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make gp2x mp3 playback functional (need to unpack and compile helix decoder separately in platform/common/helix)

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kub 2019-03-18 23:14:07 +01:00 • committed by kub
parent c79d0bb90f
commit 340e528ff8
13 changed files with 274 additions and 59 deletions
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27
platform/common/mp3_sync.c Normal file
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@ -0,0 +1,27 @@
int mp3_find_sync_word(const unsigned char *buf, int size)
{
const unsigned char *p, *pe;
/* find byte-aligned syncword - need 12 (MPEG 1,2) or 11 (MPEG 2.5) matching bits */
for (p = buf, pe = buf + size - 3; p <= pe; p++)
{
int pn;
if (p[0] != 0xff)
continue;
pn = p[1];
if ((pn & 0xf8) != 0xf8 || // currently must be MPEG1
(pn & 6) == 0) { // invalid layer
p++; continue;
}
pn = p[2];
if ((pn & 0xf0) < 0x20 || (pn & 0xf0) == 0xf0 || // bitrates
(pn & 0x0c) != 0) { // not 44kHz
continue;
}
return p - buf;
}
return -1;
}