A disk-type recording medium such as a Compact Disk (CD) can store high-quality digital audio data permanently, so that it is a popular recording medium. Recently, a Digital Versatile Disk (called ‘DVD’ hereinafter) has been developed as a new disk-type recording medium. A DVD can store much larger size than a CD, such that high-quality moving pictures or audio data are recorded in a DVD for a longer time. Therefore, a DVD will be used widely in the near future.
There are three types in a DVD, DVD-ROM for read-only, DVD-R for write-once, and DVD-RAM or DVD-RW for rewritable. For a rewritable DVD, the standardization of data writing format is in progress.
A disk recording apparatus records an input audio signal to the high-capacity rewritable disk through the following operations. At first, the disk recording apparatus samples at fixed rate an analog audio signal received from an external source. The sampled digital data are encoded into compressed audio data which are converted to EFM binary signals suitable for being written onto the rewritable disk. The converted binary signals are written along a spiral track of the rewritable disk, and the written data are grouped into an ‘Audio Object’ (called ‘AOB hereinafter). The disk recording apparatus creates navigation data for using when searching the written AOB and also writes the navigation data in an appropriate area of the rewritable disk. The navigation data are generated for every creation of an AOB.
An AOB is composed of a plurality of Audio Object Units (called ‘AOBU’s hereinafter). Information regarding the plurality of AOBUs is written in an audio manager information field for the AOB.
Data streams received for a fixed time, for example, 1 second may be grouped into a single AOBU. In case that data streams are received at variable bit rate, the size of each AOBU becomes different from each other if an AOBU groups the written data every 1 second. Therefore, each size information of AOBUs should be written in the audio manager information field allocated for the AOB composed of these AOBUs.
If the input (or writing) bit rate of an audio data stream is very low, the amount of data written during 1 second is much small; however, the received data are grouped into a single AOBU in spite of its small size. Therefore, the number of AOBUs is increased remarkably, which brings about large amount of management information for many AOBUs. The increment of management information reduces a recordable area for real audio data streams.
An AOBU is composed of a plurality of packs whose size is not the exact multiple of an audio frame containing the audio data stream, so that a single audio frame is divided and written in two packs if the remaining area of a pack is smaller than the size of an audio frame. However, an audio frame is not divided at the last pack of an AOBU even though the remaining area of the last pack is insufficient. At this time, the remaining area of the last pack is left unwritten without writing valid data.
Therefore, in case that input data streams are recorded at constant bit rate and data streams received for a fixed time are grouped into a single AOBU, there arise relatively many AOBUs if the input (or writing) bit rate is very low. As a result, the unwritten areas arisen at every last pack of AOBUs are increased remarkably. The increment of unwritten areas reduces a substantial recordable area allocated for real audio data streams.