ffmpeg+sdl教程----编写一个简单的播放器3(为视频加入音频)

      上个教程实现了视频的简单播放，但那是个哑巴电影，完全没有声音。

      这个教程第一次用到了SDL的线程，涉及到了两个线程间的同步协调，有几个地方需要特别留意，SDL_OpenAudio库函数会打开音频设备（0是恢复，其他的是暂停），SDL_PauseAudio库函数可以暂停或者恢复audio_callback函数的执行，程序中的这行代码“SDL_PauseAudio(0);”执行后，让audio_callback函数开始反复的被调用。在这之前audio_callback回调函数还没有被调用。

audio_callback函数

     原型为void callback(void *userdata, Uint8 *stream, int len)，userdata是输入，stream是输出，len是输入，len的值一般为4096（调试中发现的），audio_callback函数的功能是调用audio_decode_frame函数，把解码后数据块audio_buf追加在stream的后面，通过SDL库对audio_callback的不断调用，不断解码数据，然后放到stream的末尾，SDL库认为stream中数据够播放一帧音频了，就播放它,第三个参数len是向stream中写数据的内存分配尺度，是分配给audio_callback函数写入缓存大小。

    假设len=4096，解码后数据块audio_buf的大小为4608，那么一次audio_callback调用不能把audio_buf中全部数据写入stream末尾，就分两次，第一次先把audio_buf的前4096个字节写入stream末尾，第二次调用audio_callback函数时，由于写缓存用光了，又分配4096个字节的缓存，再写剩余的512个字节到stream末尾，写缓存还剩余3584个字节留给下次audio_callback调用使用。

audio_decode_frame函数

     原型：int audio_decode_frame(AVCodecContext *aCodecCtx, uint8_t *audio_buf, int buf_size)

     返回值：解码完一帧音频到缓存后，缓存占用的实际大小，以字节为单位，为负数表示失败

     aCodecCtx：输入，解码上下文

     audio_buf：输出，解码成功后，输出到的缓存的首地址

     buf_size：输入，audio_buf的预留空间

     该函数是实际上是从尾部开始执行的，先取得main线程放入队列的包，再用库函数avcodec_decode_audio2处理，如果一次调用没有处理完一个包的数据，记录下处理到包的那个位置了，下次接着处理（这种情况可能是因为一个音频包，包含多个音频帧的数据引起）

库函数avcodec_decode_audio2

    原型:int avcodec_decode_audio2(AVCodecContext *avctx, int16_t *samples,
                         int *frame_size_ptr,
                         const uint8_t *buf, int buf_size);
    avctx ： 解码器上下文
    samples： 输出参数  输出数据的缓存首地址.
    frame_size_ptr：既是输入又是输出，无帧可解返回0，解码失败返回负数，解码成功返回，解码后一帧音频所占空间，以字节为单位
    buf： 输入参数，输入数据的缓存
    buf_size：输入参数，buf的大小
    返回值：无帧可解返回0，解码失败返回负数，解码成功返回解码前一帧音频所占空间

SDL_CondWait库函数

    等待消息时解锁，等到消息后加锁，该函数可以阻塞代码的执行，一般和SDL_CondSignal库函数（或SDL_CondBroadcast库函数）配对使用

 

