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avformat/h261dec: optimize probe 

about 3 times faster

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
This commit is contained in:
Michael Niedermayer 2013-11-09 00:30:27 +01:00
parent c79c7ffc9d
commit 891f33cc70
1 changed files with 17 additions and 20 deletions
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37
libavformat/h261dec.c
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@ -25,33 +25,30 @@
static int h261_probe(AVProbeData *p)
{
uint32_t code= -1;
int i;
int valid_psc=0;
int invalid_psc=0;
int next_gn=0;
int src_fmt=0;
GetBitContext gb;
init_get_bits8(&gb, p->buf, p->buf_size);
for(i=0; i<p->buf_size; i++){
if ((AV_RB16(&p->buf[i]) - 1) < 0xFFU) {
int shift = av_log2_16bit(p->buf[i+1]);
uint32_t code = AV_RB64(&p->buf[FFMAX(i-1, 0)]) >> (24+shift);
if ((code & 0xffff0000) == 0x10000) {
int gn= (code>>12)&0xf;
if(!gn)
src_fmt= code&8;
if(gn != next_gn) invalid_psc++;
else valid_psc++;
for(i=0; i<p->buf_size*8; i++){
if ((code & 0x01ff0000) || !(code & 0xff00)) {
code = (code<<8) + get_bits(&gb, 8);
i += 7;
} else
code = (code<<1) + get_bits1(&gb);
if ((code & 0xffff0000) == 0x10000) {
int gn= (code>>12)&0xf;
if(!gn)
src_fmt= code&8;
if(gn != next_gn) invalid_psc++;
else valid_psc++;
if(src_fmt){ // CIF
next_gn= (gn+1 )%13;
}else{ //QCIF
next_gn= (gn+1+!!gn)% 7;
if(src_fmt){ // CIF
static const int lut[16]={1,2,3,4,5,6,7,8,9,10,11,12,0,1,2,3};
next_gn = lut[gn];
}else{ //QCIF
static const int lut[16]={1,3,4,5,6,0,1,2,3,4,5,6,0,1,2,3,4};
next_gn = lut[gn];
}
}
}
}