[原]零基础学习视频解码之seek

现在，我们要添加一些功能，当你看不能倒带的电影，是不是很烦？ 那么函数av_seek_frame功能看起来是多么赏心悦目。

我们将让左，右箭头来回走在影片中通过一个小的向上和向下箭头很多，其中“三多一少”是10秒，“很多”为60秒。因此，我们需要设置我们的主循环，用来捕获击键。然而，当我们得到一个按键，就不能直接称之为函数av_seek_frame。我们所要做的是在我们的主解码循环中，decode_thread循环做相应的处理。

为了检测按键，我们先来看看，看看我们得到了一个SDL_KEYDOWN事件。然后我们检查，看看哪个键得到使用event.key.keysym.sym。一旦我们知道我们要seek哪一种方式，我们通过增加增量，从我们的新get_master_clock函数值计算新的时间。接着我们调用stream_seek函数来设置seek_pos等值。我们新的时间转换为avcodec中的内部时间戳单元。回想一下，时间戳在流测量中的帧，而不是秒，于是秒=帧*time_base（fps）。 avcodec中默认为1,000,000 fps的值（这样的2秒的POS将是2000000时间戳）。

现在，让我们去到我们的decode_thread，我们将实际执行我们的seek。你会发现在我们已经标志着一个区域的源文件“seek的东西放在这里”，好了，我们打算把它放在那里了。
seek的函数av_seek_frame，该函数将seek到给它的时间戳。时间戳的单位是传递函数的流的基本time_base。但是，你不必把它传递一个流（通过传递值-1表示）。如果你这样做，那么time_base将是avcodec中的内部时间戳单位，或者1000000fps。这就是为什么当我们设置seek_pos乘AV_TIME_BASE。

av_rescale_q（A，B，C）是将重新调整时间戳从一个基地到另一个函数。它基本上是计算A * B/ C，但这个功能是必需的，因为计算可能溢出。 AV_TIME_BASE_Q是AV_TIME_BASE的小数版本。他们是完全不同的：AV_TIME_BASE* time_in_seconds= avcodec_timestamp和AV_TIME_BASE_Q* avcodec_timestamp= time_in_seconds（但要注意，AV_TIME_BASE_Q实际上是一个AVRational对象，所以你必须要使用特殊的q函数在avcodec中处理它）。

是的，但我们没有完成很呢。请记住，我们有一个队列设置了累积的数据包。现在，我们在不同的地方，我们要刷新的队列不是要去seek！不仅如此，avcodec中它自己内部的各缓冲器的需要由每个线程去刷新。

要做到这一点，我们需要先写一个函数来清除我们的数据包队列。然后，我们需要有指示音频和视频线，他们需要刷新avcodec中的内部缓冲器的一些方式。我们可以通过把一种特殊的数据包队列后，而当他们发现了特殊的包，他们就会刷新自己的缓冲区。

/*
 ============================================================================
 Name        : VideoDecodeTutorial7_1.c
 Author      : clarck
 Version     :
 Copyright   : Your copyright notice
 Description : Hello World in C, Ansi-style
 ============================================================================
 */
#include <libavcodec/avcodec.h>
#include <libavformat/avformat.h>
#include <libavformat/avio.h>
#include <libswscale/swscale.h>
#include <libavutil/avstring.h>
#include <libavutil/mathematics.h>
#include <libavutil/time.h>

#include <SDL/SDL.h>
#include <SDL/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_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 SAMPLE_CORRECTION_PERCENT_MAX 10
#define AUDIO_DIFF_AVG_NB 20

#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 DEFAULT_AV_SYNC_TYPE AV_SYNC_VIDEO_MASTER
#define AVCODEC_MAX_AUDIO_FRAME_SIZE 192000 // 1 second of 48khz 32bit audio

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;

    int av_sync_type;
    double external_clock; /* external clock base */
    int64_t external_clock_time;

    int seek_req;
    int seek_flags;
    int64_t seek_pos;

    double audio_clock;
    AVStream *audio_st;
    PacketQueue audioq;
    uint8_t audio_buf[(AVCODEC_MAX_AUDIO_FRAME_SIZE * ) / ];
    unsigned int audio_buf_size;
    unsigned int audio_buf_index;
    AVPacket audio_pkt;
    uint8_t *audio_pkt_data;
    int audio_pkt_size;
    AVFrame audio_frame;
    AVStream *video_st;
    PacketQueue videoq;
    int audio_hw_buf_size;
    double audio_diff_cum; /* used for AV difference average computation */
    double audio_diff_avg_coef;
    double audio_diff_threshold;
    int audio_diff_avg_count;
    double frame_timer;
    double frame_last_pts;
    double frame_last_delay;

    double video_current_pts; ///<current displayed pts (different from video_clock if frame fifos are used)
    int64_t video_current_pts_time; ///<time (av_gettime) at which we updated video_current_pts - used to have running video pts

    double video_clock; ///<pts of last decoded frame / predicted pts of next decoded frame

