Advanced Parameters for HTTP-Live-Streaming

HTTP Live Streaming has become a leading standard for multi-screen delivery of video to every device. We've covered this technology in detail in our Definitive Guide to HLS. As the format has gained both broader popularity, and broader device support, the specifications has also evolved. Let's take a closer look at how things have changed, and how Encoding.com has evolved their support for this adaptive bitrate standard.

Apple recently updated the spec for segment size. Previously it had been 10 seconds, but it has now been lowered to 9 seconds. For more information about HLS segmentation, please read Simplify HTTP Live Streaming with the Encoding.com HLS Segmenter'. We've built our own custom segmenter tool that has extremely low overhead creating tremendous storage savings versus other segmenter tools.

Encoding.com now allows you to create multiple h.264 levels for each output. Baseline, Main, and High, can all be mapped based on device parameters. In addition, you can now create audio only HLS streams. We've done this to provide broader and more granular device support. Using Dolby's HE-AAC codec provides much better audio quality at lower bitrates as compared to the open source libfacc codec. This is important since Apple requires a still image with audio fallback for very low bandwidth scenarios. Since different devices support different h.264 profiles and levels, these are now mapped on a device-by-device basis. In addition, Vid.ly, our encode once deliver to all devices OVP, now supports these more granular device parameters, providing more efficient device support. Previously all iOS devices were served a similar h.264 profile and level, and now that will be mapped specifically for each device. We also support the creation of multiple audio streams so the best stream can be delivered on a device by device basis. In addition to audio we also support the latest closed caption standard, WebVTT, ensuring broad accessibility support.

In addition, we now give customers far more granular support over h.264 parameters within HLS. Previously, advanced h.264 parameters within HLS were set to standard defaults. Below are all the advanced h.264 parameters, their definition, and an overview of recommended parameters. This provides broader compatibility for not only iOS devices, but also popular Android devices.

0,1 This parameter should be enabled when encoding high motion video or animation as it improved compression by about 15%. It needs to be enabled when the

parameter is enabled.

0 disabled

1 enabled

0,1,2 This parameter determines rate-distortion, this parameter will generally increase quality and should be enabled.

0 disabled

1 enabled only on the final encode of MB

2 enabled for all mode decisions

0,1,2 bi-directional interpolated prediction frames are a critical component of the h.264 standard, and only supported when using the main and high profiles. Generally this is set to the maximum of 16.

1-9 This parameter determines which algorithm is used for subpixel motion searching and partition decision.

1: High speed, low quality. Only use on first pass encoding.

2-5: A little better, and a little slow processing, 5 serves is good for faster encoding.

6-7: 6 is the most commonly used parameter. Enables rate-distortion optimization for partition decision. Significantly increases efficiency, but there is a measurable speed cost.

8-9: Enables rate-distortion refinement, which refines both motion vectors and intra prediction modes. Slower than 6, but again, more efficient and higher quality.

0-16 An important h.264 feature that allows for reference frames other than the one before or after the current frame. Using this parameter you can specify up to 16 reference frames. For live action 4-6 reference frames will suffice, but for animation 16 should be used. Generally the default is 6.

1, 1b, 1.1, 1.2, 1.3, 2, 2.1, 2.2, 3, 3.1, 3.2, 4, 4.1, 4.2, 5, 5.1 is a specified set of limits that specifies the level of decoder performance. Maximum picture resolution, frame rate, and bit rate that a decoder may use are all specified by the level parameter. WikiPedia has in-depth specs for each parameter.

baseline, main, high This is what the h.264 profile to be used for encoding. There are 21 profiles in total, grouped into baseline, main, and high.

Baseline provides support for intra and inter-coding and entropy encoding with context adaptive variable length codes. (CAVLC) Common use cases for the baseline' profile are VoIP applications. The original iPhone through the 3GS support baseline level 3.0.

Main provides support interlaced video, intercoding using b-slices inter coding using weighted prediction and entropy encoding for context based arithmetic coding (CABC). Common use cases include archival storage of broadcast quality outputs. CABAC entropy coding, b-slices, and interlaced coding are all features unavailable in baseline but available in high. iPhone 4, iPad 1, AppleTV 1 & 2, iPod touch 4 & 5, and newer Android devices support main level 3.1.

High has advanced support for things like quantization scaling matrices and 8 8 transform adaptivity. As you can imagine, the high profile is the profile of choice when encoding HD or broadcast quality content, and is what is used for both Blu-Ray and HDTV services. iPhone 4S+, iPad 2-4, AppleTV 3, newer Android devices support high level 4.1, and some high level 4.2.

It's not just out features that make HLS Pro better. We also provide the ability to package and delivery your HLS content as compressed .zip or .tar files for more efficient delivery. In addition, with up to 16 processing cores encoding times are drastically reduced. In addition we've also rigo

LINK:	http://www.encoding.com/blog/2014/09/03/advanced-parameters-http-live-...
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