在上一篇笔记中我们已经完成了使用SDL播放声音和视频，声音播放没有什么问题，而视频播放太快，很明显视频没有同步。在这里我们要完成视频的同步，同时还要整理程序，使程序的结构更加有条理。
这里先整理以下音频播放的流程：1、从媒体文件中找出音频流的索引（ AudioStream）（遍历AVFormatContext中的streams，通过判断pFormatCtx->streams[i]->codec->codec_type==CODEC_TYPE_AUDIO，找出视频流的索引）；
2、根据音频流索引，找到音频流，再根据音频流，找到音频流的编解码上下文（ AVCodecContext），再通过avcodec_find_decoder函数它找到解码器（AVCodec）；3、通过avcodec_open打开解码器；4、初始化SDL音频设备（设置
音频设备的参数，如音频的采样频率，音频的编码长度等，通过SDL_OpenAudio打开音频设备）；5、为音频包队列分配空间，同时通过SDL_PauseAudio函数真正启动音频设备；6、然后就开始解包媒体文件，把音频包放入音频包队列中，SDL调用回调函数，完成音频的播放（在音频回调函数中，解码音频帧）；
先把代码贴上
#include
#include
#include
#include
#include
#include
#include
//we must customize event
#define FF_ALLOC_EVENT (SDL_USEREVENT)
#define FF_REFRESH_EVENT (SDL_USEREVENT+1)
#define FF_QUIT_EVENT (SDL_USEREVENT+2)
#define VIDEO_PICTURE_QUEUE_SIZE 1
#define SDL_AUDIO_BUFFER_SIZE 1024 //define audio buffer size
#define MAX_AUDIOQ_SIZE (5*16*1024)
#define MAX_VIDEOQ_SIZE (5*256*1024)
//define packet queue
typedef struct PacketQueue {
AVPacketList *first_pkt, *last_pkt;
int nb_packets;
int size;
SDL_mutex *mutex;
SDL_cond *cond;
} PacketQueue;
//define picture queue
typedef struct VideoPicture{
SDL_Overlay *bmp ;
int width ,height ;
int allocated ;//flag that indicate whether bmp is allocated or not
} VideoPicture ;
//for symplifying code ,we stuff all information into one logical unit (a structure )
//VideoState is like a big manager and makes to simplify code
typedef struct VideoState{
AVFormatContext *pFormatCtx ;//media format context
int videoStream,audioStream ;//video stream ID ,audio stream ID
AVStream *audio_st ;//audio stream
PacketQueue audioq ;//audio packet queue
uint8_t audio_buf[((AVCODEC_MAX_AUDIO_FRAME_SIZE*3)/2)] ;//audio buffer
unsigned int audio_buf_size ;
unsigned int audio_buf_index ;
AVPacket audio_pkt ;//audio packet
uint8_t *audio_pkt_data ;
int audio_pkt_size ;
AVStream *video_st ;
PacketQueue videoq ;
VideoPicture pictq[VIDEO_PICTURE_QUEUE_SIZE] ;
int pictq_size,pictq_rindex,pictq_windex ;
SDL_mutex *pictq_mutex ;
SDL_cond *pictq_cond ;
SDL_Thread *parse_tid ;
SDL_Thread *video_tid ;
char filename[256] ;//media filename
int quit ;
} VideoState ;
/* Since we only have one decoding thread, the Big Struct
can be global in case we need it. */
VideoState *global_video_state;
SDL_Surface *screen;
//init packet_queue ;
void packet_queue_init(PacketQueue *q) {
memset(q, 0, sizeof(PacketQueue));//注意这里初始化结构体指针的方法，使用指针一定要先给其分配空间，不用时释放掉
q->mutex = SDL_CreateMutex();
q->cond = SDL_CreateCond();
}
//put audio packet in the queue
int packet_queue_put(PacketQueue *q, AVPacket *pkt) {
AVPacketList *pkt1;
//if pkt is not allocated ,allocate it
if(av_dup_packet(pkt) < 0) {
return -1;
}
//allocate space for new member of queue
pkt1 = av_malloc(sizeof(AVPacketList));
if (!pkt1)
return -1;
//put pkt in pkt1
pkt1->pkt = *pkt;
pkt1->next = NULL;
//lock queue and wait until finishing put
SDL_LockMutex(q->mutex);
//if last_pkt is NULL,it means that the queue is NULL,so put the packet in the first position
