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POC/C++ - Understanding Audio interpolation code
 

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  1. POC/C++ - Understanding Audio interpolation code
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    <p>The code below is intended to implement two strategies to interpolate across missing packets - the two strategies are 1) fill the gap with silence, or 2) repeat the previous packet and if longer than one packet fill the rest with silence. The code has broad comments but I can't seem to get my head around what the different variables are supposed to mean. Would someone mind giving me a helping hand understanding this code? Appreciate any guidance!</p> <pre><code>#include "interpolate.h" #include "assert.h" /* write a packet's worth of silence */ void write_silence(FILE *ofile, int num_samples) { short missing_pkt[num_samples]; int i; for (i=0; i &lt; num_samples; i++) { missing_pkt[i]=0; } fwrite(missing_pkt, 1, num_samples*2, ofile); } /* simulate the reception of a packet, and apply a loss repair strategy */ void recv_packet(int seqno, int len, char *data, FILE *ofile, int strategy) { static int prev_seqno = -1; static short* prev_samples = 0; /* interpret the data as signed 16 bit integers */ short *samples = (short*)data; int num_samples = len/2; printf("recv_packet: seqno=%d\n", seqno); if (prev_seqno != -1 &amp;&amp; (prev_seqno+1 != seqno)) { int i, missing_seqno; /* there was missing data */ printf("s=%d\n", strategy); switch(strategy) { case SILENCE: { /* create a packet containing silence */ missing_seqno = prev_seqno + 1; while (missing_seqno &lt; seqno) { write_silence(ofile, num_samples); missing_seqno++; } break; } case REPEAT_PREV: { /* repeat the previous packet */ fwrite(prev_samples, 2, num_samples, ofile); missing_seqno = prev_seqno + 2; while (missing_seqno &lt; seqno) { /* repeating the same packet more than once sounds bad */ write_silence(ofile, num_samples); missing_seqno++; } break; } default: abort(); } } fwrite(samples, 1, num_samples*2, ofile); /* hold onto the last received packet - we may need it */ if (prev_samples != 0) free(prev_samples); prev_samples = samples; prev_seqno = seqno; }; </code></pre>
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      1. VTUpMod
    1. COOnce you've figured it out, make sure you add some kind of fade between the good packet and the interpolated one; otherwise, the discontinuity will cause a horrific click.
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      1. USMike Seymour
    2. COtake some time to understand C syntax and basic functions you will need. Seems you are not familiar yet. (ps not C++)
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