ffmpeg+sdl编程----给ffmpeg加入左右声道切换功能(原创)

这几天忽然相给ffmpeg做的简单播放器加入左右声道切换的功能, 在网上搜索了一下, 居然豪无结果。 网络上有关音轨左右声道切换功能的文章很少, 无论是Google还是百度,很少有相关的收录。有点郁闷，可能是高手们认为太简单不值得一提，新手们有不知所措。求人不如求已， 既然没有人写相关博客，为何不自己尝试一下呢。还好之前有幸看到过来一篇博客有关声道切换filter的代码，它的核心函数是：

HRESULT CAudChlPlace::AudioChannelChg( BYTE *pBuffer, int iSize, int AudioChannel, int AudioBits )
{
int i=0,w_pos=0,r_pos=0, n=0;

n = iSize / 4; //循环次数

switch (AudioBits)
{
case 8:
//进行声道选择
switch(AudioChannel)
{
case 1:r_pos=0;
w_pos=1;
break; //左声道

case 2:r_pos=1;
w_pos=0;
break; //右声道

default:return NOERROR; //不处理（双声道模式）

}
//执行声道切换操作
for(i=0;i<n;i++){
memcpy(pBuffer+w_pos,pBuffer+r_pos,1);
w_pos+=2;
r_pos+=2;
}
break;
case 16:
//进行声道选择
switch(AudioChannel)
{
case 1:r_pos=0;
w_pos=2;
break; //左声道

case 2:r_pos=2;
w_pos=0;
break; //右声道

default:return NOERROR; //不处理（双声道模式）

}
//执行声道切换操作
for(i=0;i<n;i++){
memcpy(pBuffer+w_pos,pBuffer+r_pos,2);
w_pos+=4;
r_pos+=4;
}
break;
case 24:
//进行声道选择
switch(AudioChannel)
{
case 1:r_pos=0;
w_pos=3;
break; //左声道

case 2:r_pos=3;
w_pos=0;
break; //右声道

default:return NOERROR; //不处理（双声道模式）

}
//执行声道切换操作
for(i=0;i<n;i++){
memcpy(pBuffer+w_pos,pBuffer+r_pos,3);
w_pos+=6;
r_pos+=6;
}
break;
case 32:
//进行声道选择
switch(AudioChannel)
{
case 1:r_pos=0;
w_pos=4;
break; //左声道

case 2:r_pos=4;
w_pos=0;
break; //右声道

default:return NOERROR; //不处理（双声道模式）

}
//执行声道切换操作
for(i=0;i<n;i++){
memcpy(pBuffer+w_pos,pBuffer+r_pos,4);
w_pos+=8;
r_pos+=8;
}
break;
}
return S_OK;
}

 所以为将它改写一下用于ffmpeg+sdl的播放器当中，同时在 ffmpeg+sdl教程----编写一个简单的播放器6(其他的时钟同步方式) 基础之前， 对回调函数audio_callback进行改,  同时加入SDL按键处理程序, 实现左箭头-左声首, 右箭头-右声道, 上下箭头-立体声的功能, 具体代码如下:

#include <SDL.h>
#include <SDL_thread.h>

#ifdef main
#undef main /* Prevents SDL from overriding main() */
#endif

#include <stdio.h>
#include <math.h>

#ifdef __cplusplus
extern "C" {
#endif
#include "libavcodec/avcodec.h"
#include "libavformat/avformat.h"
#include "libswscale/swscale.h"
#ifdef __cplusplus
}
#endif

#define SDL_AUDIO_BUFFER_SIZE 1024

#define MAX_AUDIOQ_SIZE (5 * 16 * 1024)
#define MAX_VIDEOQ_SIZE (5 * 256 * 1024)

