freebayes VCF output (FREQ header)

Question

[Thomas]

Hello,

I need to use freebayes to generate a VCF file which has a particular format, namely the file should contain the following line in the header section:

FORMAT=<id=freq,number=1,type=string,description="variant allele="" frequency"="">

However, because freebayes contains a large number of options, I am not sure which options to specify in order to generate this particular type of output, or whether it is possible to generate this header file using freebayes

Thanks