一个语音通话断续的问题分析
在语音通话过程中，没有规律的卡顿。分析过程包括：
1、网络抓包分析，没有丢包。
2、从MIC进来音频文件，AEC回音消除处理后的wav文件，编码、发送，怀疑回音消除算法影响卡顿。
通过写wav文件对比发现，回音消除算法并没有特别明显的卡顿，但会消掉部分音频。
3、播放端的流程包括，接收RTP，解码，然后扔个ALSA播放。
播放端ALSA声卡偶尔会有underrun的错误，参考表示给声卡喂数据慢了， 导致播放断续。
修改方法：
将音频编码协议从OPUS修改为PCMU，验证播放不卡顿。
问题原因确认：
这个嵌入式linux平台的cpu负载比较高，导致音频播放的解码线程得不到CPU调度，ALSA声卡出现饥饿现象，产生的播放卡顿。
WAV文件读写方法：
下面的读写方法，只用调用两个方法就可以生成一个wav文件。
1、写文件：
inner_file_write_before_encode(采样率，buf，buf_size);
2、录音结束，写文件头
write_header_to_file(文件长度);
代码：
//save 2 file
#include <stdio.h>
#include <ctype.h>
#include <string.h>
#include <stdlib.h>
#include <stdint.h>
#include <errno.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
static int init_file(char *filePath);
static int file_open(const char *filename, int flags);
static int file_read(int fd, unsigned char *buf, int size);
static int file_write(int fd, const unsigned char *buf, int size);
static int64_t file_seek(int fd, int64_t pos, int whence);
static int file_close(int fd);
#define DEBUG_LOCAL_FILE 1
static int g_fd_encode = -1;
static int g_fd_decode = -1;
long total_decoded_data_len = 0;
long total_recorded_data_len = 0;
//static char* save_pcm_before_encoded_file = "/mnt/UDISK/app/aac_before_encoded.wav";
//static char* save_pcm_after_decoded_file = "/mnt/UDISK/app/aac_after_decoded.wav";
static char save_pcm_before_encoded_file[1024] = {0};
static char save_pcm_after_decoded_file[1024] = {0};
static char* tmp_save_pcm_before_encoded_file = "/mnt/UDISK/app/audio/aac_before_encoded";
static char* tmp_save_pcm_after_decoded_file = "/mnt/UDISK/app/audio/aac_after_encoded";
static char* postfix = ".wav";
static char* aacpostfix = ".aac";
#define SAMPLE_RATE_VALUE 16000
static uint8_t get_use_save_for_test(){
return 1;
}
void write_header_to_file(int sample_frame_size){
if (g_fd_decode != -1){
file_close(g_fd_decode);
g_fd_decode = -1;
}
if (g_fd_encode != -1){
file_close(g_fd_encode);
g_fd_encode = -1;
}
int fd_header = file_open(save_pcm_before_encoded_file, O_WRONLY);
if (fd_header != -1){
//int64_t seek = file_seek(fd_header, (int64_t)0, SEEK_END);//SEEK_SET:0 SEEK_CUR:1 SEEK_END:2
//printf("i seek:%d", seek);
//seek = file_seek(fd_header, (int64_t)0, SEEK_SET);//SEEK_SET:0 SEEK_CUR:1 SEEK_END:2
//printf("ii seek:%d", seek);
write_header(fd_header, total_recorded_data_len, total_recorded_data_len + 44, SAMPLE_RATE_VALUE, 1, sample_frame_size);
file_close(fd_header);
}
fd_header = file_open(save_pcm_after_decoded_file, O_WRONLY);
if (fd_header != -1){
//int64_t seek = file_seek(fd_header, (int64_t)0, SEEK_END);//SEEK_SET:0 SEEK_CUR:1 SEEK_END:2
//printf("iii seek:%d", seek);
//seek = file_seek(fd_header, (int64_t)0, SEEK_SET);//SEEK_SET:0 SEEK_CUR:1 SEEK_END:2
// printf("iv seek:%d", seek);
write_header(fd_header, total_decoded_data_len, total_decoded_data_len + 44, SAMPLE_RATE_VALUE, 1, sample_frame_size);
file_close(fd_header);
}
}
typedef unsigned char byte;
/*
8000*1*16/8 channel*samplerate* per_samples_bytes/8
channel:1
samplerate:8000
per_samples_bytes:2*8 16bit pcm
byteRate:160
*/
void write_header(int fd, long totalAudioLen,
long totalDataLen, int longSampleRate, int channels, int byteRate){
unsigned char header[44];
header[0] = 'R'; // RIFF/WAVE header
header[1] = 'I';
header[2] = 'F';
header[3] = 'F';
header[4] = (byte) (totalDataLen & 0xff);
header[5] = (byte) ((totalDataLen >> 8) & 0xff);
header[6] = (byte) ((totalDataLen >> 16) & 0xff);
header[7] = (byte) ((totalDataLen >> 24) & 0xff);
header[8] = 'W';
header[9] = 'A';
header[10] = 'V';