#define AV_SYNC_THRESHOLD 0.01
#define AV_NOSYNC_THRESHOLD 10.0

#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

typedef struct PacketQueue
{
AVPacketList *first_pkt, *last_pkt;
int nb_packets;
int size;
SDL_mutex *mutex;
SDL_cond *cond;
} PacketQueue;

typedef struct VideoPicture
{
SDL_Overlay *bmp;
int width, height; /* source height & width */
int allocated;
double pts;
} VideoPicture;

typedef struct VideoState
{
AVFormatContext *pFormatCtx;
int videoStream, audioStream;
double audio_clock;
AVStream *audio_st;
PacketQueue audioq;
uint8_t audio_buf[(AVCODEC_MAX_AUDIO_FRAME_SIZE * 3) / 2];
unsigned int audio_buf_size;
unsigned int audio_buf_index;
AVPacket audio_pkt;
uint8_t *audio_pkt_data;
int audio_pkt_size;
int audio_hw_buf_size;
double frame_timer;
double frame_last_pts;
double frame_last_delay;
double video_clock; ///<pts of last decoded frame / predicted pts of next decoded frame
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[1024];
int quit;
} VideoState;

SDL_Surface *screen;

/* Since we only have one decoding thread, the Big Struct
can be global in case we need it. */
VideoState *global_video_state;

int gTrack = 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(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;
}
double get_audio_clock(VideoState *is)
{
double pts;
int hw_buf_size, bytes_per_sec, n;

pts = is->audio_clock; /* maintained in the audio thread */
hw_buf_size = is->audio_buf_size - is->audio_buf_index;
bytes_per_sec = 0;
n = is->audio_st->codec->channels * 2;
if(is->audio_st)
{
bytes_per_sec = is->audio_st->codec->sample_rate * n;
}
if(bytes_per_sec)
{
pts -= (double)hw_buf_size / bytes_per_sec;
}
return pts;
}

int audio_decode_frame(VideoState *is, uint8_t *audio_buf, int buf_size, double *pts_ptr)
{
int len1, data_size, n;
AVPacket *pkt = &is->audio_pkt;
double pts;

for(;;)
{
while(is->audio_pkt_size > 0)
{
data_size = buf_size;
len1 = avcodec_decode_audio2(is->audio_st->codec,
(int16_t *)audio_buf, &data_size,
is->audio_pkt_data, is->audio_pkt_size);
if(len1 < 0)
{
/* if error, skip frame */
is->audio_pkt_size = 0;
break;
}
is->audio_pkt_data += len1;
is->audio_pkt_size -= len1;
if(data_size <= 0)
{
/* No data yet, get more frames */
continue;
}
pts = is->audio_clock;
*pts_ptr = pts;
n = 2 * is->audio_st->codec->channels;
is->audio_clock += (double)data_size /
(double)(n * is->audio_st->codec->sample_rate);

/* 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;
}
/* next packet */
if(packet_queue_get(&is->audioq, pkt, 1) < 0)
{
return -1;
}
is->audio_pkt_data = pkt->data;
is->audio_pkt_size = pkt->size;
/* if update, update the audio clock w/pts */
if(pkt->pts != AV_NOPTS_VALUE)
{
is->audio_clock = av_q2d(is->audio_st->time_base)*pkt->pts;
}
}
}

void audio_track_change(Uint8 *pBuffer, int iSize, int AudioChannel, int AudioBits )
{
int i=0,w_pos=0,r_pos=0, n=0;

n = iSize / 4; //循环次数

switch (AudioBits)
{
case 8:
//进行声道选择
switch(AudioChannel)
{
case 1:r_pos=0;
w_pos=1;
break; //左声道

case 2:r_pos=1;
w_pos=0;
break; //右声道

default:return ; //不处理（双声道模式）

}
//执行声道切换操作
for(i=0;i<n;i++){
memcpy(pBuffer+w_pos,pBuffer+r_pos,1);
w_pos+=2;
r_pos+=2;
}
break;
case 16:
//进行声道选择
switch(AudioChannel)
{
case 1:r_pos=0;
w_pos=2;
break; //左声道

