Datasheet

VS1053b Datasheet
10 OPERATION
implement perfect fast forward and rewind for WMA and AAC (ADIF, .mp4 / .m4a).
positionMsec is a field that gives the current play position in a file in milliseconds, regardless
of rewind and fast forward operations. The value is only available in codecs that can determine
the play position from the stream itself. Currently WMA and Ogg Vorbis provide this information.
If the position is unknown, this field contains -1.
resync field is used to force a resynchronization to the stream for WMA and AAC (ADIF, .mp4
/ .m4a) instead of ending the decode at first error. This field can be used to implement almost
perfect fast forward and rewind for WMA and AAC (ADIF, .mp4 / .m4a). The user should set this
field before performing data seeks if they are not in packet or data block boundaries. The field
value tells how many tries are allowed before giving up. The value 32767 gives infinite tries.
The resync field is set to 32767 after a reset to make resynchronization the default action, but
it can be cleared after reset to restore the old action. When resync is set, every file decode
should always end as described in Chapter 10.5.1.
Seek fields no longer exist. When resync is required, WMA and AAC codecs now enter broad-
cast/stream mode where file size information is ignored. Also, the file size and sample size in-
formation of WAV files are ignored when resync is non-zero. The user must use SM_CANCEL
or software reset to end decoding.
Note: WAV, WMA, ADIF, and .mp4 / .m4a files begin with a metadata or header section, which
must be fully processed before any fast forward or rewind operation. SS_DO_NOT_JUMP
(in SCI_STATUS) is clear when the header information has been processed and jumps are
allowed.
10.11.2 WMA
Parameter Address Usage
curPacketSize 0x1e2a/2b The size of the packet being processed
packetSize 0x1e2c/2d The packet size in ASF header
The ASF header packet size is available in packetSize. With this information and a packet
start offset from jumpPoints you can parse the packet headers and skip packets in ASF files.
WMA decoder can also increase the internal clock automatically when it detects that a file can
not be decoded correctly with the current clock. The maximum allowed clock is configured with
the SCI_CLOCKF register.
Version: 1.22, 2014-12-19 62