    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;

    AVIOContext *io_ctx;
    struct SwsContext *sws_ctx;

    char filename[];
    int quit;
} VideoState;

enum {
    AV_SYNC_AUDIO_MASTER, AV_SYNC_VIDEO_MASTER, AV_SYNC_EXTERNAL_MASTER,
};

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;

AVPacket flush_pkt;

void packet_queue_init(PacketQueue *q) {
    memset(q, , sizeof(PacketQueue));
    q->mutex = SDL_CreateMutex();
    q->cond = SDL_CreateCond();
}
int packet_queue_put(PacketQueue *q, AVPacket *pkt) {

    AVPacketList *pkt1;
    if (pkt != &flush_pkt && av_dup_packet(pkt) < ) {
        return -;
    }
    pkt1 = av_malloc(sizeof(AVPacketList));
    if (!pkt1)
        return -;
    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 ;
}
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 = -;
            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 = ;
            break;
        } else if (!block) {
            ret = ;
            break;
        } else {
            SDL_CondWait(q->cond, q->mutex);
        }
    }
    SDL_UnlockMutex(q->mutex);
    return ret;
}

static void packet_queue_flush(PacketQueue *q) {
    AVPacketList *pkt, *pkt1;

    SDL_LockMutex(q->mutex);
    for (pkt = q->first_pkt; pkt != NULL; pkt = pkt1) {
        pkt1 = pkt->next;
        av_free_packet(&pkt->pkt);
        av_freep(&pkt);
    }
    q->last_pkt = NULL;
    q->first_pkt = NULL;
    q->nb_packets = ;
    q->size = ;
    SDL_UnlockMutex(q->mutex);
}

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 = ;
    n = is->audio_st->codec->channels * ;
    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;
}

double get_video_clock(VideoState *is) {
    double delta;

    delta = (av_gettime() - is->video_current_pts_time) / 1000000.0;
    return is->video_current_pts + delta;
}
double get_external_clock(VideoState *is) {
    return av_gettime() / 1000000.0;
}

double get_master_clock(VideoState *is) {
    if (is->av_sync_type == AV_SYNC_VIDEO_MASTER) {
        return get_video_clock(is);
    } else if (is->av_sync_type == AV_SYNC_AUDIO_MASTER) {
        return get_audio_clock(is);
    } else {
        return get_external_clock(is);
    }
}
/* Add or subtract samples to get a better sync, return new
 audio buffer size */
int synchronize_audio(VideoState *is, short *samples, int samples_size,
        double pts) {
    int n;
    double ref_clock;

    n =  * is->audio_st->codec->channels;

    if (is->av_sync_type != AV_SYNC_AUDIO_MASTER) {
        double diff, avg_diff;
        int wanted_size, min_size, max_size;
        //int nb_samples;

        ref_clock = get_master_clock(is);
        diff = get_audio_clock(is) - ref_clock;

        if (diff < AV_NOSYNC_THRESHOLD) {
            // accumulate the diffs
            is->audio_diff_cum = diff
                    + is->audio_diff_avg_coef * is->audio_diff_cum;
            if (is->audio_diff_avg_count < AUDIO_DIFF_AVG_NB) {
                is->audio_diff_avg_count++;
            } else {
                avg_diff = is->audio_diff_cum * (1.0 - is->audio_diff_avg_coef);
                if (fabs(avg_diff) >= is->audio_diff_threshold) {
                    wanted_size = samples_size
                            + ((int) (diff * is->audio_st->codec->sample_rate)
                                    * n);
                    min_size = samples_size
                            * (( - SAMPLE_CORRECTION_PERCENT_MAX) / );
                    max_size = samples_size
                            * (( + SAMPLE_CORRECTION_PERCENT_MAX) / );
                    if (wanted_size < min_size) {
                        wanted_size = min_size;
                    } else if (wanted_size > max_size) {
                        wanted_size = max_size;
                    }
                    if (wanted_size < samples_size) {
                        /* remove samples */
                        samples_size = wanted_size;
                    } else if (wanted_size > samples_size) {
                        uint8_t *samples_end, *q;
                        int nb;

