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shorten: add some comments

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This commit is contained in:
Justin Ruggles 2011-09-16 17:31:12 -04:00
parent 15d146c958
commit c25762fcf1
1 changed files with 18 additions and 0 deletions
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18
libavcodec/shorten.c
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@ -409,6 +409,7 @@ static int shorten_decode_frame(AVCodecContext *avctx,
int16_t *samples = data;
int ret;
/* allocate internal bitstream buffer */
if(s->max_framesize == 0){
void *tmp_ptr;
s->max_framesize= 1024; // should hopefully be enough for the first header
@ -421,6 +422,7 @@ static int shorten_decode_frame(AVCodecContext *avctx,
s->bitstream = tmp_ptr;
}
/* append current packet data to bitstream buffer */
if(1 && s->max_framesize){//FIXME truncated
buf_size= FFMIN(buf_size, s->max_framesize - s->bitstream_size);
input_buf_size= buf_size;
@ -434,13 +436,17 @@ static int shorten_decode_frame(AVCodecContext *avctx,
buf_size += s->bitstream_size;
s->bitstream_size= buf_size;
/* do not decode until buffer has at least max_framesize bytes */
if(buf_size < s->max_framesize){
*data_size = 0;
return input_buf_size;
}
}
/* init and position bitstream reader */
init_get_bits(&s->gb, buf, buf_size*8);
skip_bits(&s->gb, s->bitindex);
/* process header or next subblock */
if (!s->blocksize)
{
if ((ret = read_header(s)) < 0)
@ -497,6 +503,8 @@ static int shorten_decode_frame(AVCodecContext *avctx,
int residual_size = 0;
int channel = s->cur_chan;
int32_t coffset;
/* get Rice code for residual decoding */
if (cmd != FN_ZERO) {
residual_size = get_ur_golomb_shorten(&s->gb, ENERGYSIZE);
/* this is a hack as version 0 differed in defintion of get_sr_golomb_shorten */
@ -504,6 +512,7 @@ static int shorten_decode_frame(AVCodecContext *avctx,
residual_size--;
}
/* calculate sample offset using means from previous blocks */
if (s->nmean == 0)
coffset = s->offset[channel][0];
else {
@ -514,6 +523,8 @@ static int shorten_decode_frame(AVCodecContext *avctx,
if (s->version >= 2)
coffset >>= FFMIN(1, s->bitshift);
}
/* decode samples for this channel */
if (cmd == FN_ZERO) {
for (i=0; i<s->blocksize; i++)
s->decoded[channel][i] = 0;
@ -521,6 +532,8 @@ static int shorten_decode_frame(AVCodecContext *avctx,
if ((ret = decode_subframe_lpc(s, cmd, channel, residual_size, coffset)) < 0)
return ret;
}
/* update means with info from the current block */
if (s->nmean > 0) {
int32_t sum = (s->version < 2) ? 0 : s->blocksize / 2;
for (i=0; i<s->blocksize; i++)
@ -534,11 +547,16 @@ static int shorten_decode_frame(AVCodecContext *avctx,
else
s->offset[channel][s->nmean - 1] = (sum / s->blocksize) << s->bitshift;
}
/* copy wrap samples for use with next block */
for (i=-s->nwrap; i<0; i++)
s->decoded[channel][i] = s->decoded[channel][i + s->blocksize];
/* shift samples to add in unused zero bits which were removed
during encoding */
fix_bitshift(s, s->decoded[channel]);
/* if this is the last channel in the block, output the samples */
s->cur_chan++;
if (s->cur_chan == s->channels) {
samples = interleave_buffer(samples, s->channels, s->blocksize, s->decoded);