If you are getting a lot of nasty messages such as “missing frame”, “resending packet” and your sound is cracking sometimes – you’re welcome.
In the previous instruction the not-top version of shairport is fetched.
Go here to get the last version: https://github.com/albertz/shairport.
There were three bugs before (and two of them was fixed in github version). They all are related to hairtunes module.
1) (fixed on github) Function biquad_filt should be
static double biquad_filt(biquad_t *bq, double in) {
double w = in – bq->a[0]*bq->hist[0] – bq->a[1]*bq->hist[1];
double out = bq->b[1]*bq->hist[0] + bq->b[2]*bq->hist[1] + bq->b[0]*w;
bq->hist[1] = bq->hist[0];
bq->hist[0] = w;
return out;
}
instead of
static double biquad_filt(biquad_t *bq, double in) {
double w = in – bq->a[0]*bq->hist[0] – bq->a[1]*bq->hist[1];
double out __attribute__((unused)) = bq->b[1]*bq->hist[0] + bq->b[2]*bq->hist[1] + bq->b[0]*w;
bq->hist[1] = bq->hist[0];
bq->hist[0] = w;
return w;
}
2) (fixed on github) BUFFER_FRAME should be ^2 since sequence number is an unsigned short with overflowing. 512 works pretty well.
3) (not fixed on github) Nice bug in buffer_put_packet function:
Consider the following expression:
if (seqno == ab_write+1)
pretty simple piece of code, but there’s a bug here. Imagine the situation when seqno has overflowed already (eq 0) and ab_write is about to do it (eq 65535). In this case the expression above is NOT true.
ab_write+1 is automatically converted into int and so does seqno. So this expression actually looks like 0==65536, which is FALSE. The fix is quite fast:
if (seqno == (seq_t)(ab_write+1))
That’s all, have fun!