Encoding Brief: Phase Out Low Quality Streams in Your Encoding Ladder

Executive Summary: Now might be the time to consider phasing out the lowest quality streams in your encoding ladder to reduce encoding and storage costs. Check your server logs to determine consumption of these streams before doing so. 

Overview and Discussion: All streams in your adaptive group cost money to encode, store, and administrate, even low-quality streams. A recent discussion with an encoding professional at online video platform (OVP) Kaltura indicated that the company's default lowest quality stream for their clients is 640x360@400 kbps (video only). Though clients can request a lower quality streams, like those recommended in TN2224 (below), Kaltura doesn't recommend them out of hand. 

Interestingly, the discussion started after the Kaltura executive, who attended the Streaming Learning Center webinar on Content Aware Encoding, asked webinar host Jan Ozer why he still recommended a 640x360 stream. The executive stated:

Concerning 360p - yep, you are right, it's time to question whether it is relevant. The fact that ladders still have frame sizes lower than 360p, does not really mean that it is actually used in many cases. From my experience there is almost no use for frame sizes lower than 360p. Therefore it is a time to question 360p too.

The Kaltura exec then shared. "Our default encoding set is:

- 400kbps/360p

- 600kbps/360p

- 900kbps/360p

- 1500kbps/720p

- 2500kbps/720p

- 4000/kbps/1080p

There are no renditions ('flavors' in Kaltura terminology) smaller than 360p in the default flavor set, and there are very few customers that ask for smaller flavors. Therefore I know for sure that Kaltura serves very few renditions that are smaller than 360p."

There are many reasons why streams smaller than 360p are not being consumed. Mobile bandwidths have increased to the point where 400 kbps over 3G or 4G is almost assured, and even the smallest mobile device has a screen that's larger than 640x360. For example, the iPhone 4 has a 960x640 resolution screen. Not all videos are useful at very small resolutions with reduced frame rates, so few viewers may decide to access them for playback under these conditions. 

As a counterpoint, however, Netflix recently shared a custom encoding ladder that included a 320x240 stream at 150 kbps. This is the stream on the right in the table below; the stream on the left was from the standard encoding ladder Netflix deployed before instituting per-title encoding parameters. 

The bottom line is that you may be able to reduce encoding and storage costs without stranding any potential viewers. The obvious first step is to check your own server logs to check how many streams in lower than 360p configurations are being consumed.

Recommendations:

1. Identify the streams in your encoding ladder.

2. Check your server logs to identify streams with very low consumption rates. 

3. Consider how many potential viewers eliminating these streams would strand without an alternative, and the potential value of those viewers.

4. If the numbers are low for any streams, particularly at the low end, consider eliminating them from your encoding ladder. 

Additional resources:

How Netflix Pioneered Per-Title Video Encoding Optimization, Streaming Media Magazine, January 14, 2016

Udemy Course: Encoding for Multiple Screen Delivery, www.udemy.com, 18 lessons, 2.5 hours of instruction 

Apple Changes Encoding Recommendations for HLS, Streaming Media Magazine, April 5, 2014

About the Streaming Learning Center:  The Streaming Learning Center is a premiere resource for companies seeking advice or training on cloud or on-premise encoder selection, preset creation, video quality optimization, adaptive bitrate distribution, and associated topics. Please contact Jan Ozer at jan@streaminglearningcenter.com for more information about these services. 


Comments (3)

Said this on 02/23/2016 At 11:34 am

Not sure from which statistics professional people from Kaltura got to say that it's time to remove those lower resolutions ? Residential in big Western cities ?

If I have a look at last 30 days of our worldwide OTT services, there are still 16.5% streams served on lowest bitrate (despite worldwide CDNs) which is 270k, and even 6.5% on 64k audio-only !

So I guess it all depends if you want to keep those users are not, at home, or on the move in a train for example. Financial benefit is really thin for lower bitrates (both storages and bandwidth)

Said this on 02/23/2016 At 12:09 pm
Sylvain:

Good input, thanks for sharing. Definitely want to check your log files before eliminating any streams.

Jan
Anatol Schwarz
Said this on 02/23/2016 At 03:33 pm

The context of the "360p qoute" is whether it is possible to gain qaulity for low bitrate renditions, by increasing the frame size from 360p to 540p. It was not about their removal in order save storage.

The test results that Jan presented in his very interisting webinar, were that in almost all cases the quality measurements for 540p were better than for 360p (for the same bitrate of course). It raises the question whether the low bitrate renditions can use larger frame size like 540p.

Since the current displays are mostly HiRes (720p,1080p,1440p,4k), 360p window will look very small on such displays. Almost too small to see anything. Therefore, the low bitrate renditions probably will be used in full screen mode. In that mode, the 540p would looks better in most cases, then the 360p.

The only reason that I can think of to keep the smaller frame size, is that decode of the 540p will consume more CPU/battery.

Yet again, it is clear that the low bitrate renditions should remain. The question is whether it would be better to increase the frame size of those renditions.

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