parseAvailabilityBitstream(
		availabilityJson,
		bufferViewsU8,
		lengthBits,
	) {

		if ( ! isNaN( availabilityJson.constant ) ) {

			return {
				constant: Boolean( availabilityJson.constant ),
				lengthBits: lengthBits,
			};

		}
		let bufferView;
		// Check for bitstream first, which is part of the current schema.
		// bufferView is the name of the bitstream from an older schema.
		if ( ! isNaN( availabilityJson.bitstream ) ) {

			bufferView = bufferViewsU8[ availabilityJson.bitstream ];

		} else if ( ! isNaN( availabilityJson.bufferView ) ) {

			bufferView = bufferViewsU8[ availabilityJson.bufferView ];

		}
		return {
			bitstream: bufferView,
			lengthBits: lengthBits
		};

	}
Given the JSON describing an availability bitstream, turn it into an
in-memory representation using an object. This handles bitstreams from a bufferView.

@param {Object} availabilityJson A JSON object representing the availability.
@param {Object} bufferViewsU8 A dictionary of buffer view index to its Uint8Array contents.
@param {number} lengthBits The length of the availability bitstream in bits.
@returns {object}
@private