利用ffmpeg１.0提取音频并播放
很久以前，我就想在android做一个复读机程序，用来播放我喜欢的我从网上下的《老友记》，但编一个mp3播放机当然很容易，但其它格式只能借助其它解码工具了，于是在网上找了一堆关于ffmpeg的资料。其它能完成音频播放的工能，欲发几篇文章，一来记录下这几天成果，二是然望能同修们有帮助。
首先的的开发环境是ubuntu,用的是ffmpeg1.0,现在网上很多资料都在很以前比较老的版本，
网上已有很多关于ffmpeg的下载和在lunix底下编译的文章，这里不不多作介绍了，之于利用ndk编译我以后有时间，会说下自己观点和看法。
提取音频程序与解码可能参考 fmpeg-1.0/doc/examples／filtering_audio.c和ffmpeg-1.0/doc/examples/decoding_encoding.c；ffmpeg.c和ffplay太过复杂，对于我这个急于求成的外行来说不太适宜。网上有几篇文章很好比如，
http://ushertechblog.sinaapp.com/post-24.html
#include <stdio.h>#include <libavformat/avformat.h>#include <libswscale/swscale.h>#include <SDL.h>#define SDL_AUDIO_BUFFER_SIZE 1024typedef struct PacketQueue {AVPacketList * first_pkt, *last_pkt;int nb_packets;int size;SDL_mutex *mutex;//mutex主要是用来实现资源的互拆的，跟java里在synchronize关键作用有相似之处//，虽然本和序中没有用多线程，但sdl在播放另启了一个线程。SDL_cond * cond;} PacketQueue;PacketQueue audioq;void packet_queue_init(PacketQueue *q) {memset(q, 0, sizeof(PacketQueue));q->mutex = SDL_CreateMutex();q->cond = SDL_CreateCond();}int packet_queue_put(PacketQueue *q, AVPacket *pkt) {AVPacketList *pkt1;if (av_dup_packet(pkt) < 0)return -1;pkt1 = av_malloc(sizeof(AVPacketList));if (!pkt1)return -1;pkt1->pkt = *pkt;pkt1->next = NULL;SDL_LockMutex(q->mutex);if (!q->last_pkt)q->first_pkt = pkt1;elseq->last_pkt->next = pkt1;q->last_pkt = pkt1;q->nb_packets++;q->size += pkt1->pkt.size;SDL_CondSignal(q->cond);SDL_UnlockMutex(q->mutex);return 0;}int quit = 0;static int packet_queue_get(PacketQueue *q, AVPacket *pkt, int block) {AVPacketList *pkt1;int ret;SDL_LockMutex(q->mutex);for (;;) {if (quit) {ret = -1;break;}pkt1 = q->first_pkt;if (pkt1) {q->first_pkt = pkt1->next;if (!q->first_pkt)q->last_pkt = NULL;q->nb_packets--;q->size -= pkt1->pkt.size;*pkt = pkt1->pkt;av_free(pkt1);//这招我很赞赏，他在取去一个packet后，将上一个paket置空，而在下面的程序就不用再调用av_free操作了ret = 1;break;} else if (!block) {ret = 0;break;} else {SDL_CondWait(q->cond, q->mutex);}}SDL_UnlockMutex(q->mutex);return ret;}//int audio_decode_frame(AVCodecContext *aCodecCtx, uint8_t *audio_buf, int buf_size) {int audio_decode_frame(AVCodecContext *aCodecCtx, AVFrame *frame,uint8_t *audio_buf) {static AVPacket pkt_temp;int len1, data_size, got_frame;int new_packet;for (;;) {while (pkt_temp.size > 0 || (!pkt_temp.data && new_packet)) {if (!frame) {if (!(frame = avcodec_alloc_frame()))return AVERROR(ENOMEM);} else {avcodec_get_frame_defaults(frame);}new_packet = 0;len1 = avcodec_decode_audio4(aCodecCtx, frame, &got_frame,&pkt_temp);if (len1 < 0) {/* if error, skip frame */pkt_temp.size = 0;break;}pkt_temp.data += len1;pkt_temp.size -= len1;if (got_frame <= 0) /* No data yet, get more frames */continue;data_size = av_samples_get_buffer_size(NULL, aCodecCtx->channels,frame->nb_samples, aCodecCtx->sample_fmt, 1);memcpy(audio_buf, frame->data[0], frame->linesize[0]);/* We have data, return it and come back for more later */return data_size;}if (quit)return -1;if ((new_packet = packet_queue_get(&audioq, &pkt_temp, 1)) < 0)return -1;}}void audio_callback(void *userdata, Uint8 *stream, int len) {AVCodecContext *aCodecCtx = (AVCodecContext *) userdata;//以后变量全定义成static ,确保下次循环，变量不会被初始化static uint8_t audio_buf[(AVCODEC_MAX_AUDIO_FRAME_SIZE * 3) / 2];static unsigned int audio_buf_remain_size=0;//记录下audio_buffer剩余数据量static unsigned int audio_buf_total_size=0;//记录下audio_buffer总数据量static unsigned int audio_buf_index = 0;int read_size; //第次送入＊stream中数据的真正长度，理论值是len,但在最后一次操作实际值可能会小于len;AVFrame *frame = NULL;int flag=0;while(len){if(audio_buf_index>=audio_buf_total_size){audio_buf_remain_size = audio_decode_frame(aCodecCtx, frame, audio_buf); audio_buf_total_size=audio_buf_remain_size;audio_buf_index=0;if(audio_buf_total_size<0){audio_buf_remain_size=audio_buf_total_size = 1024;memset(audio_buf, 0, audio_buf_total_size);continue;}}read_size=(audio_buf_remain_size > len)? len : audio_buf_remain_size;memcpy(stream, (uint8_t *) audio_buf + audio_buf_index, read_size);audio_buf_index += read_size;audio_buf_remain_size -= read_size;stream += read_size;len -= read_size;}}int main(int argc, char *argv[]) {AVFormatContext *pFormatCtx;int i, videoStream, audioStream;AVCodecContext *pCodecCtx, *aCodecCtx;AVCodec *pCodec, *aCodec;AVFrame *pFrame;AVFrame *pFrameRGB;AVPacket packet;SDL_Event event;int frameFinished;int numBytes;uint8_t *buffer;if (argc < 2) {printf("Please provide a movie file\n");return -1;}if (SDL_Init(SDL_INIT_AUDIO)) {fprintf(stderr, "Could not initialize SDL - %s\n", SDL_GetError());exit(1);}av_register_all();pFormatCtx = avformat_alloc_context();// Open video file//if(av_open_input_file(&pFormatCtx, argv[1], NULL, 0, NULL)!=0)if (avformat_open_input(&pFormatCtx, argv[1], NULL, NULL ) != 0)return -1; // Couldn't open file// Retrieve stream informationif (avformat_find_stream_info(pFormatCtx, NULL ) < 0)return -1; // Couldn't find stream information// Dump information about file onto standard errorav_dump_format(pFormatCtx, 0, argv[1], 0);// Find the first video streamvideoStream = -1;audioStream = -1;for (i = 0; i < pFormatCtx->nb_streams; i++) {if (pFormatCtx->streams[i]->codec->codec_type == AVMEDIA_TYPE_VIDEO&& videoStream < 0)videoStream = i;if (pFormatCtx->streams[i]->codec->codec_type == AVMEDIA_TYPE_AUDIO&& audioStream < 0)audioStream = i;}if (videoStream == -1)return -1; // Didn't find a video streamif (audioStream == -1)return -1;// Get a pointer to the codec context for the video&audio streampCodecCtx = pFormatCtx->streams[videoStream]->codec;aCodecCtx = pFormatCtx->streams[audioStream]->codec;SDL_AudioSpec wanted_spec, spec;wanted_spec.freq = aCodecCtx->sample_rate;wanted_spec.format = AUDIO_S16SYS;wanted_spec.channels = aCodecCtx->channels;wanted_spec.silence = 0;wanted_spec.samples = SDL_AUDIO_BUFFER_SIZE;wanted_spec.callback = audio_callback;wanted_spec.userdata = aCodecCtx;if (SDL_OpenAudio(&wanted_spec, &spec) < 0) {fprintf(stderr, "SDL_OpenAudio:%s\n", SDL_GetError());return -1;}// Find the decoder for the video streampCodec = avcodec_find_decoder(pCodecCtx->codec_id);if (pCodec == NULL ) {fprintf(stderr, "Unsupported codec!\n");return -1; // Codec not found}// Find the decoder for the video streamaCodec = avcodec_find_decoder(aCodecCtx->codec_id);if (aCodec == NULL ) {fprintf(stderr, "Unsupported codec!\n");return -1; // Codec not found}// Open codecif (avcodec_open2(aCodecCtx, aCodec, NULL ) < 0)return -1; // Could not open codec// Open codecif (avcodec_open2(pCodecCtx, pCodec, NULL ) < 0)return -1; // Could not open codecpacket_queue_init(&audioq);SDL_PauseAudio(0);//Set up a screenwhile (av_read_frame(pFormatCtx, &packet) >= 0) {// Is this a packet from the video stream?if (packet.stream_index == audioStream) {packet_queue_put(&audioq, &packet);} else {av_free_packet(&packet);}SDL_PollEvent(&event);switch (event.type) {case SDL_QUIT:quit = 1;SDL_Quit();exit(0);break;default:break;}}// Free the packet that was allocated by av_read_frameav_free_packet(&packet);// Free the RGB imagefor (;;) {getchar();//这个是用来阻塞主线程，也可以用来接收键盘命令，比如暂停播放之类的break;}// Close the codecavcodec_close(pCodecCtx);avcodec_close(aCodecCtx);// Close the video fileavformat_close_input(&pFormatCtx);return 0;}?