case 2:r_pos=2;
w_pos=0;
break; //右声道

default:return ; //不处理（双声道模式）

}
//执行声道切换操作
for(i=0;i<n;i++){
memcpy(pBuffer+w_pos,pBuffer+r_pos,2);
w_pos+=4;
r_pos+=4;
}
break;
case 24:
//进行声道选择
switch(AudioChannel)
{
case 1:r_pos=0;
w_pos=3;
break; //左声道

case 2:r_pos=3;
w_pos=0;
break; //右声道

default:return; //不处理（双声道模式）

}
//执行声道切换操作
for(i=0;i<n;i++){
memcpy(pBuffer+w_pos,pBuffer+r_pos,3);
w_pos+=6;
r_pos+=6;
}
break;
case 32:
//进行声道选择
switch(AudioChannel)
{
case 1:r_pos=0;
w_pos=4;
break; //左声道

case 2:r_pos=4;
w_pos=0;
break; //右声道

default:return ; //不处理（双声道模式）

}
//执行声道切换操作
for(i=0;i<n;i++){
memcpy(pBuffer+w_pos,pBuffer+r_pos,4);
w_pos+=8;
r_pos+=8;
}
break;
}
return ;
}

void audio_callback(void *userdata, Uint8 *stream, int len)
{
VideoState *is = (VideoState *)userdata;
int len1, audio_size;
double pts;

while(len > 0)
{
if(is->audio_buf_index >= is->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), &pts);
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;
audio_track_change((uint8_t *)is->audio_buf + is->audio_buf_index, len1, gTrack, 16); // 声道控制函数, gTrack 1 - 左声道, 2 - 右声道, 0 - 立体声
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 */
}

/* schedule a video refresh in 'delay' ms */
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)(h * aspect_ratio)) & -3;
if(w > screen->w)
{
w = screen->w;
h = ((int)(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;
double actual_delay, delay, sync_threshold, ref_clock, diff;

if(is->video_st)
{
if(is->pictq_size == 0)
{
schedule_refresh(is, 1);
}
else
{
vp = &is->pictq[is->pictq_rindex];

delay = vp->pts - is->frame_last_pts; /* the pts from last time */
if(delay <= 0 || delay >= 1.0)
{
/* if incorrect delay, use previous one */
delay = is->frame_last_delay;
}
/* save for next time */
is->frame_last_delay = delay;
is->frame_last_pts = vp->pts;

/* update delay to sync to audio */
ref_clock = get_audio_clock(is);
diff = vp->pts - ref_clock;

/* Skip or repeat the frame. Take delay into account
FFPlay still doesn't "know if this is the best guess." */
sync_threshold = (delay > AV_SYNC_THRESHOLD) ? delay : AV_SYNC_THRESHOLD;
if(fabs(diff) < AV_NOSYNC_THRESHOLD)
{
if(diff <= -sync_threshold)
{
delay = 0;
}
else if(diff >= sync_threshold)
{
delay = 2 * delay;
}
}
is->frame_timer += delay;
/* computer the REAL delay */
actual_delay = is->frame_timer - (av_gettime() / 1000000.0);
if(actual_delay < 0.010)
{
/* Really it should skip the picture instead */
actual_delay = 0.010;
}
schedule_refresh(is, (int)(actual_delay * 1000 + 0.5));
/* show the picture! */
video_display(is);

/* update queue for next picture! */
if(++is->pictq_rindex == VIDEO_PICTURE_QUEUE_SIZE)
{
is->pictq_rindex = 0;
}
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, double pts)
{
VideoPicture *vp;
//int dst_pix_fmt;
AVPicture pict;

