从接收到数据流到播放视频的过程分析
从网络接收到流->对数据流进行视频和音频分离->对视频用解码器解码->显示解码后的视频流
视频显示部分走势线：分离->解码->新的VOUT缓冲区->VOUT线程
Demux(modules\demux\mpeg\ps.c)->DemuxPs(modules\demux\mpeg\system.c)-> ParsePS->input_SelectES(src\input\input_programs.c)->input_RunDecoder(src\input\input_dec.c)->CreateDecoder->
vout_new_buffer->vout_Request(src\video_output\video_output.c)->vout_Create->RunThread->vout_RenderPicture(src\video_output\vout_pictures.c)->pf_display
注意：p_dec->pf_vout_buffer_new = vout_new_buffer的pf_vout_buffer_new在ffmpeg_NewPictBuf（modules\codec\ffmpeg\video.c）函数中激活
解码部分走势线：
Demux(modules\demux\mpeg\ps.c)->DemuxPs(modules\demux\mpeg\system.c)-> ParsePS->input_SelectES(src\input\input_programs.c)->input_RunDecoder(src\input\input_dec.c)->CreateDecoder->
DecoderThread
注意：在解码线程中对数据流（AUDIO 或者VIDEO）进行解码
详细资料 http://developers.videolan.org/vlc/ VLC API documentation 或者VLC developer documentation
Chapter 5. The video output layer
Data structures and main loop
Important data structures are defined in include/video.h and include/video_output.h. The main data structure is picture_t, which describes everything a video decoder thread needs. Please refer to this file for more information. Typically, p_data will be a pointer to YUV planar picture.
Note also the subpicture_t structure. In fact the VLC SPU decoder only parses the SPU header, and converts the SPU graphical data to an internal format which can be rendered much faster. So a part of the "real" SPU decoder lies in src/video_output/video_spu.c.
The vout_thread_t structure is much more complex, but you needn't understand everything. Basically the video output thread manages a heap of pictures and subpictures (5 by default). Every picture has a status (displayed, destroyed, empty...) and eventually a presentation time. The main job of the video output is an infinite loop to : [this is subject to change in the near future]
Find the next picture to display in the heap.
Find the current subpicture to display.
Render the picture (if the video output plug-in doesn't support YUV overlay). Rendering will call an optimized YUV plug-in, which will also do the scaling, add subtitles and an optional picture information field.
Sleep until the specified date.
Display the picture (plug-in function). For outputs which display RGB data, it is often accomplished with a buffer switching. p_vout->p_buffer is an array of two buffers where the YUV transform takes place, and p_vout->i_buffer_index indicates the currently displayed buffer.
Manage events.
Methods used by video decoders
The video output exports a bunch of functions so that decoders can send their decoded data. The most important function is vout_CreatePicture which allocates the picture buffer to the size indicated by the video decoder. It then just needs to feed (void *) p_picture->p_data with the decoded data, and call vout_DisplayPicture and vout_DatePicture upon necessary.
picture_t * vout_CreatePicture ( vout_thread_t *p_vout, int i_type, int i_width, int i_height ) : Returns an allocated picture buffer. i_type will be for instance YUV_420_PICTURE, and i_width and i_height are in pixels.
Warning
If no picture is available in the heap, vout_CreatePicture will return NULL.
vout_LinkPicture ( vout_thread_t *p_vout, picture_t *p_pic ) : Increases the refcount of the picture, so that it doesn't get accidently freed while the decoder still needs it. For instance, an I or P picture can still be needed after displaying to decode interleaved B pictures.
vout_UnlinkPicture ( vout_thread_t *p_vout, picture_t *p_pic ) : Decreases the refcount of the picture. An unlink must be done for every link previously made.
vout_DatePicture ( vout_thread_t *p_vout, picture_t *p_pic ) : Gives the picture a presentation date. You can start working on a picture before knowing precisely at what time it will be displayed. For instance to date an I or P picture, you must wait until you have decoded all previous B pictures (which are indeed placed after - decoding order != presentation order).
vout_DisplayPicture ( vout_thread_t *p_vout, picture_t *p_pic ) : Tells the video output that a picture has been completely decoded and is ready to be rendered. It can be called before or after vout_DatePicture.
vout_DestroyPicture ( vout_thread_t *p_vout, picture_t *p_pic ) : Marks the picture as empty (useful in case of a stream parsing error).
subpicture_t * vout_CreateSubPicture ( vout_thread_t *p_vout, int i_channel, int i_type ) : Returns an allocated subpicture buffer. i_channel is the ID of the subpicture channel, i_type is DVD_SUBPICTURE or TEXT_SUBPICTURE, i_size is the length in bytes of the packet.
vout_DisplaySubPicture ( vout_thread_t *p_vout, subpicture_t *p_subpic ) : Tells the video output that a subpicture has been completely decoded. It obsoletes the previous subpicture.
vout_DestroySubPicture ( vout_thread_t *p_vout, subpicture_t *p_subpic ) : Marks the subpicture as empty.
