SECTION 9.2
783
Sounds
TABLE 9.29 Additional entries specific to a sound object
KEY
TYPE
VALUE
Type
name
number
integer
integer
name
(Optional)
The type of PDF object that this dictionary describes; if present, must be
Sound
for a sound object.
(Required)
The sampling rate, in samples per second.
(Optional)
The number of sound channels. Default value: 1. (See implementation
(Optional)
The number of bits per sample value per channel. Default value: 8.
(Optional)
The encoding format for the sample data:
Raw
Unspecified or unsigned values in the range 0 to 2
B
−
1
Signed
Twos-complement values
muLaw
μ-law–encoded
samples
ALaw
A-law–encoded samples
Default value:
Raw
.
R
C
B
E
CO
name
(Optional)
The sound compression format used on the sample data. (This is separate
from any stream compression specified by the sound object’s
Filter
entry; see Table
sion has been used; the data contains sampled waveforms to be played at
R
samples
per second per channel.
(Optional)
Optional parameters specific to the sound compression format used.
Note:
At the time of publication, no standard values have been defined for the
CO
and
CP
entries.
CP
(various)
Sample values are stored in the stream with the most significant bits first (big-en-
dian order for samples larger than 8 bits). Samples that are not a multiple of 8 bits
are packed into consecutive bytes, starting at the most significant end. If a sample
extends across a byte boundary, the most significant bits are placed in the first
byte, followed by less significant bits in subsequent bytes. For dual-channel ste-
reophonic sounds, the samples are stored in an interleaved format, with each
sample value for the left channel (channel 1) preceding the corresponding sample
for the right (channel 2).
To maximize the portability of PDF documents containing embedded sounds, it
is recommended that PDF viewer applications and plug-in extensions support at