/* wait until we have space for a new pic */
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;
}
}
/* We have a place to put our picture on the queue */
/* If we are skipping a frame, do we set this to null
but still return vp->allocated = 1? */
static struct SwsContext *img_convert_ctx;
if (img_convert_ctx == NULL)
{
img_convert_ctx = sws_getContext(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_BICUBIC, NULL, NULL, NULL);
if (img_convert_ctx == NULL)
{
fprintf(stderr, "Cannot initialize the conversion context/n");
exit(1);
}
}

if(vp->bmp)
{
SDL_LockYUVOverlay(vp->bmp);

//dst_pix_fmt = PIX_FMT_YUV420P;
/* point pict at the queue */

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];

// Convert the image into YUV format that SDL uses
/*img_convert(&pict, dst_pix_fmt,
(AVPicture *)pFrame, is->video_st->codec->pix_fmt,
is->video_st->codec->width, is->video_st->codec->height);*/
sws_scale(img_convert_ctx, pFrame->data, pFrame->linesize,
0, is->video_st->codec->height, pict.data, pict.linesize);
SDL_UnlockYUVOverlay(vp->bmp);
vp->pts = pts;

/* now we inform our display thread that we have a pic ready */
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;
}

double synchronize_video(VideoState *is, AVFrame *src_frame, double pts)
{
double frame_delay;

if(pts != 0)
{
/* if we have pts, set video clock to it */
is->video_clock = pts;
}
else
{
/* if we aren't given a pts, set it to the clock */
pts = is->video_clock;
}
/* update the video clock */
frame_delay = av_q2d(is->video_st->codec->time_base);
/* if we are repeating a frame, adjust clock accordingly */
frame_delay += src_frame->repeat_pict * (frame_delay * 0.5);
is->video_clock += frame_delay;
return pts;
}
uint64_t global_video_pkt_pts = AV_NOPTS_VALUE;

/* These are called whenever we allocate a frame
* buffer. We use this to store the global_pts in
* a frame at the time it is allocated.
*/
int our_get_buffer(struct AVCodecContext *c, AVFrame *pic)
{
int ret = avcodec_default_get_buffer(c, pic);
uint64_t *pts = (uint64_t *)av_malloc(sizeof(uint64_t));
*pts = global_video_pkt_pts;
pic->opaque = pts;
return ret;
}
void our_release_buffer(struct AVCodecContext *c, AVFrame *pic)
{
if(pic) av_freep(&pic->opaque);
avcodec_default_release_buffer(c, pic);
}

int video_thread(void *arg)
{
VideoState *is = (VideoState *)arg;
AVPacket pkt1, *packet = &pkt1;
int len1, frameFinished;
AVFrame *pFrame;
double pts;

pFrame = avcodec_alloc_frame();

for(;;)
{
if(packet_queue_get(&is->videoq, packet, 1) < 0)
{
// means we quit getting packets
break;
}
pts = 0;

// Save global pts to be stored in pFrame in first call
global_video_pkt_pts = packet->pts;
// Decode video frame
len1 = avcodec_decode_video(is->video_st->codec, pFrame, &frameFinished,
packet->data, packet->size);
if(packet->dts == AV_NOPTS_VALUE
&& pFrame->opaque && *(uint64_t*)pFrame->opaque != AV_NOPTS_VALUE)
{
pts = *(uint64_t *)pFrame->opaque;
}
else if(packet->dts != AV_NOPTS_VALUE)
{
pts = packet->dts;
}
else
{
pts = 0;
}
pts *= av_q2d(is->video_st->time_base);

// Did we get a video frame?
if(frameFinished)
{
pts = synchronize_video(is, pFrame, pts);
if(queue_picture(is, pFrame, pts) < 0)
{
break;
}
}
av_free_packet(packet);
}
av_free(pFrame);
return 0;
}

int stream_component_open(VideoState *is, int stream_index)
{
AVFormatContext *pFormatCtx = is->pFormatCtx;
AVCodecContext *codecCtx;
AVCodec *codec;
SDL_AudioSpec wanted_spec, spec;

