In 2012, YouTube switched to adaptive bit rate streaming (or scaling) for its desktop player. The move reduced buffering by 20 percent and sped up the launch of new online videos. Now, the Google-owned video service is bringing the new technology to mobile and home television sets.
Andy Berkheimer, the head of engineering at YouTube and the man behind the network’s adaptive streaming effort, made the YouTube computer player automatically switch between different video quality settings based on the user's Internet connection speed.
The next target market, he told GigaOM in an interview, is mobile and home television.
“We are making it work just as it should,” Berkheimer, an MIT graduate, told the website. Optimizing video playback, he said, has been a long, difficult journey beginning six years ago when YouTube had a single default video quality at 320 x 240 — or 240p. “That was really, really grainy video,” he recalled.
After hundreds of hours of trying different algorithms on whiteboards, burning through boxes of markers, and marathon coding sessions with engineers in Cambridge and at YouTube’s headquarters in San Bruno, CA, Berkheimer and his team debuted the new player.
His team used Google’s cloud infrastructure to allow for additional codecs, bringing HD and eventually even 4K resolution video to YouTube viewers, who watch about four billion videos each month.
Adaptive bit rate streaming, which is industry-speak for switching the quality of a video in midstream, without the need to rebuffer and start over, was the answer, he said. The current YouTube player keeps close eyes on the speed and health of the user's Internet connection, he explained.
“It’s continuously monitoring the bandwidth and the throughput it is seeing,” he said. If the user is watching video on a full screen, YouTube sends more bits, as long as the Internet connection is fast enough.
The streaming works by detecting a user’s bandwidth and CPU capacity in real time and adjusting the quality of a video stream accordingly. It requires the use of an encoder which can encode a single source video at multiple bit rates. The player client switches between streaming the different encodings depending on available resources.
The streaming client is made aware of the available streams at differing bit rates, and segments of the streams by a manifest file. When starting, the client requests the segments from the lowest bit rate stream. If the client finds the download speed is greater than the bit rate of the segment downloaded, then it will request the next higher bit rate segments.
Later, if the client finds the download speed for a segment is lower than the bit rate for the segment, and therefore the network throughput has deteriorated, then it will request a lower bit rate segment. The segment size can vary depending on the particular implementation, but they are typically between 2 and 10 seconds.
Others use variations of the technology. Netflix and Hulu have used the bit rate scaling for some time to optimize their streaming experience. But Netflix often starts with a lower-bit-rate stream and then slowly scales up, which is why it can take a minute or so before full HD quality sets in.
Buffering, Berkheimer, told GigaOM, is much more noticeable on larger screens. YouTube, he said, is working with the majority of manufacturers in the TV industry to bring adaptive streaming to TV sets. Virtually all new models introduced at CES this year already support the technology. He said the company is also working to bring adaptive streaming to game consoles.
Mobile, on the other hand, comes with different challenges, as people move in and out of the reach of cell towers while they get their video fix on public transport.
“One of the biggest challenges we have is the global nature of YouTube,” said Berkheimer. Average mobile Internet speeds are much slower in India and Brazil than in the U.S. and Europe, but videos still have to play without long and tiresome buffering.
Broadband in Canada on the other hand is fast, but tightly rationed, with major ISPs charging their customers extra if they go over their caps. That’s also one reason, he said, that players have retained manual settings that allow users to manually change the bit rate of a video.