Data Sheet

PRELIMINARY
VS1063a Datasheet
10 OPERATION
10.7.8 Encoder-Specific Considerations
MP3 (format 5)
The MP3 encoder supports all bitrates and samplerates of the MP3 format, both in mono and
stereo. For details of supported and recommended modes, see Chapter 8.2.1. Notice par-
ticularly that only the MP3 official samplerates are supported (8000, 11025, 12000, 16000,
22050, 24000, 32000, 44100 and 48000 Hz). If you try to start MP3 encoding with any other
samplerate, the encoder will silently fail.
Quality mode, VBR, CBR are the main modes supported by the encoder. If ABR is selected,
VBR mode is used instead. When Quality mode is selected, 5 is designed to be "near PCM
quality" for the given samplerate.
The so-called MP3 bit reservoir offers a way to more efficiently encode MP3 files. To make
streaming more resilient to tranmission errors, encoder only makes bit reservoir references one
frame back.
For some streaming applications it may be beneficial to turn the bit reservoir off by setting bit
10 of register SCI_WRAMADDR before activating encoding. This will make frames more self-
contained. When using ABR/VBR/Quality encoding, turning bit reservoir off will increase the
bitrate approximately 4. . . 16 kbit/s. Turning bit reservoir off in CBR mode is strongly discour-
aged as it will have a huge impact in quality and coding efficiency.
Ogg Vorbis (format 6)
The Ogg Vorbis encoder supports a wide range of bitrates and all samplerates at 8. . . 48 kHz,
in mono and stereo. For some examples of supported modes, see Chapter 8.2.2.
Quality mode is the main mode supported by the encoder. If VBR is selected, the value is
internally converted to a quality value between 0. . . 9, and this value is used. If ABR or CBR
is selected, VBR mode is used instead. When Quality mode is selected, 5 is designed to be
"near PCM quality" for the given samplerate.
When silence is detected, the bitstream width may be reduced by upto 90 %. Because the
encoder attempts to make Ogg frames as long as possible (upto 4 KiB), this means that in
such a case the frame delay may grow dramatically, which may cause problems for streaming
systems. To avoid this, the user may set register SCI_WRAMADDR bit 10 before activating
encoding. This will instruct the encoder to create a frame always after at least 1024 but not
more than 2048 samples have been generated in an Ogg frame.
As a default, the Ogg stream serial number is set to 0xfecaadab. If the user wants to set
a different serial number, he should, prior to activating encoding, write the requested serial
number to (Chapter 10.11) and set bit 11 of register
SCI_WRAMADDR.
Version: 0.42, 2011-11-24 61