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// tutorial05.c
// A pedagogical video player that really works!
//
// This tutorial was written by Stephen Dranger (dranger@gmail.com).
//
// Code based on FFplay, Copyright (c) 2003 Fabrice Bellard,
// and a tutorial by Martin Bohme (boehme@inb.uni-luebeckREMOVETHIS.de)
// Tested on Gentoo, CVS version 5/01/07 compiled with GCC 4.1.1
//
// Use the Makefile to build all the samples.
//
// Run using
// tutorial05 myvideofile.mpg
//
// to play the video.
#include <libavcodec/avcodec.h>
#include <libavformat/avformat.h>
#include <libavformat/avio.h>
#include <libswresample/swresample.h>
#include <libswscale/swscale.h>
#include <libavutil/avstring.h>
#include <libavutil/opt.h>
#include <libavutil/time.h>
#include <SDL.h>
#include <SDL_thread.h>
#ifdef __MINGW32__
#undef main /* Prevents SDL from overriding main() */
#endif
#include <stdio.h>
#include <math.h>
#define SDL_AUDIO_BUFFER_SIZE 1024
#define MAX_AUDIO_FRAME_SIZE 192000
#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;
// 代表一个视频文件(包括音视频流)
typedef struct VideoState {
AVFormatContext *pFormatCtx; // 流的编解码信息
int videoStream, audioStream; // 音视频流的索引位置
double audio_clock;
AVStream *audio_st; // AVStream存储音视频流的结构体，这里存储音频流
PacketQueue audioq; // 包队列，这里表示音频包队列
AVFrame audio_frame;
uint8_t audio_buf[(MAX_AUDIO_FRAME_SIZE * 3) / 2];
unsigned int audio_buf_size;
unsigned int audio_buf_index;
AVPacket audio_pkt; // AVPacket是存储压缩编码数据相关信息的结构体
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; // AVStream存储音视频流的结构体，这里存储视频流
PacketQueue videoq; // 包队列，这里表示视频包队列
VideoPicture pictq[VIDEO_PICTURE_QUEUE_SIZE]; // 视频缓冲,为了什么
int pictq_size, pictq_rindex, pictq_windex; // 记录读写的位置
SDL_mutex *pictq_mutex;
SDL_cond *pictq_cond;
SDL_Thread *parse_tid;
SDL_Thread *video_tid;
char filename[1024]; // 视频文件名
int quit;
// http://blog.csdn.net/leixiaohua1020/article/details/14215369
AVIOContext *io_context; // AVIOContext是FFMPEG管理输入输出数据的结构体。
struct SwsContext *sws_ctx;
struct SwsContext *sws_ctx_audio;
} 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;
// 初始化队列
void packet_queue_init(PacketQueue *q) {
memset(q, 0, sizeof(PacketQueue));
q->mutex = SDL_CreateMutex();
q->cond = SDL_CreateCond();
}
// 将数据包放置到队列中
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;
else
q->last_pkt->next = pkt1;
q->last_pkt = pkt1;
q->nb_packets++;
q->size += pkt1->pkt.size;
// 然后 SDL_CondSignal()会通过条件变量发送一个信号给接收函数（如果它在等待的话）来告诉它现在已经有数据了，然后解锁互斥量
SDL_CondSignal(q->cond);
SDL_UnlockMutex(q->mutex);
return 0;
}
// 从队列获取数据包
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 decode_frame_from_packet(VideoState *is, AVFrame decoded_frame)
{
int64_t src_ch_layout, dst_ch_layout;
int src_rate, dst_rate;
uint8_t **src_data = NULL, **dst_data = NULL;
int src_nb_channels = 0, dst_nb_channels = 0;
int src_linesize, dst_linesize;
int src_nb_samples, dst_nb_samples, max_dst_nb_samples;
enum AVSampleFormat src_sample_fmt, dst_sample_fmt;
int dst_bufsize;
int ret;
src_nb_samples = decoded_frame.nb_samples;
src_linesize = (int) decoded_frame.linesize;
src_data = decoded_frame.data;
if (decoded_frame.channel_layout == 0) {
decoded_frame.channel_layout = av_get_default_channel_layout(decoded_frame.channels);
}
src_rate = decoded_frame.sample_rate;
dst_rate = decoded_frame.sample_rate;
src_ch_layout = decoded_frame.channel_layout;
dst_ch_layout = decoded_frame.channel_layout;
src_sample_fmt = decoded_frame.format;
dst_sample_fmt = AV_SAMPLE_FMT_S16;
