Speex解码的帧与原始帧不同

Question

我需要你的帮助来确定以下定点编码的示例代码(摘自speex手册)中的问题。我测试了对160个样本帧进行编码，然后解码回来，但问题是解码后的帧与原始帧完全不同(参见下面的注释中的输出).What是this?.thanks的可能原因

#include<stdio.h>
#include"intel16.h"
#include <speex/speex.h>
#define FRAME_SIZE 160
#define MAX_NB_BYTES 25

SpeexBits bits;
void *enc_state;
int quality=4;      
int nbBytes;

int byte_ptr;

int frame_size;

short frame[FRAME_SIZE]; 

char outBuffer[20];
SpeexBits decBits;

void *dec_state;

short decFrame[FRAME_SIZE];

int z=0;

int frame_size;

int main (int argc,char **argv)
{
for( z=0;z<160;z++)
    {
    frame[z]=intel_theme[z];  //array of short from "intel16" header file
    }
 printf("\n =================================== \n");

 for( z=0;z<160;z++)
    {
        printf("%i",frame[z]);
    printf ("  ");
        }
     speex_bits_init(&bits);

     enc_state = speex_encoder_init(&speex_nb_mode);



    speex_encoder_ctl(enc_state,SPEEX_GET_FRAME_SIZE,&frame_size);

     speex_encoder_ctl(enc_state,SPEEX_SET_QUALITY,&quality);

     speex_bits_reset(&bits);

      speex_encode_int(enc_state, frame, &bits);     
           // encoding from frame to &bits
     nbBytes = speex_bits_write(&bits, outBuffer, MAX_NB_BYTES); 
         //writing from &bits to outBuffer
//----------------------------------------------------    
     speex_bits_destroy(&bits);

     speex_encoder_destroy(enc_state);  

     printf("\n outBuffer: ");

      for(z=0;z<20;z++)
   {
   printf("%c",outBuffer[z]);
   }
   printf("\n \n");

//-----------DECODING-------------------
speex_bits_init(&decBits);
dec_state=speex_decoder_init(&speex_nb_mode);
speex_decoder_ctl(dec_state, SPEEX_GET_FRAME_SIZE, &frame_size);


speex_bits_read_from(&decBits,outBuffer,nbBytes);
speex_decode_int(dec_state,&decBits,decFrame);
//----------------------------------------------------
printf("\n BUFFER DECODED BACK \n");

for(z=0;z<160;z++)
{
printf("%i",decFrame[z]);
printf ("  ");
}

speex_bits_destroy(&decBits);
speex_decoder_destroy(dec_state);
/*==========END OF DECODING==============*/
printf("\n nbBytes: ");
printf("%i",nbBytes);
printf("\n frame_size= ");
printf("%i",frame_size);
printf ("\n");
//-----------------
printf("end of run!");

return 0;
}

Answer 1

Speex是一种有损编解码器。这意味着解码器的输出通常与编码器的输入略有不同。因为Speex被允许稍微更改数据，所以它可以更多地压缩数据。

http://www.speex.org/docs/manual/speex-manual/node4.html#SECTION00413000000000000000