CODEWITHSUNDEEP
htmlvideomobileyoutubestreaming
MSD
MSD

Reputation: 574

How Does YouTube Stream Long-Form Videos to Mobile

I'd like to know how YouTube plays long-form videos so quickly, with seeking, on mobile.

This is an example video: https://www.youtube.com/watch?v=eyU3bRy2x44

I can load it just fine on mobile within 5-15 seconds and I can even seek through it.

Are they using HLS? Or are they using any other streaming technology? Are they using MP4 with highly optimized MOOV Atoms placed at the front of the files?

I'd like to know because I want to serve up long-form videos on one of my websites, and they take forever to load even if served from a CDN.

Thank you in advance!

Upvotes: 0

Views: 254

Answers (2)

Mick
Mick

Reputation: 25491

Your videos should not really take a long time to load even with 'normal' HTTP streaming if the CDN is doing its job properly.

One possible problem might be the quality/bit rate of your videos - if they are only available in high quality or high bit rate then this will definitely cause a delay in initial playback.

Many (most?) YouTube videos now will support multiple bit rates, which allows the client device select the bit rate that is most appropriate for the current network conditions. This technique is called adaptive bit rate streaming, as you likely are aware given the reference to HLS above.

MPEG DASH, as Aquary mentions, is an adaptive bit rate streaming format. It is designed to be an open standard - Apple's HLS, Microsofts's Smooth streaming and Adobe Dynamic Streaming are the other main adaptive bit rate formats.

For videos that support adaptive bit rate streaming the client will usually start up at a low or medium bit rate to ensure quick start up and then 'step up' to the highest bit rate the network will support once the video is playing. This helps fast startup. When you jump to the middle of a video the same approach is used to 'start' again from the point you have selected.

You can quite often see this if you look closely at a video when it starts up - the playback quality will improve after a short while as the video steps up through the bit rates to higher quality streams.

Upvotes: 2

Yury
Yury

Reputation: 691

YouTube uses MPEG-DASH in HTML5 on the devices that are capable of that. This allows seeking through the media and start from the moment which you select.

Traditional progressive download (AKA pseudo-streaming) is not a good option in case of long videos because by default, media players try to download entire video even though you may stop the playback. Seeking is also supported in PD but your video should be prepared for that and your media server needs to be able to process seek requests properly.

Upvotes: 2

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