                        /* add samples by copying final sample*/
                        nb = (samples_size - wanted_size);
                        samples_end = (uint8_t *) samples + samples_size - n;
                        q = samples_end + n;
                        while (nb > ) {
                            memcpy(q, samples_end, n);
                            q += n;
                            nb -= n;
                        }
                        samples_size = wanted_size;
                    }
                }
            }
        } else {
            /* difference is TOO big; reset diff stuff */
            is->audio_diff_avg_count = ;
            is->audio_diff_cum = ;
        }
    }
    return samples_size;
}

int audio_decode_frame(VideoState *is, double *pts_ptr) {

    int len1, data_size = , n;
    AVPacket *pkt = &is->audio_pkt;
    double pts;

    for (;;) {
        while (is->audio_pkt_size > ) {
            int got_frame = ;
            len1 = avcodec_decode_audio4(is->audio_st->codec, &is->audio_frame,
                    &got_frame, pkt);
            if (len1 < ) {
                /* if error, skip frame */
                is->audio_pkt_size = ;
                break;
            }

            if (got_frame) {
                data_size = is->audio_frame.linesize[];
                /*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[], data_size);
            }

            is->audio_pkt_data += len1;
            is->audio_pkt_size -= len1;
            if (data_size <= ) {
                /* No data yet, get more frames */
                continue;
            }

            pts = is->audio_clock;
            *pts_ptr = pts;
            n =  * 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 -;
        }
        /* next packet */
        if (packet_queue_get(&is->audioq, pkt, ) < ) {
            return -;
        }

        if (pkt->data == flush_pkt.data) {
            avcodec_flush_buffers(is->audio_st->codec);
            continue;
        }

        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;
        }
    }

    return ;
}

void audio_callback(void *userdata, Uint8 *stream, int len) {

    VideoState *is = (VideoState *) userdata;
    int len1, audio_size;
    double pts;

    while (len > ) {
        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 < ) {
                /* If error, output silence */
                is->audio_buf_size = ;
                memset(is->audio_buf, , is->audio_buf_size);
            } else {
                audio_size = synchronize_audio(is, (int16_t *) is->audio_buf,
                        audio_size, pts);
                is->audio_buf_size = audio_size;
            }
            is->audio_buf_index = ;
        }
        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 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;
    float aspect_ratio;
    int w, h, x, y;

    vp = &is->pictq[is->pictq_rindex];
    if (vp->bmp) {
        if (is->video_st->codec->sample_aspect_ratio.num == ) {
            aspect_ratio = ;
        } 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)) & -;
        if (w > screen->w) {
            w = screen->w;
            h = ((int) rint(w / aspect_ratio)) & -;
        }
        x = (screen->w - w) / ;
        y = (screen->h - h) / ;

        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 == ) {
            schedule_refresh(is, );
        } else {

            vp = &is->pictq[is->pictq_rindex];

            is->video_current_pts = vp->pts;
            is->video_current_pts_time = av_gettime();

            delay = vp->pts - is->frame_last_pts; /* the pts from last time */
            if (delay <=  || 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;

            /* update delay to sync to audio if not master source */
            if (is->av_sync_type != AV_SYNC_VIDEO_MASTER) {
                ref_clock = get_master_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 = ;
                    } else if (diff >= sync_threshold) {
                        delay =  * 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 *  + 0.5));

            /* show the picture! */
            video_display(is);

            /* update queue for next picture! */
            if (++is->pictq_rindex == VIDEO_PICTURE_QUEUE_SIZE) {
                is->pictq_rindex = ;
            }
            SDL_LockMutex(is->pictq_mutex);
            is->pictq_size--;
            SDL_CondSignal(is->pictq_cond);
            SDL_UnlockMutex(is->pictq_mutex);
        }
    } else {
        schedule_refresh(is, );
    }
}

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 = ;
    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 -;

    // 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 = ;
        /* 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 -;
        }
    }
    /* 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);