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;
//send signal of finish
SDL_CondSignal(q->cond);
SDL_UnlockMutex(q->mutex);
return 0;
}
//put audio packet in the queue
static int packet_queue_get(PacketQueue *q, AVPacket *pkt, int block) {
AVPacketList *pkt1;
int ret;
SDL_LockMutex(q->mutex);
for(;;) {
if(global_video_state->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;
}
//decode audio frame
int audio_decode_frame(VideoState *is, 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(is->audio_st->codec, (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(is->quit) {
return -1;
}
if(packet_queue_get(&is->audioq, &pkt, 1) < 0) {
return -1;
}
audio_pkt_data = pkt.data;
audio_pkt_size = pkt.size;
}
}
//audio callback function
void audio_callback(void *userdata, Uint8 *stream, int len) {
VideoState *is = (VideoState *)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(is, is->audio_buf,
sizeof(is->audio_buf));
if(audio_size < 0) {
/* If error, output silence */
is->audio_buf_size = 1024;
memset(is->audio_buf, 0, is->audio_buf_size);
} else {
is->audio_buf_size = audio_size;
}
is->audio_buf_index = 0;
}
len1 = is->audio_buf_size - is->audio_buf_index;
if(len1 > len)
len1 = len;
memcpy(stream, (uint8_t *)is->audio_buf + is->audio_buf_index, len1);
len -= len1;
stream += len1;
is->audio_buf_index += len1;
}
}
static Uint32 sdl_refresh_timer_cb(Uint32 interval,void *opaque)
{
SDL_Event event ;
event.type = FF_REFRESH_EVENT ;
event.user.data1 = opaque ;
SDL_PushEvent(&event) ;
return 0 ;/* 0 means stop timer*/
}
static void schedule_refresh(VideoState *is ,int delay)
{
SDL_AddTimer(delay,sdl_refresh_timer_cb,is) ;
}
void video_display(VideoState *is)
{
SDL_Rect rect ;
VideoPicture *vp ;
AVPicture pict ;
float aspect_ratio ;
int w,h,x,y ;
int i ;
vp = &is -> pictq[is->pictq_rindex] ;
if(vp->bmp)
{
if(is->video_st->codec->sample_aspect_ratio.num == 0)
{
aspect_ratio = 0 ;
}else
{
aspect_ratio = av_q2d(is->video_st->codec->sample_aspect_ratio)*
is->video_st->codec->width/is->video_st->codec->height ;
}
if(aspect_ratio <= 0.0)
{
aspect_ratio = (float)is->video_st->codec->width/
(float)is ->video_st->codec->height ;
}
h=screen ->h ;
w=((int)rint(h*aspect_ratio)) & -3 ;
if(w >screen->w)
{
w = screen->w ;
h = ((int)rint(w /aspect_ratio)) & -3 ;
}
x = (screen ->w -w )/2 ;
y = (screen ->h -h )/2 ;
rect.x = x ;
rect.y = y ;
rect.w = w ;
rect.h = h ;
SDL_DisplayYUVOverlay(vp->bmp,&rect) ;
}
}
void video_refresh_timer(void *userdata)
{
VideoState *is = (VideoState *)userdata ;
VideoPicture *vp ;
if(is->video_st)
{
if(is->pictq_size == 0)
{
schedule_refresh(is,1) ;
}else
{
vp = &is->pictq[is->pictq_rindex] ;
/* Now, normally here goes a ton of code
about timing, etc. we're just going to
guess at a delay for now. You can
increase and decrease this value and hard code
the timing - but I don't suggest that ;)
We'll learn how to do it for real later.
