algorithm or formula for determining the best way to compress the data.
There are several different codecs and methods of compression, but the basic concepts remain the same.
Most codecs use “lossy” compression methods which, at a high level, means that when a video is compressed, some redundant spatial and temporal information is reduced. “Lossless” compression is sometimes used when the goal is to reduce file and stream sizes by only a slight amount, in order to keep picture quality identical to the original source.
Spatial reduction or intraframe compression, physically reduces the size of the data by selectively removing parts of the original data in a video frame. Temporal reduction or interframe compression, significantly decreases the amount of data needed to store a video frame, by encoding only the pixels that change between consecutive frames in a sequence.
By grouping multiple frames within a group of pictures, or GOP, interframe compression is the most common approach for video, as it can significantly reduce file and stream sizes.
Within the context of live video streaming, a video bitrate is the number of bits that are processed within a unit of time and is commonly measured in bits per second. In general, a higher bitrate will accommodate higher image quality in the video output.
When compressed to the same bit rate, video in a newer codec such as HEVC for example, will be significantly higher quality than an older codec such as H.264. Conversely, HEVC can deliver the same video quality at a lower bitrate than H.264.
Current video codec options
MPEG-2, is the precursor to H.264 and HEVC, has been around since the 1990s and through the (Moving Picture Experts Group) was responsible for pioneering video encoding at the time with digital television and DVDs. Its compression algorithm allows for high quality, but has less sophisticated compression algorithms, as it was designed for the available compute power at the time.
While MPEG2 video encoding is slowly being phased out, in favor of new encoding standards, it’s still used by ministries for over the air terrestrial (traditional, cable and satellite TV) broadcast systems, such as ATSC, DVB-C cable systems.
H.264/AVC (Advanced Video Coding)
For high-quality video streaming over the internet, H.264 has been widely adopted and is estimated to make up the majority of multimedia traffic.
H.264 has a reputation for excellent quality, encoding speed and compression efficiency. The first version of the standard was completed in 2003, and although extensions of its capabilities have been added in subsequent editions, it’s generally considered to be an aging compression scheme. As the demand for higher video resolution continues, further efficiencies are required.
H.265/HEVC (High Efficiency Video Coding)
The successor to H.264, H.265 or HEVC, is fast becoming ubiquitous, thanks to the proliferation of 4K content. At an identical level of visual quality, HEVC enables massively improved compression allowing video to be compressed at half the bitrate of H.264, making it twice as efficient.
When compressed to the same bitrate as H.264, HEVC delivers significantly better visual quality. Video players available for current browsers’ ecosystems have yet to reach sufficient adoption rates, and are not yet delivering mass distribution of HEVC livestreams.
Developed by Google and used by YouTube, VP9 is a royalty free and open source codec which offers fewer benefits than HEVC. In terms of features, VP9 is weak in several key areas and with limited commercially available real-time VP9 encoders, it has little appeal as a contribution format for ministry.
At first glance, AV1, developed by the Alliance for Open Media (OPM) shows great promise as a new open and royalty-free standard. However, initial test deployments require significantly more computational power to manage the additional complexity compared to HEVC. For the moment, it is a work in progress and there are simply not enough details available to predict whether the broadcast industry, as well as device manufacturers, will adopt AV1 as a standard video codec.
Looking to the future
VVC (Versatile Video Coding) is a next generation compression standard, following on the footsteps of HEVC, and is currently in an early development phase. VVC is focused on achieving 30 percent better compression efficiency compared to HEVC. With the first hardware implementations slated for mid-2021, it remains to be seen what the future holds for VVC.
Which codec is the best one for you?
You may have heard of the so-called wars, where codecs are supposedly battling it out to take the top spot. But the fact of the matter is that it simply boils down to the available bandwidth, demands of the target applications and viewing devices in which it will be used.
For ministries focused on live video workflows that bring value to broadcast contribution and distribution, HEVC is a solid choice. It’s baked into billions of chipsets, from encoders and TVs, to set-top boxes and mobile devices, making it a popular and realistic option for contribution and transcoding.
For established digital broadcast systems, H.264 is still required, depending on the OVP and embedded players used. In most cases, broadcast engineers need to support both codecs.