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

        pict.data[] = vp->bmp->pixels[];
        pict.data[] = vp->bmp->pixels[];
        pict.data[] = vp->bmp->pixels[];

        pict.linesize[] = vp->bmp->pitches[];
        pict.linesize[] = vp->bmp->pitches[];
        pict.linesize[] = vp->bmp->pitches[];

        // Convert the image into YUV format that SDL uses
        sws_scale(is->sws_ctx, (const uint8_t * const *) pFrame->data,
                pFrame->linesize, , 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 = ;
        }
        SDL_LockMutex(is->pictq_mutex);
        is->pictq_size++;
        SDL_UnlockMutex(is->pictq_mutex);
    }
    return ;
}

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

    double frame_delay;

    if (pts != ) {
        /* 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 len1;
    int frameFinished;
    AVFrame *pFrame;
    double pts;

    pFrame = av_frame_alloc();

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

        pts = ;

        // Save global pts to be stored in pFrame in first call
        global_video_pkt_pts = packet->pts;

        // Decode video frame
        //len1 =
        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 = ;
        }
        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) < ) {
                break;
            }
        }
        av_free_packet(packet);
    }
    av_free(pFrame);
    return ;
}

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 <  || stream_index >= pFormatCtx->nb_streams) {
        return -;
    }

    // Get a pointer to the codec context for the video stream
    codecCtx = pFormatCtx->streams[stream_index]->codec;

    if (codecCtx->codec_type == AVMEDIA_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 = ;
        wanted_spec.samples = SDL_AUDIO_BUFFER_SIZE;
        wanted_spec.callback = audio_callback;
        wanted_spec.userdata = is;

        if (SDL_OpenAudio(&wanted_spec, &spec) < ) {
            fprintf(stderr, "SDL_OpenAudio: %s\n", SDL_GetError());
            return -;
        }
        is->audio_hw_buf_size = spec.size;
    }
    codec = avcodec_find_decoder(codecCtx->codec_id);
    if (!codec || (avcodec_open2(codecCtx, codec, NULL) < )) {
        fprintf(stderr, "Unsupported codec!\n");
        return -;
    }

    switch (codecCtx->codec_type) {
    case AVMEDIA_TYPE_AUDIO:
        is->audioStream = stream_index;
        is->audio_st = pFormatCtx->streams[stream_index];
        is->audio_buf_size = ;
        is->audio_buf_index = ;

        /* averaging filter for audio sync */
        is->audio_diff_avg_coef = exp(log(0.01 / AUDIO_DIFF_AVG_NB));
        is->audio_diff_avg_count = ;
        /* Correct audio only if larger error than this */
        is->audio_diff_threshold = 2.0 * SDL_AUDIO_BUFFER_SIZE
                / codecCtx->sample_rate;

        memset(&is->audio_pkt, , sizeof(is->audio_pkt));
        packet_queue_init(&is->audioq);
        SDL_PauseAudio();
        break;
    case AVMEDIA_TYPE_VIDEO:
        is->videoStream = stream_index;
        is->video_st = pFormatCtx->streams[stream_index];

        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_FAST_BILINEAR, NULL, NULL, NULL);

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

        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 ;
}

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

int decode_thread(void *arg) {

    VideoState *is = (VideoState *) arg;
    AVFormatContext *pFormatCtx = NULL;
    AVPacket pkt1, *packet = &pkt1;

    int video_index = -;
    int audio_index = -;
    int i;

    is->videoStream = -;
    is->audioStream = -;

    AVIOInterruptCB interupt_cb;

    global_video_state = is;

    // will interrupt blocking functions if we quit!
    interupt_cb.callback = decode_interrupt_cb;
    interupt_cb.opaque = is;
    if (avio_open2(&is->io_ctx, is->filename, , &interupt_cb, NULL)) {
        fprintf(stderr, "Cannot open I/O for %s\n", is->filename);
        return -;
    }

    // Open video file
    if (avformat_open_input(&pFormatCtx, is->filename, NULL, NULL) != )
        return -; // Couldn't open file

    is->pFormatCtx = pFormatCtx;

    // Retrieve stream information
    if (avformat_find_stream_info(pFormatCtx, NULL) < )
        return -; // Couldn't find stream information

    // Dump information about file onto standard error
    av_dump_format(pFormatCtx, , is->filename, );

