Note that this function is not meant to be the sole scheduling mechanism
of a filtergraph, only a convenience function to help drain a filtergraph
in a balanced way under normal circumstances.
Also note that AVERROR_EOF does not mean that frames did not arrive on
some of the sinks during the process.
When there are multiple sink links, in case the requested link
returns an EOF, this may cause a filter to flush pending frames
which are sent to another sink link, although unrequested.
@return the return value of ff_request_frame(),
or AVERROR_EOF if all links returned AVERROR_EOF
Request a frame on the oldest sink link.
If the request returns AVERROR_EOF, try the next.
Note that this function is not meant to be the sole scheduling mechanism of a filtergraph, only a convenience function to help drain a filtergraph in a balanced way under normal circumstances.
Also note that AVERROR_EOF does not mean that frames did not arrive on some of the sinks during the process. When there are multiple sink links, in case the requested link returns an EOF, this may cause a filter to flush pending frames which are sent to another sink link, although unrequested.
@return the return value of ff_request_frame(), or AVERROR_EOF if all links returned AVERROR_EOF