来源:http://blog.csdn.net/mu399/article/details/5814901
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
[cpp] view plaincopy
- // 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 1024
- static 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;
- }