av_opt_set_int(is->sws_ctx_audio, "in_channel_layout", src_ch_layout, 0);
av_opt_set_int(is->sws_ctx_audio, "out_channel_layout", dst_ch_layout, 0);
av_opt_set_int(is->sws_ctx_audio, "in_sample_rate", src_rate, 0);
av_opt_set_int(is->sws_ctx_audio, "out_sample_rate", dst_rate, 0);
av_opt_set_sample_fmt(is->sws_ctx_audio, "in_sample_fmt", src_sample_fmt, 0);
av_opt_set_sample_fmt(is->sws_ctx_audio, "out_sample_fmt", dst_sample_fmt, 0);
/* initialize the resampling context */
if ((ret = swr_init(is->sws_ctx_audio)) < 0) {
fprintf(stderr, "Failed to initialize the resampling context\n");
return -1;
}
/* allocate source and destination samples buffers */
src_nb_channels = av_get_channel_layout_nb_channels(src_ch_layout);
ret = av_samples_alloc_array_and_samples(&src_data, &src_linesize, src_nb_channels, src_nb_samples, src_sample_fmt, 0);
if (ret < 0) {
fprintf(stderr, "Could not allocate source samples\n");
return -1;
}
/* compute the number of converted samples: buffering is avoided
* ensuring that the output buffer will contain at least all the
* converted input samples */
max_dst_nb_samples = dst_nb_samples = av_rescale_rnd(src_nb_samples, dst_rate, src_rate, AV_ROUND_UP);
/* buffer is going to be directly written to a rawaudio file, no alignment */
dst_nb_channels = av_get_channel_layout_nb_channels(dst_ch_layout);
ret = av_samples_alloc_array_and_samples(&dst_data, &dst_linesize, dst_nb_channels, dst_nb_samples, dst_sample_fmt, 0);
if (ret < 0) {
fprintf(stderr, "Could not allocate destination samples\n");
return -1;
}
/* compute destination number of samples */
dst_nb_samples = av_rescale_rnd(swr_get_delay(is->sws_ctx_audio, src_rate) + src_nb_samples, dst_rate, src_rate, AV_ROUND_UP);
/* convert to destination format */
ret = swr_convert(is->sws_ctx_audio, dst_data, dst_nb_samples, (const uint8_t **)decoded_frame.data, src_nb_samples);
if (ret < 0) {
fprintf(stderr, "Error while converting\n");
return -1;
}
dst_bufsize = av_samples_get_buffer_size(&dst_linesize, dst_nb_channels, ret, dst_sample_fmt, 1);
if (dst_bufsize < 0) {
fprintf(stderr, "Could not get sample buffer size\n");
return -1;
}
memcpy(is->audio_buf, dst_data[0], dst_bufsize);
if (src_data) {
av_freep(&src_data[0]);
}
av_freep(&src_data);
if (dst_data) {
av_freep(&dst_data[0]);
}
av_freep(&dst_data);
return dst_bufsize;
}
int audio_decode_frame(VideoState *is, double *pts_ptr) {
int len1, data_size = 0, n;
AVPacket *pkt = &is->audio_pkt;
double pts;
for(;;) {
while(is->audio_pkt_size > 0) {
int got_frame = 0;
len1 = avcodec_decode_audio4(is->audio_st->codec, &is->audio_frame, &got_frame, pkt);
if(len1 < 0) {
/* if error, skip frame */
is->audio_pkt_size = 0;
break;
}
if (got_frame)
{
if (is->audio_frame.format != AV_SAMPLE_FMT_S16) {
data_size = decode_frame_from_packet(is, is->audio_frame);
} else {
data_size =
av_samples_get_buffer_size
(
NULL,
is->audio_st->codec->channels,
is->audio_frame.nb_samples,
is->audio_st->codec->sample_fmt,
1
);
memcpy(is->audio_buf, is->audio_frame.data[0], data_size);
}
}
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_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, &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;
memcpy(stream, (uint8_t *)is->audio_buf + is->audio_buf_index, len1);
len -= len1;
stream += len1;
is->audio_buf_index += len1;
}
}
// 触发事件
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 */
// SDL_AddTimer()是一个 SDL 函数，在一个特定的毫秒数里它简单地回调了用户指定函数（可选择携带一些用户数据）
