下面的代码旨在实现两种策略来插入丢失的数据包 - 这两种策略是 1) 用静音填充间隙,或 2) 重复前一个数据包,如果超过一个数据包,则用静音填充其余数据包。该代码有广泛的评论,但我似乎无法理解不同变量的含义。有人介意帮我理解这段代码吗?感谢任何指导!
#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 < 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 && (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 < 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 < 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;
};