header[11] = 'E';
header[12] = 'f'; // 'fmt ' chunk
header[13] = 'm';
header[14] = 't';
header[15] = ' ';
header[16] = 16; // 4 bytes: size of 'fmt ' chunk
header[17] = 0;
header[18] = 0;
header[19] = 0;
header[20] = 1; // format = 1
header[21] = 0;
header[22] = (byte) channels;
header[23] = 0;
header[24] = (byte) (longSampleRate & 0xff);
header[25] = (byte) ((longSampleRate >> 8) & 0xff);
header[26] = (byte) ((longSampleRate >> 16) & 0xff);
header[27] = (byte) ((longSampleRate >> 24) & 0xff);
header[28] = (byte) (byteRate & 0xff);
header[29] = (byte) ((byteRate >> 8) & 0xff);
header[30] = (byte) ((byteRate >> 16) & 0xff);
header[31] = (byte) ((byteRate >> 24) & 0xff);
header[32] = (byte) (2 * 16 / 8); // block align
header[33] = 0;
header[34] = 16; // bits per sample
header[35] = 0;
header[36] = 'd';
header[37] = 'a';
header[38] = 't';
header[39] = 'a';
header[40] = (byte) (totalAudioLen & 0xff);
header[41] = (byte) ((totalAudioLen >> 8) & 0xff);
header[42] = (byte) ((totalAudioLen >> 16) & 0xff);
header[43] = (byte) ((totalAudioLen >> 24) & 0xff);
file_write(fd, header, 44);
}
int inner_file_write_after_decode(int sample_frame_size, const unsigned char *buf, int size){
if (!get_use_save_for_test()){
//no need do anything.
return -1;
}
static int dcount = 0;
if (g_fd_decode == -1){
//char after_file[1024] = { 0 };
sprintf(save_pcm_after_decoded_file, "%s%d%s", tmp_save_pcm_after_decoded_file, dcount++, aacpostfix);
printf("inner_file_write_after_decode,size:%d save_pcm_after_decoded_file:%s", size, save_pcm_after_decoded_file);
g_fd_decode = init_file(save_pcm_after_decoded_file);
total_decoded_data_len = 0;
write_header(g_fd_decode, total_decoded_data_len, total_decoded_data_len + 44, SAMPLE_RATE_VALUE, 1, sample_frame_size);
return -1;
}
file_write(g_fd_decode, buf, size);
printf("inner_file_write_after_decode,write size:%d", size);
total_decoded_data_len+= size;
}
int inner_file_write_before_encode(int sample_frame_size, const unsigned char *buf, int size){
if (!get_use_save_for_test()){
//no need do anything.
return -1;
}
static int ecount = 0;
if (g_fd_encode == -1){
//char before_file[1024] = { 0 };
sprintf(save_pcm_before_encoded_file, "%s%d%s", tmp_save_pcm_before_encoded_file, ecount++, postfix);
printf("inner_file_write_before_encode, save_pcm_before_encoded_file:%s", save_pcm_before_encoded_file);
g_fd_encode = init_file(save_pcm_before_encoded_file);
total_recorded_data_len = 0;
write_header(g_fd_decode, total_decoded_data_len, total_decoded_data_len + 44, SAMPLE_RATE_VALUE, 1, sample_frame_size);
return -1;
}
file_write(g_fd_encode, buf, size);
total_recorded_data_len+= size;
}
static int init_file(char *filePath){
char* filename = filePath;
remove(filename);
mkdir("/mnt/UDISK/app/", S_IRWXU | S_IRWXG | S_IROTH | S_IXOTH);
mkdir("/mnt/UDISK/app/audio", S_IRWXU | S_IRWXG | S_IROTH | S_IXOTH);
int fd = file_open(filename, O_CREAT | O_WRONLY | O_APPEND);
if (fd == -1){
return -1;
}
return fd ;
}
/**/
static int file_open(const char *filename, int flags)
{
int fd;
fd = open(filename, flags, 0666);
if (fd == -1)
return -1;
return fd;
}
static int file_read(int fd, unsigned char *buf, int size)
{
return read(fd, buf, size);
}
static int file_write(int fd, const unsigned char *buf, int size)
{
return write(fd, buf, size);
}
static int64_t file_seek(int fd, int64_t pos, int whence)
{
return lseek(fd, pos, whence);
}
static int file_close(int fd)
{
return close(fd);
}
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