// ffmpegExe.cpp: 主项目文件。#include "libavformat/avformat.h"#include "libswscale/swscale.h"#include <windows.h>#include <stdlib.h>#include <stdio.h>#include <string.h>#include <math.h>#include <SDL/SDL.h>#include <SDL/SDL_thread.h>#ifdef main#undef main#endif#define SDL_AUDIO_BUFFER_SIZE 1024static int sws_flags = SWS_BICUBIC;typedef struct PacketQueue{ AVPacketList *first_pkt, *last_pkt; int nb_packets; int size; SDL_mutex *mutex; SDL_cond *cond;} PacketQueue;PacketQueue audioq;int quit = 0;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 = (AVPacketList *)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; else q->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;}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); 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){ static AVPacket pkt; static uint8_t *audio_pkt_data = NULL; static int audio_pkt_size = 0; int len1, data_size; for(;;) { while(audio_pkt_size > 0) { data_size = buf_size; len1 = avcodec_decode_audio2(aCodecCtx, (int16_t *)audio_buf, &data_size, audio_pkt_data, audio_pkt_size); if(len1 < 0) { /* if error, skip frame */ audio_pkt_size = 0; break; } audio_pkt_data += len1; audio_pkt_size -= len1; if(data_size <= 0) { /* No data yet, get more frames */ continue; } /* We have data, return it and come back for more later */ return data_size; } if(pkt.data) av_free_packet(&pkt); if(quit) { return -1; } if(packet_queue_get(&audioq, &pkt, 1) < 0) { return -1; } audio_pkt_data = pkt.data; audio_pkt_size = pkt.size; }}void audio_callback(void *userdata, Uint8 *stream, int len){ AVCodecContext *aCodecCtx = (AVCodecContext *)userdata; int len1, audio_size; static uint8_t audio_buf[(AVCODEC_MAX_AUDIO_FRAME_SIZE * 3) / 2]; static unsigned int audio_buf_size = 0; static unsigned int audio_buf_index = 0; while(len > 0) { if(audio_buf_index >= audio_buf_size) { /* We have already sent all our data; get more */ audio_size = audio_decode_frame(aCodecCtx, audio_buf, sizeof(audio_buf)); if(audio_size < 0) { /* If error, output silence */ audio_buf_size = 1024; // arbitrary? memset(audio_buf, 0, audio_buf_size); } else { audio_buf_size = audio_size; } audio_buf_index = 0; } len1 = audio_buf_size - audio_buf_index; if(len1 > len) len1 = len; memcpy(stream, (uint8_t *)audio_buf + audio_buf_index, len1); len -= len1; stream += len1; audio_buf_index += len1; }}int main(int argc, char *argv[]){ AVFormatContext *pFormatCtx; int i, videoStream(-1), audioStream(-1); AVCodecContext *pCodecCtx; AVCodec *pCodec; AVFrame *pFrame; AVPacket packet; int frameFinished; float aspect_ratio; AVCodecContext *aCodecCtx; AVCodec *aCodec; SDL_Overlay *bmp; SDL_Surface *screen; SDL_Rect rect; SDL_Event event; SDL_AudioSpec wanted_spec, spec; if(argc < 2) { fprintf(stderr, "Usage: test /n"); exit(1); } av_register_all(); pFormatCtx = av_alloc_format_context(); if (!pFormatCtx) { fprintf(stderr, "Memory error/n"); exit(1); } if(av_open_input_file(&pFormatCtx, argv[1], NULL, 0, NULL)!=0) return -1; // Couldn't open file if(av_find_stream_info(pFormatCtx)<0) return -1; // Couldn't find stream information // Dump information about file onto standard error dump_format(pFormatCtx, 0, argv[1], 0); // Find the first video stream for(i=0; i<pFormatCtx->nb_streams; i++) { if(pFormatCtx->streams[i]->codec->codec_type==CODEC_TYPE_VIDEO && videoStream<0) { videoStream=i; } if(pFormatCtx->streams[i]->codec->codec_type==CODEC_TYPE_AUDIO && audioStream<0) { audioStream=i; } } if(videoStream==-1||audioStream==-1) return -1; // Didn't find a video stream // Get a pointer to the codec context for the video stream aCodecCtx=pFormatCtx->streams[audioStream]->codec; 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; } aCodec = avcodec_find_decoder(aCodecCtx->codec_id); if(!aCodec) { fprintf(stderr, "Unsupported codec!