diff options
author | Justin Ruggles <justin.ruggles@gmail.com> | 2011-09-17 01:31:12 +0400 |
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committer | Justin Ruggles <justin.ruggles@gmail.com> | 2011-10-20 21:09:25 +0400 |
commit | c25762fcf1dd61f6b38daf714d72070471e5f76d (patch) | |
tree | 65831b8f7ec9446b8be23e12b465e0d2f88d9352 /libavcodec | |
parent | 15d146c958ec1af1935c2f2b2518f41e0e625d87 (diff) |
shorten: add some comments
Diffstat (limited to 'libavcodec')
-rw-r--r-- | libavcodec/shorten.c | 18 |
1 files changed, 18 insertions, 0 deletions
diff --git a/libavcodec/shorten.c b/libavcodec/shorten.c index f6f920ca7d..a06eb3c497 100644 --- a/libavcodec/shorten.c +++ b/libavcodec/shorten.c @@ -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); |