Flash Player Article

Exploring Flash Player support for high-definition H.264 video and AAC audio

Understanding H.264 and AAC compression

This section provides information on the H.264 video spec guidelines and AAC/AAC+ compression. You will learn what is technically supported in H.264, what standard HD video dimensions are, how H.264 is a container format—and what that means—some basic information on what AAC/AAC+ has to offer, as well as some basic encoding resources.

MPEG-4 H.264

MPEG-4 (Motion Pictures Expert Group) H.264 is an international standard for video compression recognized by the International Organization for Standardization (ISO). H.264 is also known as "MPEG-4 Part 10" or AVC (Advanced Video Coding).

What does that mean? First, it means that when you encode your video for H.264, you're not just encoding it for Flash Player; video can be played back using other software like Apple iTunes or your iPod, or on Sony PlayStation Portable (PSP). With the new hardware scaling and multithreading support of Flash Player, you can now play back video at any resolution and bit rate, including the ultimate high-definition 1080p—as long as the system supports it (see Figure 1).

Figure 1. Screen resolutions and bit rates available with the current video standards

MPEG-4 containers

The MPEG-4 standard also describes a container format, which means that one file can contain several different types of data, stored as tracks. The overall file synchronizes and interleaves the data. So the video or audio in an MPEG-4 container can also be accompanied by metadata, cover art, subtitles, and other textual or visual data that can potentially be extracted by Flash Player. The container can also include multiple video and audio tracks too, but Flash Player will only play back one of each right now and ignores the rest.

AAC/AAC+

Audio files encoded in an MPEG-4 container can now be used in Flash Player if they use the AAC (Advanced Audio Coding) codec. The AAC codec is a lossy compression scheme for audio that has been used since MPEG-2, but has been updated for MPEG-4. It should be familiar to most people, since all music sold from iTunes uses AAC. For you technical folks, it is much higher quality because it can support capture up to 96kHz and can support up to 48 channels and backwards prediction. AAC achieves higher audio quality than MP3 files and maintains similar or lower file sizes. AAC+ or HE-AAC (High Efficiency AAC) is the AAC codec with the addition of parametric stereo and spectral band replication that has been optimized to provide high-quality audio at a low bit rates for applications such as streaming audio. Now you can take advantage of this file format through Flash Player by bringing in MPEG-4 files with AAC encoded audio.

Video encoding

With the H.264 update to Flash Player, video encoding has now been standardized across the entire video ecosystem, including the Adobe Creative Suite 3 family. Tools such as Adobe Premiere and After Effects can now be used to deliver content without using additional plug-ins.

Part of adopting H.264 is leveraging the massive number of solutions on the market. The following is a list of some of the companies that provide industry standard tools for encoding video in the supported format for the new Flash Player 9 Update 3: 

• Anystream
• Digital Rapids
• Kulabyte
• On2 Technologies
• Rhozet
• Sorenson Media
• Telestream
• x264

Supported file formats

Flash Player 9 Update 3 plays files derived from the standard MPEG-4 container format that contain H.264 video and/or HE-AAC audio, such as F4V, MP4, M4A, MOV, MP4V, 3GP, and 3G2. One thing to note is that protected MP4 files, such as those downloaded from iTunes or digitally encrypted by FairPlay, are not supported. For a full list of codecs supported by Flash Player, read the TechNote about it.

To get more information about Flash Player 9 Update 3, visit the Flash Player product page.

To discuss Flash Player 9 Update 3 with the online developer community, visit the main Flash support forums.

Important considerations when streaming H.264 content

One important thing about playing an H.264 video file as progressive download is that the moov atom needs to be located at the beginning of the file, or else the entire file will have to be downloaded before it begins playing. The moov atom is a part of the file that holds index information for the whole file. Unfortunately, tools such as Adobe Premiere and After Effects place this information at the end of the file, but Adobe is working to fix this in a future update to the CS3 video production tools. This isn't an issue for streaming the H.264 video files, however, so Flash Media Server users can breathe easy.

Two open-source solutions to adjusting the moov atom to allow progressive streaming are:

• QTIndexSwapper (Adobe AIR app by Renaun Erickson)
• qt-faststart.c (command-line app by Mike Melanson)

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