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(codecCtx->codec_type == CODEC_TYPE_AUDIO)
{
// Set audio settings from codec info
wanted_spec.freq = codecCtx->sample_rate;
wanted_spec.format = AUDIO_S16SYS;
wanted_spec.channels = codecCtx->channels;
wanted_spec.silence = 0;
wanted_spec.samples = SDL_AUDIO_BUFFER_SIZE;
wanted_spec.callback = audio_callback;
wanted_spec.userdata = is;

if(SDL_OpenAudio(&wanted_spec, &spec) < 0)
{
fprintf(stderr, "SDL_OpenAudio: %s/n", SDL_GetError());
return -1;
}
is->audio_hw_buf_size = spec.size;
}
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];

is->frame_timer = (double)av_gettime() / 1000000.0;
is->frame_last_delay = 40e-3;

packet_queue_init(&is->videoq);
is->video_tid = SDL_CreateThread(video_thread, is);
codecCtx->get_buffer = our_get_buffer;
codecCtx->release_buffer = our_release_buffer;
break;
default:
break;
}
return 0;
}

int decode_interrupt_cb(void)
{
return (global_video_state && global_video_state->quit);
}

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; // Couldn't open file

is->pFormatCtx = pFormatCtx;

// Retrieve stream information
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, is->filename, 0);

// Find the first video stream

for(i=0; i<pFormatCtx->nb_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)
{
stream_component_open(is, audio_index);
}
if(video_index >= 0)
{
stream_component_open(is, video_index);
}

if(is->videoStream < 0 || is->audioStream < 0)
{
fprintf(stderr, "%s: could not open codecs/n", is->filename);
goto fail;
}

// main decode loop

for(;;)
{
if(is->quit)
{
break;
}
// seek stuff goes here
if(is->audioq.size > MAX_AUDIOQ_SIZE ||
is->videoq.size > MAX_VIDEOQ_SIZE)
{
SDL_Delay(10);
continue;
}
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 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:
{
SDL_Event event;
event.type = FF_QUIT_EVENT;
event.user.data1 = is;
SDL_PushEvent(&event);
}
return 0;
}

int main(int argc, char *argv[])
{

SDL_Event event;
VideoState *is;
is = (VideoState *)av_mallocz(sizeof(VideoState));
if(argc < 2)
{
fprintf(stderr, "Usage: test <file>/n");
exit(1);
}
// Register all formats and codecs
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());
exit(1);
}

// Make a screen to put our video
#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);
}

//pstrcpy(is->filename, sizeof(is->filename), argv[1]);
strcpy(is->filename,argv[1]);
is->pictq_mutex = SDL_CreateMutex();
is->pictq_cond = SDL_CreateCond();

schedule_refresh(is, 40);

is->parse_tid = SDL_CreateThread(decode_thread, is);
if(!is->parse_tid)
{
av_free(is);
return -1;
}
for(;;)
{
SDL_WaitEvent(&event);
switch(event.type)
{
case SDL_KEYDOWN:
switch(event.key.keysym.sym)
{
case SDLK_LEFT:
gTrack = 1; // 左声道
break;
case SDLK_RIGHT:
gTrack = 2; // 右声道
break;
case SDLK_UP:
case SDLK_DOWN:
gTrack = 0; // 立体声
break;
default:
break;
}
break;
case FF_QUIT_EVENT:
case SDL_QUIT:
is->quit = 1;
SDL_Quit();
exit(0);
break;
case FF_ALLOC_EVENT:
alloc_picture(event.user.data1);
break;
case FF_REFRESH_EVENT:
video_refresh_timer(event.user.data1);
break;
default:
break;
}
}
return 0;
}

使用方法为: 在控制台输入 tutorial01 den.mpg, 回车播放视频之后, 按左右箭头切换声道.
本程序在win7+vc2008+SDL-1.2.15+FFmpeg-full-SDK-3.2 编译通过.

转自http://blog.163.com/tfn2008@yeah/blog/static/11032131920144314407166/