* src/video_output/vout_pictures.c, include/video_output.h: added a vout_InitPicture() function that initializes a picture_t structure based on the given chroma and sizes.
* modules/encoder/ffmpeg/video.c: misc improvements. Should also be able to handle more input chroma format.
* modules/codec/rawvideo.c: a few fixes.
* modules/access/v4l/v4l.c: misc improvments and cleanup. Should be able to handle more source chroma formats. On the fly video encoding is also working perfectly now.