*/
schedule_refresh(is,10) ;
//show the picture
video_display(is) ;
//update queue for next picture
if(++is->pictq_rindex == VIDEO_PICTURE_QUEUE_SIZE)
{
is->pictq_rindex = 0 ;// notice this is a ring queue
}
SDL_LockMutex(is->pictq_mutex) ;
is->pictq_size-- ;
SDL_CondSignal(is->pictq_cond) ;
SDL_UnlockMutex(is->pictq_mutex) ;
}
}else
{
schedule_refresh(is,100) ;
}
}
void alloc_picture(void *userdata)
{
VideoState *is = (VideoState *)userdata ;
VideoPicture *vp ;
vp = &is->pictq[is->pictq_windex] ;
if(vp->bmp)
{
//we already have one ,make another ,bigger/smaller
SDL_FreeYUVOverlay(vp->bmp) ;
}
//allocate a place to put our YUV image on that screen
vp->bmp = SDL_CreateYUVOverlay(is->video_st->codec->width,
is->video_st->codec->height,
SDL_YV12_OVERLAY,screen) ;
vp->width = is ->video_st->codec->width ;
vp->height = is ->video_st->codec->height ;
SDL_LockMutex(is->pictq_mutex) ;
vp->allocated = 1 ;
SDL_CondSignal(is->pictq_cond) ;
SDL_UnlockMutex(is->pictq_mutex) ;
}
int queue_picture(VideoState *is ,AVFrame *pFrame)
{
VideoPicture *vp ;
//int dst_pix_fmt ;
AVPicture pict ;
struct SwsContext *img_convert_ctx=NULL;
//wait until we have space for a new picture
SDL_LockMutex(is->pictq_mutex) ;
while(is->pictq_size >= VIDEO_PICTURE_QUEUE_SIZE && !is->quit)
{
SDL_CondWait(is->pictq_cond,is->pictq_mutex) ;
}
SDL_UnlockMutex(is->pictq_mutex) ;
if(is->quit)
return -1 ;
//windex is set to 0 initially
vp = &is->pictq[is->pictq_windex] ;
//allocate or resize the buffer !
if(!vp->bmp ||
vp->width != is ->video_st->codec->width ||
vp->height != is->video_st->codec->height)
{
SDL_Event event ;
vp->allocated = 0 ;
//we have to do it in the main thread
event.type = FF_ALLOC_EVENT ;
event.user.data1 = is ;
SDL_PushEvent(&event) ;
//wait until we have a picture allocated
SDL_LockMutex(is->pictq_mutex) ;
while(!vp->allocated && !is->quit)
{
SDL_CondWait(is->pictq_cond,is->pictq_mutex) ;
}
SDL_UnlockMutex(is->pictq_mutex) ;
if(is->quit)
return -1 ;
}
//now we have a place to put out picture on the queue ;
if(vp->bmp)
{
SDL_LockYUVOverlay(vp->bmp) ;
//dst_pix_fmt = PIX_FMT_YUV420P;
pict.data[0]=vp->bmp->pixels[0] ;
pict.data[1]=vp->bmp->pixels[2] ;
pict.data[2]=vp->bmp->pixels[1] ;
pict.linesize[0]=vp->bmp->pitches[0] ;
pict.linesize[1]=vp->bmp->pitches[2] ;
pict.linesize[2]=vp->bmp->pitches[1] ;
img_convert_ctx=sws_getCachedContext(img_convert_ctx,is->video_st->codec->width,
is->video_st->codec->height,is->video_st->codec->pix_fmt,
is->video_st->codec->width,is->video_st->codec->height,PIX_FMT_YUV420P,
SWS_X ,NULL,NULL,NULL) ;
if (img_convert_ctx == NULL)
{
printf("can't init convert context!/n") ;
return -1 ;
}
sws_scale(img_convert_ctx, pFrame->data, pFrame->linesize,
0,is->video_st->codec->width, pict.data, pict.linesize);
SDL_UnlockYUVOverlay(vp->bmp) ;
if(++is->pictq_windex == VIDEO_PICTURE_QUEUE_SIZE)
{
is->pictq_windex = 0 ;
}
SDL_LockMutex(is->pictq_mutex) ;
is->pictq_size++ ;
SDL_UnlockMutex(is->pictq_mutex) ;
}
return 0 ;
}
/**************************************************************
**video decode thread:decode frame from video packet queue and
**put it into picture queue
*************************************************************/
int video_thread(void *arg)
{
VideoState *is = (VideoState *)arg ;
AVPacket pkt1 ,*packet = &pkt1 ;
int len1,frameFinished ;
AVFrame *pFrame ;
pFrame = avcodec_alloc_frame() ;
for(;;)
{
if(packet_queue_get(&is->videoq,packet,1)<0)
{
//means we quit getting packets ;
break ;
}
//decode video frame ;
len1 = avcodec_decode_video(is->video_st->codec,pFrame,&frameFinished,
packet->data,packet->size) ;
//a frame finished ?
