音視頻有三種同步方式

• 標準時間同步
• 音頻時間同步
• 視頻時間同步

介紹第一種也是相對簡單的一種方式

1. 解碼獲取已播放時間
2. 根據記錄的開始時間和當前時間差值獲取實際播放的時間
3. 已播放的時間-實際播放的時間=延遲時間

視頻計算

//計算延遲
int64_t pts = av_frame_get_best_effort_timestamp(yuv_frame);
//轉換（不同時間基時間轉換）
int64_t time = av_rescale_q(pts,stream->time_base,AV_TIME_BASE_Q);
player_wait_for_frame(player,time,player->video_stream_index);

音頻計算

int64_t pts = packet->pts;
    if (pts != AV_NOPTS_VALUE) {
            player->audio_clock = av_rescale_q(pts, stream->time_base, AV_TIME_BASE_Q);
    //      av_q2d(stream->time_base) * pts;
            LOGI("player_write_audio - read from pts");
            player_wait_for_frame(player,player->audio_clock + AUDIO_TIME_ADJUST_US, 
            player->audio_stream_index);
        }

延遲計算

/**
 * 獲取視頻當前播放時間
 */
int64_t player_get_current_video_time(Player *player) {
    int64_t current_time = av_gettime();
    return current_time - player->start_time;
}
/**
 * 延遲
 */
void player_wait_for_frame(Player *player, int64_t stream_time,
        int stream_no) {
    pthread_mutex_lock(&player->mutex);
    for(;;){
        int64_t current_video_time = player_get_current_video_time(player);
        int64_t sleep_time = stream_time - current_video_time;
        if (sleep_time < -300000ll) {
            // 300 ms late
            //這段代碼對于300毫秒的處理我也不知道什么意思拭荤，拿過來用盅蝗，有大佬知道什么意思的可以回復一下，不勝感激剔蹋。
            int64_t new_value = player->start_time - sleep_time;
            LOGI("player_wait_for_frame[%d] correcting %f to %f because late",
                    stream_no, (av_gettime() - player->start_time) / 1000000.0,
                    (av_gettime() - new_value) / 1000000.0);

            player->start_time = new_value;
            pthread_cond_broadcast(&player->cond);
        }

        if (sleep_time <= MIN_SLEEP_TIME_US) {
            // We do not need to wait if time is slower then minimal sleep time
            break;
        }

        if (sleep_time > 500000ll) {
            // if sleep time is bigger then 500ms just sleep this 500ms
            // and check everything again
            sleep_time = 500000ll;
        }
        //等待指定時長
        int timeout_ret = pthread_cond_timeout_np(&player->cond,
                &player->mutex, sleep_time/1000ll);

        // just go further
        LOGI("player_wait_for_frame[%d] finish", stream_no);
    }
    pthread_mutex_unlock(&player->mutex);
}