av_get_sample_fmt_string

Generate a string corresponding to the sample format with sample_fmt, or a header if sample_fmt is negative.

@param buf the buffer where to write the string @param buf_size the size of buf @param sample_fmt the number of the sample format to print the corresponding info string, or a negative value to print the corresponding header. @return the pointer to the filled buffer or NULL if sample_fmt is unknown or in case of other errors