GstAppSrcCallbacks.needData

Called when the appsrc needs more data. A buffer or EOS should be pushed to appsrc from this thread or another thread. @length is just a hint and when it is set to -1, any number of bytes can be pushed into @appsrc.

struct GstAppSrcCallbacks
extern (C)
void function(GstAppSrc* src, uint length, void* userData) needData;