Limecraft offers extensive support for multi-channel audio, and it allows you to manage different audio channel layouts (or simply "audio layout"). Before you can use audio layouts, they must be properly set up via the production settings. This article explains how to configure the audio layout.
Accessing Audio Layout Settings
To use the audio layout feature, it is required to primarily define the available audio layouts in the production settings, under “Audio Layouts”. Please note production settings are restricted to Account Owners, Account Administrators or Production Administrators. Upon definition, audio layouts defined here can later be applied to clips.
Start by clicking on “Add audio layout”:
On the following screen, start by giving your audio layout a proper name.
Now we will add ‘channel layouts' to indicate the structure of the audio.
Limecraft currently can represent the following types of channel layouts:
Click the ‘Add channel layout’ button and select the type of channel layout you would like to add:
Each channel in the channel layout has to be mapped to the channel in the media containing this information. This requires knowledge of the media you expect in your production.
The example above indicates that the first audio track in the media will contain the Left channel of the first 5.1 channel layout. The second track contains the Center audio and so on.
You can already prefill some metadata fields for the channel layout as well, but this is optional.
Continue adding channel layouts until your audio layout is complete, then press save.
Default audio-layout
You can select one audio-layout as the default. This is the audio layout that will be applied to new media uploaded into your production. You are not obliged to add a default audio layout. However, when also using the ‘multitrack ingest preset’ in your production settings (explained in this article), it is advised to set a default audio layout as the ingest will fail if no audio layout is set.
Note that changing the default audio layout will not affect existing clips in your production.
Advanced mapping
Internally, Limecraft references a clip’s audio channels using the file, track and channel index. A file can contain multiple tracks, and a track may contain multiple channels. The video track is also counted as a track. Indexes are 0-based, which means we start counting at 0 instead of at 1.
As this may be a bit abstract, let’s illustrate this with an example video my-clip, containing stereo audio in French and stereo audio in English. Because we have two stereo mixes in the clip, the total amount of tracks will be 4 (left and right for both French and English). However, the way these 4 channels are stored in the clip can vary a lot. The following lists a few ways of how the clip can be structured in files, tracks and channels. Ignore the last column in the tables for now.
Each channel can have its own audio track:
Or there can be one audio track with 4 channels:
Or there can be two tracks, one with the French audio stereo pair, and one with the English audio stereo pair:
Or for some formats, the audio is stored in separate files:
So, there are three numbers we need to reference a particular channel: the file index, the track index within that file, and the channel index within that track. However, in the previous section, we referenced audio channels using a single number, instead of three. This is done by first sorting all audio channels by file index, then by track index, then by channel index, and then simply number them starting at 1 and counting up. This is illustrated in the last column of the above tables.
The advantage of using a single number to reference the channels is that you don’t need to know exactly how the audio is stored in files, tracks or channels to reference it. You only need to know the order. In some cases, however, you might want to use file, track and channel index to reference your channels. If you know exactly how the audio in your material is structured, you might find it easier to work with file, track and channel numbers.
Click ‘show advanced’ to switch to advanced mapping.
The ‘Track’ inputs are now replaced with ‘Location’ inputs. A location contains three parts, separated by a dot:
the file index (zero-based)
the track index (zero-based)
the channel index, within the track (zero-based)
!! We advise against using the advanced notation unless there is a particular reason to do so.