Method and apparatus for converting a compressed audio data stream with fixed frame length including a bit reservoir feature into a different-format data stream

摘要

Data reduction coding/decoding has been standardised e.g. by ISO/IEC standards 11172-3 and 13818-3. "Layer 3" utilises compressed audio data, which are arranged in frames, consisting of consecutive fields of "headers" (2,3,12,13,14) and "audio data" (4,5,6). Typically a mechanism called "bit reservoir" is used, which allows to save some bits in an initial encoding pass. Thereafter the preliminarily saved bits are spent in a further encoding pass for such pieces of the audio signal that require more encoded bits. Using such bit reservoir leads to the fact, that not all data belonging to a single frame are actually contained within that frame. According to the invention, a data stream (1) using the "bit reservoir" feature is converted into a different-format bit stream that uses a different size of the "bit reservoir", for example a smaller size, or a bit reservoir of size zero. The data are rearranged such that less data or no data for a given data frame remain outside that audio frame.