来自：http://blog.csdn.net/qq_24551315/article/details/51134689
总结网上的G711编解码, 将其一直到andorid系统上去, 通过jni的来进行G711和PCM 的互转, 由于对于这两种格式没有深入的了解,, 所以如果想深入的了解他们可以百度, 在这里只是实现这样的功能罢了.
g711.c 包含编码和解码的方法
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- //http://www.easydarwin.org/article/Streaming/38.html 参考文章
- //https://github.com/EasyDarwin/EasyAACEncoder/blob/master/g711.cpp
- //http://www.oschina.net/code/snippet_1173523_38946
- //http://blog.csdn.net/rightorwrong/article/details/4209467 PCM 2 G711 G711 2 PCM
- unsigned char encode(short pcm);
- short decode(unsigned char alaw);
- /** 个人理解
- * bitsize 应该为16, pBuffer(pcm数据) 两个char 合成一个 short ,长度自然就是原来的一半(nBufferSize/2),
- * 通过编码后short类型的数据变为char类型,让后复制给pCodecBits
- */
- int g711_encode(unsigned char* pCodecBits, const char* pBuffer, int nBufferSize)
- {
- short* buffer = (short*)pBuffer;
- int i;
- for(i=0; i<nBufferSize/2; i++)
- {
- pCodecBits[i] = encode(buffer[i]);
- }
- return nBufferSize/2;
- }
- /** 个人理解
- * bitsize 应该为16, pcm 数组的宽度变为原来两倍(short *out_data = (short*)pRawData;),
- * 通过对pBuffer(g711数据)中char解码转为两个字节的short ,后复制给out_data数组, 在使用的时候又转为char类型, 则 解码后的数据就是原来的两倍(nBufferSize*2)
- */
- int g711_decode(char* pRawData, const unsigned char* pBuffer, int nBufferSize)
- {
- short *out_data = (short*)pRawData;
- int i;
- for(i=0; i<nBufferSize; i++)
- {
- out_data[i] = decode(pBuffer[i]);
- }
- return nBufferSize*2;
- }
- #define MAX 32635
- unsigned char encode(short pcm)
- {
- int sign = (pcm & 0x8000) >> 8;
- if (sign != 0)
- pcm = -pcm;
- if (pcm > MAX) pcm = MAX;
- int exponent = 7;
- int expMask;
- for (expMask = 0x4000; (pcm & expMask) == 0
- && exponent>0; exponent--, expMask >>= 1) { }
- int mantissa = (pcm >> ((exponent == 0) ? 4 : (exponent + 3))) & 0x0f;
- unsigned char alaw = (unsigned char)(sign | exponent << 4 | mantissa);
- return (unsigned char)(alaw^0xD5);
- }
- short decode(unsigned char alaw)
- {
- alaw ^= 0xD5;
- int sign = alaw & 0x80;
- int exponent = (alaw & 0x70) >> 4;
- int data = alaw & 0x0f;
- data <<= 4;
- data += 8;
- if (exponent != 0)
- data += 0x100;
- if (exponent > 1)
- data <<= (exponent - 1);
- return (short)(sign == 0 ? data : -data);
- }
jni中实现编解码,只贴出主要代码
G711 -> PCM
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- JNIEXPORT void JNICALL Java_com_ff_aacdemo_jni_G711Coder_g711Topcm
- (JNIEnv *env, jobject obj){
- FILE* fpOut = fopen("/storage/emulated/0/t/pcm_to_g711.pcm", "wb");
- FILE* fpIn = fopen("/storage/emulated/0/t/pcm_to_g711.g711", "rb");//g711格式文件在最后会给出连接
- int g711_BufferSize = 1024;
- char g711_Buffer[g711_BufferSize];
- int len;
- while((len = fread(g711_Buffer, 1, g711_BufferSize, fpIn)) > 0){
- LOGD("g711topcm length = %d", len);
- char pcmBuffer[len];
- int pcmbufsize = g711_decode(pcmBuffer, g711_Buffer, len);
- fwrite(pcmBuffer, 1, pcmbufsize, fpOut);
- }
- LOGD("g711topcm end");
- fclose(fpIn);
- fclose(fpOut);
- }
PCM -> G711
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- JNIEXPORT void JNICALL Java_com_ff_aacdemo_jni_G711Coder_pcmTog711
- (JNIEnv *env, jobject obj){
- FILE* fpIn = fopen("/storage/emulated/0/t/pcm_to_g711.pcm", "rb");
- FILE* fpOut = fopen("/storage/emulated/0/t/pcm_to_g711.g711", "wb");
- LOGD("pcmTog711 1");
- int pcm_BufferSize = 1024;
- char pcm_Buffer[pcm_BufferSize];
- int len;
- while((len = fread(pcm_Buffer, 1, pcm_BufferSize, fpIn)) > 0){
- LOGD("pcmTog711 length = %d", len);
- char g711Buffer[len];
- int g711BufSize = g711_encode(g711Buffer, pcm_Buffer, len);
- fwrite(g711Buffer, 1, g711BufSize, fpOut);
- }
- LOGD("pcmTog711 end");
- fclose(fpIn);
- fclose(fpOut);
- }
虽然能够实现他们的相互转换, 可是,不怎么好找到播放器播放, 效果始终没有验证, 在下一章中, 将总结将 G711 转换为 AAC , AAC这种格式将能够使用常规的播放器进行播放
g711文件 http://download.csdn.net/detail/yuanzhenhai/2693878
