Preparing audio: considerations
In creating a digital entertainment experience to be streamed to the browser, the upstream considerations are largely the same as for creating assets to be delivered via other delivery routes, such as DVD, OTT streaming services, etc. It’s important to always work, where possible, with the original audio and video files so that when you are ready to do your final mix and encode, the amount of post-production distortion is minimized.
Beyond basic high-quality audio production principles, the main consideration in preparing assets to be optimized for Dolby output is whether you are producing a 2-channel stereo or multichannel (e.g. 5.1, or 7.1/7.2) surround sound experience. If you expect your primary target to be desktop, laptop and mobile devices (and not devices connected to home theater systems), a 2-channel setup has benefits of efficiency and simplicity. Otherwise, if your distribution is likely to be varied you will want to consider a multi-channel mix (that can later be down-mixed).
Mixing and encoding: considerations & tools
Once you’ve collected your content and decided on whether you’re going to produce a multi-channel surround production or a 2-channel stereo one, you’ll begin the process of ingesting your media sources. These could include: raw video footage, audio tracks and sound effects, other video clips, etc. Typically, these will be imported into a non-linear editing system, such as Adobe Premiere, Final Cut Pro, or any of a number of editing systems.
In your editing system, you will need to ensure each sound channel is optimized to play back in the right position at the appropriate levels. For finer-grained control of spatial audio, tools like Adobe Audition and Avid ProTools provide great controls that allow you to vary sound direction and characteristics over time—so, for example, you could have a sound start in the front-left and move rapidly around the room clockwise and then fade out. The sky is the limit using these sophisticated audio processing tools. Rest assured that once you’ve got your final mix playing perfectly in your studio, that the Dolby encoding process will preserve the crucial aspects of your production for perfect playback on any supporting device. Please see this Dolby video for a simple illustration of mixing and encoding a simple short video with audio from multiple sources. For a more extensive demo that uses both Premiere and Audition, see this demo from Adobe. For a more in-depth overview of production principles for preparing a high quality Dolby Audio accompaniment to your video, see the Dolby Made for Web Sound Production Guide.
Encoding audio to Dolby Digital Plus
If you’re already working with Adobe Premiere and Audition, you have a complete Dolby Audio encoding solution in your product. Simply export your video in h.264 for video and then select Dolby|Dolby Digital Plus as the audio encoding codec. Reasonable default parameters are provided and you can adjust these as fits your audio profile. If, on the other hand, your video production files are not mixed in Premiere, you can alternatively use any number of available Dolby Audio encoding solutions. To get started with a small sample file, try out our simple web-based encoder on this site.For larger files, sign up for an encoding.com account and select the video and Dolby Digital Plus parameters you desire.
The most common format you’ll encounter for your video files will be MP4—with an H.264 video track and a Dolby Digital Plus audio track—along with a fallback .mp4 file with an AAC (or other prolific audio codec) track for audio, to play in the event the browser does not yet support Dolby Digital Plus. See the Code section of this site for information on how to detect and play the video file you desire.
For a more robust setup to support high quality assets to a large number of users with varying bandwidth capabilities, you will want to consider delivering you video and audio via a streaming format, such as MPEG-DASH or HLS, both of which support Dolby Digital Plus audio tracks. There are a number of tools which will take your baseline video and audio files and convert them to these formats. Encoding.com provides this as one of the output formats. Other stand-alone tools include both open source and commercial tools, including mp4box, Elemental Stream, and others. Packaging your video and audio tracks in these streaming formats provides a more efficient means to deliver your video over the web. Moreover, they can be configured to play your media in adaptive bitrate, so that depending on the bandwith available to the consumer, the best video/audio tracks will be served, to balance quality with playback capability.