Method and apparatus for elapsed playback timekeeping of variable bit-rate digitally encoded audio data files
View Patent ↗The present invention involves a digital audio player and a method for processing encoded digital audio data, wherein the digital audio data is encoded using one of a plurality of encoding formats. The audio data player has a hard disk or other data storage medium for storing data files, a microcontroller, buffer memory for anti-skip protection, and an audio decoder. The encoded audio data files and associated decoder files are downloaded from a personal computer or similar device to the audio data player hard drive. The player provides a menu-driven user interface for selection, sorting, and playback of stored audio data files. During playback, elapsed playback time is computed and displayed. For variable bit-rate audio data files, the audio data player generates an elapsed playback timekeeping map concurrently with playback and fast forward scan of audio data files. Concurrently with playback, forward scan, and reverse scan of the audio data file, the audio data player determines the compression ratio for each data portion traversed, and calculates a playback time for each data portion traversed.
1. A method for monitoring in an audio data player, during the processing of an audio data file having data portions capable of having different compression ratios, the elapsed playback for the audio data file, comprising the steps of:
determining the compression ratio and size of each data portion traversed;
calculating the playback time for each data portion traversed based on the compression ratio and size of each data portion traversed; and
displaying the playback time on a display of the audio data player in response to the calculation.
2. The method of claim 1 , wherein the determining step comprises determining elapsed time within the current data portion by interpolation.
3. The method of claim 1 , further including the step of storing the playback time for each data portion traversed in a timekeeping map.
4. The method of claim 1 , further including the step of adjusting an elapsed playback time counter based on the playback time for each data portion traversed.
5. The method of claim 1 , wherein the calculating step comprises calculating elapsed playback time at an input to a buffer feeding an audio data decoder; and the elapsed playback time is adjusted by subtracting an estimated playback time of the data contained in the buffer.
6. The method of claim 1 , wherein the compression ratio is determined based on the bit rate stored in data frame headers of the audio data file; and a confidence estimator locates frame headers and thereby locates the bit rate.
7. The method of claim 1 , wherein the compression ratio is determined based on the bit rate stored in data frame headers of the audio data file; and an interval skipper locates frame headers and thereby locates the bit rate.
8. The method of claim 1 , wherein each data portion includes a fixed time length of audio data and a variable length of data, the length of data being determined by the compression ratio for each data portion.