VLC-Android视频显示流程

最近在做MEMC调试涉及到了播放器刷帧频率的问题，因此深入研究了一下VLC视频的显示流程，仔细研究过后发现还是有挺多坑的，在这里分享下：

VLC的视频显示逻辑主要在video_output.c中，其内部维护了一个线程用来接收control和刷新显示（这里和ijkplayer很像）：

//vout中其实有两个线程，分别名为Thread和ThreadStep，视频正常播放走的是Thread，步进播放走的是ThreadStep（类似ffplay的s键），这里主要还是介绍Thread /*****************************************************************************  * Thread: video output thread  *****************************************************************************  * Video output thread. This function does only returns when the thread is  * terminated. It handles the pictures arriving in the video heap and the  * display device events.  *****************************************************************************/ static void *Thread(void *object) {     vout_thread_t *vout = object;     vout_thread_sys_t *sys = vout->p;     mtime_t deadline = VLC_TS_INVALID;     bool wait = false;     //这里是一个大的死循环     for (;;) {         vout_control_cmd_t cmd;         //对deadline进行修正         if (wait)         {             const mtime_t max_deadline = mdate() + 100000;             deadline = deadline <= VLC_TS_INVALID ? max_deadline : __MIN(deadline, max_deadline);         } else {             deadline = VLC_TS_INVALID;         }         //处理control         while (!vout_control_Pop(&sys->control, &cmd, deadline))             if (ThreadControl(vout, cmd))                 return NULL;         //显示Picture         deadline = VLC_TS_INVALID;         wait = ThreadDisplayPicture(vout, &deadline) != VLC_SUCCESS;         const bool picture_interlaced = sys->displayed.is_interlaced;         vout_SetInterlacingState(vout, picture_interlaced);         vout_ManageWrapper(vout);     } }

Thread调用ThreadDisplayPicture刷新显示：

static int ThreadDisplayPicture(vout_thread_t *vout, mtime_t *deadline) {     bool frame_by_frame = !deadline;     bool paused = vout->p->pause.is_on;     //vout->p->displayed.current代表当前正在播放的帧（类比ffplay video_refresh函数中的lastvp）     bool first = !vout->p->displayed.current;     //调用ThreadDisplayPreparePicture准备一帧     if (first)         if (ThreadDisplayPreparePicture(vout, true, frame_by_frame)) /* FIXME not sure it is ok */             return VLC_EGENERIC;     //vout->p->displayed.next代表要播放的下一帧（类比ffplay video_refresh函数中的vp）     if (!paused || frame_by_frame)         while (!vout->p->displayed.next && !ThreadDisplayPreparePicture(vout, false, frame_by_frame))             ;     const mtime_t date = mdate();     //这里计算render_delay来决定要提前多久显示     //这里补充说明一点，Google在MediaCodec.java中建议提前两个VSYNC时间显示，原因可以自行百度Android的VSYNC显示机制