5 \section{Codec Setup and Packet Decode} \label{vorbis:spec:codec}
12 provided in \xref{vorbis:spec:intro}.  \xref{vorbis:spec:bitpacking} covers reading and writing bit fields from
13 and to bitstream packets.
17 \subsection{Header decode and decode setup}
21 and the setup header. All are required for decode compliance.  An
37 is type 1, the comment header type 3 and the setup header type 5
47 to declare the stream definitively as Vorbis, and provide a few externally
64 with this document.  Both \varname{[audio_channels]} and
66 blocksize values are 64, 128, 256, 512, 1024, 2048, 4096 and 8192 in
78   \item Maximum and or minimum set implies a VBR bitstream that obeys the bitrate limits
86 Comment header decode and data specification is covered in
104 configurations, channel mapping configurations and mode
111 \item \varname{[vorbis_codebook_count]} = read eight bits as unsigned integer and add one
127 \item \varname{[vorbis_time_count]} = read 6 bits as unsigned integer and add one
128 \item read \varname{[vorbis_time_count]} 16 bit values; each value should be zero.  If any value is nonzero, this is an error condition and the stream is undecodable.
139  \item \varname{[vorbis_floor_count]} = read 6 bits as unsigned integer and add one
163 \item \varname{[vorbis_residue_count]} = read 6 bits as unsigned integer and add one
188  \item \varname{[vorbis_mapping_count]} = read 6 bits as unsigned integer and add one
197        \item if set, \varname{[vorbis_mapping_submaps]} = read 4 bits as unsigned integer and add one
206              \item \varname{[vorbis_mapping_coupling_steps]} = read 8 bits as unsigned integer and add one
211                  \item the numbers read in the above two steps are channel numbers representing the channel to treat as magnitude and the channel to treat as angle, respectively.  If for any coupling step the angle channel number equals the magnitude channel number, the magnitude channel number is greater than \varname{[audio_channels]}-1, or the angle channel is greater than \varname{[audio_channels]}-1, the stream is undecodable.
229      \item for each submap \varname{[j]} of \varname{[vorbis_mapping_submaps]} submaps, read the floor and residue numbers for use in decoding that submap:
231        \item read and discard 8 bits (the unused time configuration placeholder)
250  \item \varname{[vorbis_mode_count]} = read 6 bits as unsigned integer and add one
259 and \varname{[vorbis_mode_transformtype]}.  \varname{[vorbis_mode_mapping]} must not be greater than the highest number mapping in use.  Any illegal values render the stream undecodable.
264 \item read 1 bit as a framing flag.  If unset, a framing error occurred and the stream is not
277 \subsection{Audio packet decode and synthesis}
280 are audio.  The first step of audio packet decode is to read and
283 must ignore the packet and not attempt decoding it to audio}.
286 \subsubsection{packet type, mode and window decode}
294  \item perform window selection and setup; this window is used later by the inverse MDCT:
322 where $n$ is window size and $x$ ranges $0 \ldots n-1$, but dissimilar
328  \item  if (\varname{[vorbis_mode_blockflag]} is set and \varname{[previous_window_flag]} is
343  \item  if (\varname{[vorbis_mode_blockflag]} is set and \varname{[next_window_flag]} is not
379 \varname{[vorbis_mode_configurations]} and the map number
407 decode zeroing all channel output vectors and skipping to the
416 values (and the floor is zero).  The residue for that vector is not
418 used and some are not, channel coupling could result in mixing a
419 zeroed and nonzeroed vector to produce two nonzeroed vectors.
489  \item for each scalar value \varname{[M]} in vector \varname{[magnitude_vector]} and the corresponding scalar value \varname{[A]} in vector \varname{[angle_vector]}:
537 product of the floor and residue vectors for each channel; the produced
545 fixed-point representation for floor and residue and direct
550 However, floor vector values can span \~140dB (\~24 bits unsigned), and
559 residue vector must be able to represent a 48 bit range and the dot
578 Windowed MDCT output is overlapped and added with the right hand data
582 produced from overlapping the previous and current frame data is
586 one-half block consisting of and only of the overlapped portions. When
587 overlapping a short and long window, much of the returned range does not
611 defined channel locations for 6.1 and 7.1 surround.  Ordering/location
652 	channel use and order is defined by the application
657 mapping as seen fit.  Future channel mappings (such as three and four

Indexes created Thu Feb 14 23:00:39 CET 2013