    // Find the first video stream

    for (i = ; i < pFormatCtx->nb_streams; i++) {
        if (pFormatCtx->streams[i]->codec->codec_type == AVMEDIA_TYPE_VIDEO
                && video_index < ) {
            video_index = i;
        }
        if (pFormatCtx->streams[i]->codec->codec_type == AVMEDIA_TYPE_AUDIO
                && audio_index < ) {
            audio_index = i;
        }
    }
    if (audio_index >= ) {
        stream_component_open(is, audio_index);
    }
    if (video_index >= ) {
        stream_component_open(is, video_index);
    }

    if (is->videoStream <  || is->audioStream < ) {
        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->seek_req) {
            int stream_index = -;
            int64_t seek_target = is->seek_pos;

            if (is->videoStream >= )
                stream_index = is->videoStream;
            else if (is->audioStream >= )
                stream_index = is->audioStream;

            if (stream_index >= ) {
                seek_target = av_rescale_q(seek_target, AV_TIME_BASE_Q,
                        pFormatCtx->streams[stream_index]->time_base);
            }
            if (av_seek_frame(is->pFormatCtx, stream_index, seek_target,
                    is->seek_flags) < ) {
                fprintf(stderr, "%s: error while seeking\n",
                        is->pFormatCtx->filename);
            } else {
                if (is->audioStream >= ) {
                    packet_queue_flush(&is->audioq);
                    packet_queue_put(&is->audioq, &flush_pkt);
                }
                if (is->videoStream >= ) {
                    packet_queue_flush(&is->videoq);
                    packet_queue_put(&is->videoq, &flush_pkt);
                }
            }
            is->seek_req = ;
        }

        if (is->audioq.size > MAX_AUDIOQ_SIZE
                || is->videoq.size > MAX_VIDEOQ_SIZE) {
            SDL_Delay();
            continue;
        }

        if (av_read_frame(is->pFormatCtx, packet) < ) {
            if (is->pFormatCtx->pb->error == ) {
                SDL_Delay(); /* 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();
    }

    fail: {
        SDL_Event event;
        event.type = FF_QUIT_EVENT;
        event.user.data1 = is;
        SDL_PushEvent(&event);
    }
    return ;
}

void stream_seek(VideoState *is, int64_t pos, int rel) {

    if (!is->seek_req) {
        is->seek_pos = pos;
        is->seek_flags = rel <  ? AVSEEK_FLAG_BACKWARD : ;
        is->seek_req = ;
    }
}

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

    SDL_Event event;
    //double pts;
    VideoState *is;

    is = av_mallocz(sizeof(VideoState));
    char filePath[] = "./src/a.mp4";

    // 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();
    }

    // Make a screen to put our video
#ifndef __DARWIN__
    screen = SDL_SetVideoMode(, , , );
#else
    screen = SDL_SetVideoMode(, , , );
#endif
    if (!screen) {
        fprintf(stderr, "SDL: could not set video mode - exiting\n");
        exit();
    }

    av_strlcpy(is->filename, filePath, sizeof(is->filename));

    is->pictq_mutex = SDL_CreateMutex();
    is->pictq_cond = SDL_CreateCond();

    schedule_refresh(is, );

    is->av_sync_type = DEFAULT_AV_SYNC_TYPE;

    is->parse_tid = SDL_CreateThread(decode_thread, is);
    if (!is->parse_tid) {
        av_free(is);
        return -;
    }
    av_init_packet(&flush_pkt);
    flush_pkt.data = (unsigned char *) "FLUSH";
    for (;;) {
        double incr, pos;
        SDL_WaitEvent(&event);
        switch (event.type) {
        case SDL_KEYDOWN:
            switch (event.key.keysym.sym) {
            case SDLK_LEFT:
                incr = -10.0;
                goto do_seek;
            case SDLK_RIGHT:
                incr = 10.0;
                goto do_seek;
            case SDLK_UP:
                incr = 60.0;
                goto do_seek;
            case SDLK_DOWN:
                incr = -60.0;
                goto do_seek;
                do_seek: if (global_video_state) {
                    pos = get_master_clock(global_video_state);
                    pos += incr;
                    stream_seek(global_video_state,
                            (int64_t) (pos * AV_TIME_BASE), incr);
                }
                break;
            default:
                break;
            }
            break;
        case FF_QUIT_EVENT:
        case SDL_QUIT:
            SDL_CondSignal(is->audioq.cond);
            SDL_CondSignal(is->videoq.cond);
            is->quit = ;
            SDL_Quit();
            exit();
            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 ;

}