static void schedule_refresh(VideoState *is, int delay) {
SDL_AddTimer(delay, sdl_refresh_timer_cb, is);
}
// 视频播放的函数
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);
}
}
// 它会从队列里面拉出数据，设置下一帧播放时间，调用 vidoe_display 来使视频显示到屏幕中，队列计数值加 1， 然后减小它的尺寸。
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;
AVPicture pict;
/* wait until we have space for a new pic */
// 队列满的时候，那么等待有空间让我放置
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? */
if(vp->bmp) {
SDL_LockYUVOverlay(vp->bmp);
/* 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
sws_scale
(
is->sws_ctx,
(uint8_t const * const *)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 = 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 frameFinished;
AVFrame *pFrame;
double pts;
pFrame = av_frame_alloc();
for(;;) {
// 从队列里面获取数据出错就退出
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
avcodec_decode_video2(is->video_st->codec, pFrame, &frameFinished,
packet);
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;
}
// stream_component_open()函数的作用是找到解码器，设置音频参数，保存重要信息到大结构体中，然后启动音频和视频线程。
int stream_component_open(VideoState *is, int stream_index) {
AVFormatContext *pFormatCtx = is->pFormatCtx;
AVCodecContext *codecCtx = NULL;
AVCodec *codec = NULL;
AVDictionary *optionsDict = NULL;
SDL_AudioSpec wanted_spec, spec;
if(stream_index < 0 || stream_index >= pFormatCtx->nb_streams) {
return -1;
}
// pCodecCtx 包含了这个流在用的编解码的所有信息，但我们仍需要通过他获得特定的解码器然后打开他。
codecCtx = pFormatCtx->streams[stream_index]->codec;
if(codecCtx->codec_type == AVMEDIA_TYPE_AUDIO) {
// Set audio settings from codec info
// 获取编解码信息设置音频
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;
// http://wiki.libsdl.org/SDL_OpenAudio
// 打开音频设备
if(SDL_OpenAudio(&wanted_spec, &spec) < 0) {
fprintf(stderr, "SDL_OpenAudio: %s\n", SDL_GetError());
return -1;
}
is->audio_hw_buf_size = spec.size;
}
// 为视频流获取特定的解码器。
codec = avcodec_find_decoder(codecCtx->codec_id);
// 打开解码器
if(!codec || (avcodec_open2(codecCtx, codec, &optionsDict) < 0)) {
fprintf(stderr, "Unsupported codec!\n");
return -1;
}
switch(codecCtx->codec_type) {
case AVMEDIA_TYPE_AUDIO: // 音频
is->audioStream = stream_index;
is->audio_st = pFormatCtx->streams[stream_index];
is->audio_buf_size = 0;
is->audio_buf_index = 0;
is->sws_ctx_audio = swr_alloc();
if (!is->sws_ctx_audio) {
fprintf(stderr, "Could not allocate resampler context\n");
return -1;
}
memset(&is->audio_pkt, 0, sizeof(is->audio_pkt));
packet_queue_init(&is->audioq); // 初始化音频队列
SDL_PauseAudio(0);
break;
case AVMEDIA_TYPE_VIDEO: // 视频
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); // 初始化视频队列
// 启动视频线程
is->video_tid = SDL_CreateThread(video_thread, is);
is->sws_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,
AV_PIX_FMT_YUV420P,
SWS_BILINEAR,
NULL,
NULL,
NULL
);
codecCtx->get_buffer2 = our_get_buffer;
//codecCtx->release_buffer = our_release_buffer;
break;
default:
break;
}
return 0;
}
int decode_interrupt_cb(void *opaque) {
return (global_video_state && global_video_state->quit);
}
int decode_thread(void *arg) {
// 上半部分的函数没什么新东西；它的工作就是打开文件和找到视频流和音频流的索引。
// 唯一不同的地方是把格式内容保存到大结构体中。当找到流后，调用另一个将要定义的函数 stream_component_open()。
// 这是一个一般的分离的方法，自从我们设置很多相似的视频和音频解码的代码，我们通过编写这个函数来重用它们。
VideoState *is = (VideoState *)arg;
AVFormatContext *pFormatCtx = NULL;
AVPacket pkt1, *packet = &pkt1;
// http://www.ffmpeg.org/doxygen/3.1/group__lavu__dict.html#details
AVDictionary *io_dict = NULL; // AVDictionary 元数据,Simple key:value store.