if(frameFinished)
{
if(queue_picture(is,pFrame) <0)
break ;
}
av_free_packet(packet) ;
}
av_free(pFrame) ;
return 0 ;
}
/******************************************************************************************
**INPUT :VideoState *is and int stream_index
**FUNCTION :find out codec decoder ,set audio device option ,save information to
**to VideoState (the big structure),launch our video and audio thread.At the same time
**in this function we also insert other options ,such as forcing the codec instead of
** autodetecting
*********************************************************************************************/
int stream_component_open(VideoState *is,int stream_index)
{
AVFormatContext *pFormatCtx = is->pFormatCtx ;
AVCodecContext *codecCtx ;
AVCodec *codec ;
SDL_AudioSpec audio_spec ,spec ;
//make sure input parametre stream_index is correct
if(stream_index<0 || stream_index >= pFormatCtx->nb_streams)
{
return -1 ;
}
//get a pointer to the codec context for the video stream
codecCtx = pFormatCtx->streams[stream_index]->codec ;
//if stream_index identifies a audio stream
if(codecCtx->codec_type == CODEC_TYPE_AUDIO)
{
//set audio device options
audio_spec.freq = codecCtx->sample_rate ;
audio_spec.format = AUDIO_S16SYS;
audio_spec.channels = codecCtx->channels;
audio_spec.silence = 0;
audio_spec.samples = SDL_AUDIO_BUFFER_SIZE;
audio_spec.callback = audio_callback ;
audio_spec.userdata = is ;
//open audio device
if(SDL_OpenAudio(&audio_spec,&spec)<0)
{
fprintf(stderr,"SDL_OpenAudio:%s/n",SDL_GetError()) ;
printf("test4/n") ;
return -1 ;
}
}
codec = avcodec_find_decoder(codecCtx->codec_id) ;
if(!codec || (avcodec_open(codecCtx,codec)<0))
{
fprintf(stderr,"Unsupported codec !/n") ;
return -1 ;
}
switch(codecCtx->codec_type)
{
case CODEC_TYPE_AUDIO:
is -> audioStream = stream_index ;
is -> audio_st = pFormatCtx ->streams[stream_index] ;
is -> audio_buf_size = 0 ;
is -> audio_buf_index = 0 ;
memset(&is->audio_pkt,0,sizeof(is -> audio_pkt)) ;
packet_queue_init(&is ->audioq) ;
SDL_PauseAudio(0) ;
break ;
case CODEC_TYPE_VIDEO:
is ->videoStream = stream_index ;
is ->video_st = pFormatCtx ->streams[stream_index] ;
packet_queue_init(&is->videoq) ;
//create video_thread for reading packet and put it on the right queue ;
is->video_tid = SDL_CreateThread(video_thread,is) ;
break ;
default:
break ;
}
return 0 ;
}
int decode_interrupt_cb(void)
{
return (global_video_state && global_video_state -> quit) ;
}
/*************************************************************
**INPUT : VideoState *is (a big manager manages all the system parameter)
**FUNCTION : init all kind of parametres and read packet from media file and insert it to audio queue or video queue
**
*************************************************************************************/
int decode_thread(void *arg)
{
VideoState *is = (VideoState*)arg ;
AVFormatContext *pFormatCtx ;
AVPacket pkt1,*packet = &pkt1 ;
int video_index = -1 ;
int audio_index = -1 ;
int i ;
is->videoStream = -1 ;
is->audioStream = -1 ;
global_video_state = is ;
//will interrupt blocking functions if we quit !
