ffmpeg--音频的解码和编码

        音频和视频其实是一样的，在文件中寻找音频流，然后解压出来，得到音频帧的数据，同样也可以按照设定的编码格式进行压缩，我这里把音频的解码和编码做成了两个工程，也是直接上代码：

#include <stdio.h>#include <stdlib.h>extern "C"{#include <libavcodec\avcodec.h>#include <libavformat\avformat.h>#include <libswscale\swscale.h>}int main(char arg,char *argv[]){char *filename = argv[1];av_register_all();//注册所有可解码类型AVFormatContext *pInFmtCtx=NULL;//文件格式AVCodecContext *pInCodecCtx=NULL;//编码格式 if (av_open_input_file(&pInFmtCtx, filename, NULL, 0, NULL)!=0)//获取文件格式printf("av_open_input_file error\n");if (av_find_stream_info(pInFmtCtx) < 0)//获取文件内音视频流的信息printf("av_find_stream_info error\n");unsigned int j;// Find the first audio streamint audioStream = -1;for (j=0; j<pInFmtCtx->nb_streams; j++)//找到音频对应的stream{if (pInFmtCtx->streams[j]->codec->codec_type == CODEC_TYPE_AUDIO){audioStream = j;break;}}if (audioStream == -1){printf("input file has no audio stream\n");return 0; // Didn't find a audio stream}printf("audio stream num: %d\n",audioStream);pInCodecCtx = pInFmtCtx->streams[audioStream]->codec; //音频的编码上下文AVCodec *pInCodec = NULL;pInCodec = avcodec_find_decoder(pInCodecCtx->codec_id); //根据编码ID找到用于解码的结构体if (pInCodec == NULL){printf("error no Codec found\n");return -1 ; // Codec not found}if(avcodec_open(pInCodecCtx, pInCodec)<0)//将两者结合以便在下面的解码函数中调用pInCodec中的对应解码函数{printf("error avcodec_open failed.\n");return -1; // Could not open codec}static AVPacket packet;printf(" bit_rate = %d \r\n", pInCodecCtx->bit_rate);printf(" sample_rate = %d \r\n", pInCodecCtx->sample_rate);printf(" channels = %d \r\n", pInCodecCtx->channels);printf(" code_name = %s \r\n", pInCodecCtx->codec->name);printf(" block_align = %d\n",pInCodecCtx->block_align);uint8_t *pktdata;int pktsize;int out_size = AVCODEC_MAX_AUDIO_FRAME_SIZE*100;uint8_t * inbuf = (uint8_t *)malloc(out_size);FILE* pcm;pcm = fopen("result.pcm","wb");long start = clock();while (av_read_frame(pInFmtCtx, &packet) >= 0)//pInFmtCtx中调用对应格式的packet获取函数{if(packet.stream_index==audioStream)//如果是音频{pktdata = packet.data;pktsize = packet.size;while(pktsize>0){out_size = AVCODEC_MAX_AUDIO_FRAME_SIZE*100;//解码int len = avcodec_decode_audio2(pInCodecCtx, (short*)inbuf, &out_size, pktdata, pktsize);if (len < 0){printf("Error while decoding.\n");break;}if(out_size > 0){fwrite(inbuf,1,out_size,pcm);//pcm记录fflush(pcm);}pktsize -= len;pktdata += len;}} av_free_packet(&packet);}long end = clock();printf("cost time :%f\n",double(end-start)/(double)CLOCKS_PER_SEC);free(inbuf);fclose(pcm);if (pInCodecCtx!=NULL){avcodec_close(pInCodecCtx);}av_close_input_file(pInFmtCtx);return 0;}

       文件保存为result.pcm中，现在用这个文件压缩出新的音频文件，代码如下：

void main(){int16_t *samples;uint8_t *audio_outbuf;int audio_outbuf_size;int audio_input_frame_size;double audio_pts;const char* filename = "test.wav";FILE *fin = fopen("result.pcm", "rb"); //音频源文件 AVOutputFormat *fmt;AVFormatContext *oc;AVStream * audio_st;av_register_all();fmt = guess_format(NULL, filename, NULL);oc = av_alloc_format_context();oc->oformat = fmt;snprintf(oc->filename, sizeof(oc->filename), "%s", filename);audio_st = NULL;if (fmt->audio_codec != CODEC_ID_NONE){AVCodecContext *c;audio_st = av_new_stream(oc, 1);c = audio_st->codec;c->codec_id = fmt->audio_codec;c->codec_type = CODEC_TYPE_AUDIO;c->bit_rate = 128000;c->sample_rate = 44100;c->channels = 2;}if (av_set_parameters(oc, NULL) < 0){return;}dump_format(oc, 0, filename, 1);if (audio_st){AVCodecContext* c;AVCodec* codec;c = audio_st->codec;codec = avcodec_find_encoder(c->codec_id);avcodec_open(c, codec);audio_outbuf_size = 10000;audio_outbuf = (uint8_t*)av_malloc(audio_outbuf_size);if (c->frame_size <= 1){audio_input_frame_size = audio_outbuf_size / c->channels;switch (audio_st->codec->codec_id){case CODEC_ID_PCM_S16LE:case CODEC_ID_PCM_S16BE:case CODEC_ID_PCM_U16LE:case CODEC_ID_PCM_U16BE:audio_input_frame_size >>= 1;break;default:break;}}else{audio_input_frame_size = c->frame_size;}samples = (int16_t*)av_malloc(audio_input_frame_size*2*c->channels);}if (!fmt->flags & AVFMT_NOFILE){if (url_fopen(&oc->pb, filename, URL_WRONLY) < 0){return;}}av_write_header(oc);for (;;){if (audio_st){audio_pts = (double)audio_st->pts.val * audio_st->time_base.num / audio_st->time_base.den;}else{audio_pts = 0.0;}if (!audio_st || audio_pts >= 360.0){break;}if (fread(samples, 1, audio_input_frame_size*2*audio_st->codec->channels, fin) <= 0){break;}AVCodecContext* c;AVPacket pkt;av_init_packet(&pkt);c = audio_st->codec;pkt.size = avcodec_encode_audio(c, audio_outbuf, audio_outbuf_size, samples);pkt.pts = av_rescale_q(c->coded_frame->pts, c->time_base, audio_st->time_base);pkt.flags |= PKT_FLAG_KEY;pkt.stream_index = audio_st->index;pkt.data = audio_outbuf;if (av_write_frame(oc, &pkt) != 0){return;}}if (audio_st){avcodec_close(audio_st->codec);av_free(samples);av_free(audio_outbuf);}av_write_trailer(oc);for (int i=0; i<oc->nb_streams; i++){av_freep(&oc->streams[i]->codec);av_freep(&oc->streams[i]);}if (!(fmt->flags & AVFMT_NOFILE)){url_fclose(oc->pb);}av_free(oc);fclose(fin);}