/n"); return -1; } avcodec_open(aCodecCtx, aCodec); // audio_st = pFormatCtx->streams[index] packet_queue_init(&audioq); SDL_PauseAudio(0); pCodecCtx=pFormatCtx->streams[videoStream]->codec; pCodec=avcodec_find_decoder(pCodecCtx->codec_id); if(pCodec==NULL) { fprintf(stderr, "Unsupported codec!/n"); return -1; // Codec not found } // Open codec if(avcodec_open(pCodecCtx, pCodec)<0) return -1; // Could not open codec // Allocate video frame pFrame=avcodec_alloc_frame(); // Allocate an AVFrame structure uint8_t *buffer; int numBytes; // Determine required buffer size and allocate buffer numBytes=avpicture_get_size(PIX_FMT_RGB24, pCodecCtx->width, pCodecCtx->height); buffer=(uint8_t *)av_malloc(numBytes*sizeof(uint8_t)); // Assign appropriate parts of buffer to image planes in pFrameRGB if(SDL_Init(SDL_INIT_VIDEO | SDL_INIT_AUDIO | SDL_INIT_TIMER)) { fprintf(stderr, "Could not initialize SDL - %s/n", SDL_GetError()); exit(1); }#ifndef __DARWIN__ screen = SDL_SetVideoMode(pCodecCtx->width, pCodecCtx->height, 0, 0);#else screen = SDL_SetVideoMode(pCodecCtx->width, pCodecCtx->height, 24, 0);#endif if(!screen) { fprintf(stderr, "SDL: could not set video mode - exiting/n"); exit(1); } bmp = SDL_CreateYUVOverlay(pCodecCtx->width, pCodecCtx->height, SDL_YV12_OVERLAY, screen); static struct SwsContext *img_convert_ctx; if (img_convert_ctx == NULL) { img_convert_ctx = sws_getContext(pCodecCtx->width, pCodecCtx->height, pCodecCtx->pix_fmt, pCodecCtx->width, pCodecCtx->height, PIX_FMT_YUV420P, sws_flags, NULL, NULL, NULL); if (img_convert_ctx == NULL) { fprintf(stderr, "Cannot initialize the conversion context/n"); exit(1); } } i=0; while(av_read_frame(pFormatCtx, &packet)>=0) { // Is this a packet from the video stream? if(packet.stream_index==videoStream) { // Decode video frame avcodec_decode_video(pCodecCtx, pFrame, &frameFinished, packet.data, packet.size); // Did we get a video frame? if(frameFinished) { SDL_LockYUVOverlay(bmp); AVPicture pict; pict.data[0] = bmp->pixels[0]; pict.data[1] = bmp->pixels[2]; pict.data[2] = bmp->pixels[1]; pict.linesize[0] = bmp->pitches[0]; pict.linesize[1] = bmp->pitches[2]; pict.linesize[2] = bmp->pitches[1]; // Convert the image into YUV format that SDL uses /*img_convert(&pict, PIX_FMT_YUV420P, (AVPicture *)pFrame, pCodecCtx->pix_fmt, pCodecCtx->width, pCodecCtx->height);*/ sws_scale(img_convert_ctx, pFrame->data, pFrame->linesize, 0, pCodecCtx->height, pict.data, pict.linesize); SDL_UnlockYUVOverlay(bmp); rect.x = 0; rect.y = 0; rect.w = pCodecCtx->width; rect.h = pCodecCtx->height; SDL_DisplayYUVOverlay(bmp, &rect); Sleep(60); av_free_packet(&packet); } } else if(packet.stream_index==audioStream) { packet_queue_put(&audioq, &packet); } else { av_free_packet(&packet); } // Free the packet that was allocated by av_read_frame SDL_PollEvent(&event); switch(event.type) { case SDL_QUIT: quit = 1; SDL_Quit(); exit(0); break; default: break; } } // Free the RGB image av_free(buffer); //av_free(pFrameRGB); // Free the YUV frame av_free(pFrame); // Close the codec avcodec_close(pCodecCtx); // Close the video file av_close_input_file(pFormatCtx); return 0;}