url_set_interrupt_cb(decode_interrupt_cb) ;
//open video file ;
if(av_open_input_file(&pFormatCtx,is->filename,NULL,0,NULL)!=0)
return -1;
is->pFormatCtx = pFormatCtx ;
//get stream information
if(av_find_stream_info(pFormatCtx)<0)
return -1;
//dump information about file onto standard errror
dump_format(pFormatCtx,0,is->filename,0) ;
//find the first video stream
for(i=0;inb_streams;i++)
{
if(pFormatCtx->streams[i]->codec->codec_type == CODEC_TYPE_VIDEO && video_index<0)
{
video_index = i ;
}
if(pFormatCtx->streams[i]->codec->codec_type == CODEC_TYPE_AUDIO && audio_index<0)
{
audio_index = i ;
}
}
if(audio_index>=0)
{
if(stream_component_open(is,audio_index )== -1)
{
printf("audio stream open failed !/n") ;
}
}
if(video_index>=0)
{
if(stream_component_open(is,video_index ) == -1)
{
printf("video stream open failed!/n") ;
}
}
if(is->videoStream < 0 || is ->audioStream <0)
{
fprintf(stderr,"%s :could not open codecs /n",is->filename) ;
goto fail ;
}
for(;;)
{
if(is->quit)
{
printf("quit/n") ;
break ;
}
//seek stuff goes here
if(is->audioq.size > MAX_AUDIOQ_SIZE ||
is ->videoq.size > MAX_VIDEOQ_SIZE)
{
SDL_Delay(10) ;
continue ;
}
//read packet from file
if(av_read_frame(is ->pFormatCtx,packet) <0)
{
if(url_ferror(&pFormatCtx->pb) == 0)
{
SDL_Delay(100) ;/* no error ; wait for user input */
continue ;
}else
{
break ;
}
}
//is this from a packet from the video stream ?
if(packet->stream_index == is -> videoStream)
{
packet_queue_put(&is->videoq,packet) ;
}else if(packet->stream_index == is -> audioStream)
{
packet_queue_put(&is->audioq,packet) ;
}else
{
av_free_packet(packet) ;
}
}
//all done ,wait for it
while(!is->quit)
{
SDL_Delay(100) ;
}
fail:
if(1)
{
SDL_Event event ;
event.type = FF_QUIT_EVENT ;
event.user.data1 = is ;
SDL_PushEvent(&event) ;
}
return 0 ;
}
int main()
{
SDL_Event event ;
VideoState *is ;
//notice :we must initial two libraries
av_register_all();
if(SDL_Init(SDL_INIT_VIDEO | SDL_INIT_AUDIO | SDL_INIT_TIMER))
{
fprintf(stderr, "Could not initialize SDL - %s/n", SDL_GetError());
return -1 ;
}
#ifndef __DARWIN__
screen = SDL_SetVideoMode(640, 480, 0, 0);
#else
screen = SDL_SetVideoMode(640, 480, 24, 0);
#endif
if(!screen) {
fprintf(stderr, "SDL: could not set video mode - exiting/n");
exit(1);
}
is =av_mallocz(sizeof(VideoState)) ;// allocate space if we define a pointer
//is->filename = "1.asf" ;//media file name ;
//pstrcpy(is->filename, sizeof(is->filename), "1.asf");
av_strlcpy(is->filename,"1.asf",sizeof(is->filename)) ;
//we must create mutex and conditional variable first to avoid race condition
//since we don't know who get information from picture queue first ,decode frame function or display function
is->pictq_mutex = SDL_CreateMutex() ;
is->pictq_cond = SDL_CreateCond() ;
//tell the system to pust a FF_REFRESH_EVENT after the specified number milliseconds
//this will call the video refresh function
schedule_refresh(is,40) ;
//create decode thread ,at the same time we pass 'is' structure as a arguement to the thread
//now we should understand why we define a pointer not a type,we can pass argurement to
//thread convenientely
is->parse_tid = SDL_CreateThread(decode_thread,is) ;
if(!is->parse_tid)
{
av_free(is) ;//remmember free allocated space for videostate
return -1 ;
}
//then the main event loop
while(1)
{
//wait the incidence of event
SDL_WaitEvent(&event) ;
//by the type of envet impliment the corresponding function
switch(event.type)
{
case FF_QUIT_EVENT :
case SDL_QUIT :
is->quit = 1 ;
exit(0) ;
SDL_Quit() ;
return 0 ;
break ;
//allocate a bmp
case FF_ALLOC_EVENT :
alloc_picture(event.user.data1) ;
break ;
//refresh display
case FF_REFRESH_EVENT :
video_refresh_timer(event.user.data1) ;
break ;
default :
break ;
}
}
return 0 ;
}
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