Progressive Download vs. Adaptive Bitrate

How to Choose the Format Right For You

Adaptive bit-rate is an exciting new improvement that optimizing of video quality.  There are three adaptive bit-rate solutions now available from IVA (with a fourth on the way).  However, adaptive bit-rate isn’t the best solution for every situation, so we will continue to make progressive downloads available.  This article reviews the pros and cons of each format so that you can determine which are going to be best suited for your needs.  When you have decided on which format to use, read our Video API for instructions on implementation.

Progressive Download

Progressive downloads in the MP4 format are available to all clients. While progressive downloads lack the heuristic capabilities that optimize quality for screen size and connections, this option offers great flexibility.  We offer speeds that will work on every size device.    This is a good option to choose if you plan on developing for a mobile app and you want the videos to work well on 3g and EDGE networks.   To use this option you either need to generate links to the Video API with fmt=4 or, if you are using the IVA player, set Enable HDS to ‘false’.

Adaptive Bit-rate

Adaptive bit-rate improves the user experience by offering the best video quality available for the screen size and connection being used.  It is particularly beneficial when used in conjunction with large screens or high-resolution devices with lots of available bandwidth.   IVA doesn’t recommend adaptive bit-rate for use with 3G or EDGE Network devices at the present time because of poor performance with the current bit-rates we offer.

There are several versions of adaptive bit-rate streaming in the marketplace and IVA is encoding videos in three of them: HDS, HSS, HLS.  We will soon be encoding in a fourth called DASH.  We are using High Profile for the encodes and are currently offering speeds ranging from 600kbps up to 2500kbps.

Here is a listing of the adaptive bit-rate technologies that IVA is offering:

HDS stands for HTTP Dynamic Streaming and was developed by Adobe.  It delivers adaptive bit-rate standards-based MP4 media over regular HTTP connections.   This format will work only on devices that support Flash.  Check out Adobe’s site for full details.

Microsoft has developed its own adaptive bit-rate format called HTTP Smooth Streaming. It is a part of IIS Media Services and enables streaming media to Silverlight and other clients over HTTP.   HSS detects local bandwidth and CPU conditions to switch bit-rates in near real time to offer the highest quality video that network and device conditions will allow.  The files are delivered in a fragmented MP4 format and are stored as ISMV files.   For more information view Microsoft’s website and download the technical specs and overview.

Apple’s solution to adaptive bit-rate delivery is called HTTP Live Streaming.    The source files for this format are packaged in an MPEG-2 Transport Stream which is then broken up into a series of smaller chunks (.ts files) and referenced in a .M3U8 playlist file index.  Clients read the index file to request the chunks in the correct sequence.  Depending on the available bandwidth the client will choose a chunk from an appropriate bitrate allowing for seamless transitioning between bit-rates.   This format is ideal for streaming video to iOS devices as it is supported natively on iOS 3.0 and later as well as on Safari 4.0 or later.

Supported devices include iPhone 3 and higher, all iPads, Mac OS-X; nearly all set top boxes (Xbox, PS3, Roku, Apple TV, Boxee), as well as Android devices running ICE Cream Sandwich.  IVA will be introducing HLS in a future version of our Flash Player Platform as a plugin which will bring HLS to all PCs supporting Flash.

Dynamic Adaptive Streaming over HTTP is the open source approach to adaptive bit-rate now in development under the auspices of the international MPEG group.  The goal is to have a technology that is universally implemented compared to the more vendor-centric solutions listed above.  The proposed international standard was approved in November 2011.  DASH is audio/video codec agnostic, however the specification provides specific guidance and formats for use with two types of containers, the MPEG-4 file format or the MPEG-2 Transport Stream.  IVA is watching the emerging DASH technology closely and will make encodes available as the standard solidifies.

Adaptive Bitrate Comparison Chart

 Adobe HDSMicrosoft HSSApple HLS3GPP/MPEG DASH
Source Video CodecsH.264, VP6H.264, VC-1H.264H.264 + others(agnostic)
Source Audio CodecsAAC, MP3AAC, WMAAAC, MP3AAC + others(agnostic)
Package/Segment FormatMP4 FragmentsMP4 FragmentsMPEG-2 TSMP4 Fragments + MPEG-2 TS
File storage on serverContiguousContiguousIndividual file per segment (pre iOS 5.0)Contiguous or individual files per segment
Audio/Video/Text packagingMultiplexed in 1 SegmentMultiplexed in 1 segmentMultiplexed in 1 segment( pre iOS 5.0)Multiplexed or separate segments for audio, video
Segmentation & DeliveryAdobe Interactive Server (or Adobe tools + Apache module for on-demandMS IIS (+ few other vendors including Helix)Multiple vendors. Standard HTTP or Streaming servers (+ HelixMultiple vendors. Standard HTTP or Streaming servers (+ Helix)
PlaybackFlash, AirSilverlightApple iOS, Quick Time X3GPP-Rel 9 or MPEG clients
ProtectionFlash AccessPlayReadyAES-128 encryptionFlexible (e.g., OMA or UV)
Typical Segment Duration2-4sec2-4sec10 secFlexible