// http://www.ffmpeg.org/doxygen/3.1/structAVIOInterruptCB.html#details
AVIOInterruptCB callback; // Callback for checking whether to abort blocking functions.
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!
callback.callback = decode_interrupt_cb;
callback.opaque = is; // void * 类型
// http://www.ffmpeg.org/doxygen/3.1/aviobuf_8c.html#ae8589aae955d16ca228b6b9d66ced33d
// 使用is->filename的内容初始化is->io_context，用于管理文件的读写
if (avio_open2(&is->io_context, is->filename, 0, &callback, &io_dict))
{
fprintf(stderr, "Unable to open I/O for %s\n", is->filename);
return -1;
}
// 从传入的第二个参数获得文件路径，这个函数会读取文件头信息，并把信息保存在 pFormatCtx 结构体当中。
// 这个函数后面两个参数分别是： 指定文件格式、格式化选项，当我们设置为 NULL 或 0 时，libavformat 会自动完成这些工作。
if(avformat_open_input(&pFormatCtx, is->filename, NULL, NULL)!=0)
return -1; // Couldn't open file
is->pFormatCtx = pFormatCtx;
// Retrieve stream information
// 得到流信息
if(avformat_find_stream_info(pFormatCtx, NULL)<0)
return -1; // Couldn't find stream information
// Dump information about file onto standard error
// 这个函数填充了 pFormatCtx->streams 流信息， 可以通过 dump_format 把信息打印出来：
av_dump_format(pFormatCtx, 0, is->filename, 0);
// 查找一个音频和视频流
for(i=0; i<pFormatCtx->nb_streams; i++) {
if(pFormatCtx->streams[i]->codec->codec_type==AVMEDIA_TYPE_VIDEO &&
video_index < 0) {
video_index=i;
}
if(pFormatCtx->streams[i]->codec->codec_type==AVMEDIA_TYPE_AUDIO &&
audio_index < 0) {
audio_index=i;
}
}
// stream_component_open()函数的作用是找到解码器，设置音频参数，保存重要信息到大结构体中，然后启动音频和视频线程。
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
// 上面都是打开文件和找到视频流和音频流的索引等工作，下面才是主循环
for(;;) {
if(is->quit) {
break; //控制循环是否退出
}
// seek stuff goes here
if(is->audioq.size > MAX_AUDIOQ_SIZE ||
is->videoq.size > MAX_VIDEOQ_SIZE) {
SDL_Delay(10); // 当队列中数据比较多的时候，就等待10ms
continue;
}
// 读取码流中的音频若干帧或者视频一帧
if(av_read_frame(is->pFormatCtx, packet) < 0) {
if(is->pFormatCtx->pb->error == 0) {
SDL_Delay(100); // 如果没有读取到数据，同时没有出错，那么等待100ms然后继续
continue;
} else {
break;
}
}
// 获取到音视频包之后，放置到相应的队列
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 = 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);
}
av_strlcpy(is->filename, argv[1], 1024);
// 初始化为视频缓冲准备的锁（pictq）
// 因为一旦事件驱动调用视频函数， 视频函数会从 pictq 抽出预解码帧。
// 同时， 视频解码器会把信息放进去， 我们不知道那个动作会先发生。
is->pictq_mutex = SDL_CreateMutex();
is->pictq_cond = SDL_CreateCond();
// schedule_refresh 是一个将要定义的函数。它的动作是告诉系统在某个特定的毫秒数后弹出 FF_REFRESH_EVENT 事件。
schedule_refresh(is, 40);
// 生成一个新线程能完全访问原始进程中的内存，启动我们给的线程,在这种情况下， 调用 decode_thread()并与 VideoState 结构体连接。
is->parse_tid = SDL_CreateThread(decode_thread, is);
if(!is->parse_tid) {
av_free(is);
return -1;
}
// 处理事件循环
for(;;) {
SDL_WaitEvent(&event);
switch(event.type) {
case FF_QUIT_EVENT:
case SDL_QUIT:
is->quit = 1;
/*
* If the video has finished playing, then both the picture and
* audio queues are waiting for more data. Make them stop
* waiting and terminate normally.
*/
SDL_CondSignal(is->audioq.cond);
SDL_CondSignal(is->videoq.cond);
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;
}