Use examples when they help make things clearer.

Let me break it down for you! The IA decoder uses a technique called “scalable channel coding” to allow for different levels of spatial resolution in the output signal. This means that instead of encoding all channels at the same bit rate, higher-resolution channels use more bits than lower-resolution ones. When playing back an audio stream with scalable channel coding, the IA decoder chooses which layers of channels to use based on factors like available resources and desired level of spatial detail. For example, if you’re listening in a noisy environment or have limited bandwidth, the decoder might select lower-resolution channels to conserve resources while still providing an immersive audio experience. On the other hand, if you’re in a quiet room with high-quality speakers and plenty of bandwidth, the decoder might choose higher-resolution channels for a more detailed listening experience.

The IA Profiles define a set of capabilities that are required to parse, decode, and process the corresponding IA Sequence. This means that not all codecs can be used in every profile only those that meet certain requirements. For example, the “Low-Latency” profile requires support for real-time processing, while the “High-Quality” profile prioritizes audio fidelity over latency. By defining these profiles, IA ensures compatibility and interoperability between different devices and systems, making it easier to create immersive audio experiences that work across a wide range of platforms.

In terms of handling trimming information in an ISO-BMFF file, the parser passes Descriptors, PTS1 (presentation start time before trimming), IA Samples or Temporal Units, and PTS2 (presentation start time after trimming) to the player. The decoder then processes these samples based on available resources and desired level of spatial detail.

For example, let’s say you have a 7.1.4 channel audio stream that needs to be played back with scalable channel coding. The IA decoder might choose to use only the front left (Ls5) and right (Rs5) channels for lower-resolution playback in a noisy environment, while using all seven channels (Ls7, Rs7, Lc7, Rc7, Llfe, Rlfe, and Blfe) for higher-resolution playback in a quiet room with high-quality speakers. The IA Profiles ensure that the decoder can handle both scenarios seamlessly, while still providing an immersive audio experience.

Overall, scalable channel coding allows for more efficient use of bandwidth while still providing a high-quality immersive audio experience. By defining profiles that meet specific requirements, IA ensures compatibility and interoperability between different devices and systems.