Author: faust3
Date: Sun Jul 26 13:49:32 2009
New Revision: 4807
Log:
clarify some comments
Modified:
wmapro/wmaprodec.c
Modified: wmapro/wmaprodec.c
==============================================================================
--- wmapro/wmaprodec.c Fri Jul 24 12:32:00 2009 (r4806)
+++ wmapro/wmaprodec.c Sun Jul 26 13:49:32 2009 (r4807)
@@ -44,8 +44,20 @@
* subframes. Every subframe contains the data for 2^N time domain samples
* where N varies between 7 and 12.
*
+ * Example wmapro bitstream (in samples):
+ *
+ * || packet 0 || packet 1 || packet 2 packets
+ * ---------------------------------------------------
+ * || frame 0 || frame 1 || frame 2 || frames
+ * ---------------------------------------------------
+ * || | | || | | | || || subframes of channel 0
+ * ---------------------------------------------------
+ * || | | || | | | || || subframes of channel 1
+ * ---------------------------------------------------
+ *
* The frame layouts for the individual channels of a wma frame does not need
* to be the same.
+ *
* However, if the offsets and lengths of several subframes of a frame are the
* same, the subframes of the channels can be grouped.
* Every group may then use special coding techniques like M/S stereo coding
@@ -109,27 +121,27 @@ static VLC coef_vlc[2];
static float sin64[33]; ///< sinus table for decorrelation
/**
- * @brief decoder context for a single channel
+ * @brief frame specific decoder context for a single channel
*/
typedef struct {
int16_t prev_block_len; ///< length of the
previous block
uint8_t transmit_coefs;
uint8_t num_subframes;
uint16_t subframe_len[MAX_SUBFRAMES]; ///< subframe length in
samples
- uint16_t subframe_offset[MAX_SUBFRAMES]; ///< subframe position
- uint8_t cur_subframe; ///< subframe index
- uint16_t channel_len; ///< channel length in
samples
+ uint16_t subframe_offset[MAX_SUBFRAMES]; ///< subframe positions
in the current frame
+ uint8_t cur_subframe; ///< current subframe
number
+ uint16_t channel_len; ///< channel frame
length in samples
uint16_t decoded_samples; ///< already processed
samples
uint8_t grouped; ///< channel is part of
a group
- int quant_step; ///< quantization step
- int8_t transmit_sf; ///< transmit scale
factors
+ int quant_step; ///< quantization step
for the current subframe
+ int8_t transmit_sf; ///< transmit scale
factors for the current subframe
int8_t reuse_sf; ///< share scale factors
between subframes
- int8_t scale_factor_step; ///< scaling step
- int max_scale_factor; ///< maximum scale factor
- int scale_factors[MAX_BANDS]; ///< scale factor values
- int resampled_scale_factors[MAX_BANDS]; ///< scale factors from
a previous block
+ int8_t scale_factor_step; ///< scaling step for
the current subframe
+ int max_scale_factor; ///< maximum scale
factor for the current subframe
+ int scale_factors[MAX_BANDS]; ///< scale factor values
for the current subframe
+ int resampled_scale_factors[MAX_BANDS]; ///< scale factors from
a previous subframe
int16_t scale_factor_block_len; ///< scale factor
reference block length
- float* coeffs; ///< pointer to the
decode buffer
+ float* coeffs; ///< pointer to the
subframe decode buffer
DECLARE_ALIGNED_16(float, out[2*WMAPRO_BLOCK_MAX_SIZE]); ///< output buffer
} WMA3ChannelCtx;
@@ -465,7 +477,7 @@ static av_cold int decode_init(AVCodecCo
* If the subframes are not evenly split, the algorithm estimates the
* channels with the lowest number of total samples.
* Afterwards, for each of these channels a bit is read from the
- * bitstream that indicates if the channel contains a frame with the
+ * bitstream that indicates if the channel contains a subframe with the
* next subframe size that is going to be read from the bitstream or not.
* If a channel contains such a subframe, the subframe size gets added to
* the channel's subframe list.
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