https://www.accesstoinsight.org/tipitak ... .vaji.html
Because rapture and sukha are feelings, we assume the meditator is “oneself having form”.Eight Liberations
33. "Now there are eight liberations, Ananda. What are those eight? 
34. "Oneself having form,  one perceives forms; this is the first liberation.
That he is outwardly intent on outer forms (ie. “one perceives forms”) the meditator is not simply in a state of mindfulness; but rather aloof from the ordinary trappings of bodily sensation that both keep him inwardly introspective and prevent him from adopting a form of concentration that looks outwards and fixates on external forms.
The second liberation, (IMHO) refers to what one experiences in the fourth jhana. The supramundane feature of the fourth jhana is “adukkhaasukkha” (often mistranslated as “a neutral feeling”; when it should be translated as “that which goes beyond both pleasure and pain”. If not this, then what is the upward trajectory of a jhana which excludes rapture and bliss instead for a simple “neutral” feeling? That makes no sense.)
Adukkhaasukkha should be more sublime even than the bliss felt in the third jhana. For that reason the fourth jhana is the basis of the second liberation. Here:
Adukkhaasukkha transcends bodily feeling altogether, and thus he is unaware of his own form; and equanimity establishes his fixed and focused concentration on outward forms.35. "Being unaware of one's own form, one perceives forms external to oneself; this is the second liberation.
Thence, the very basic quality of achieving samadhi in any of the first three rupa jhanas is a liberation in itself and an attainment of samadhi in the fourth jhana is a second higher liberation in and of itself.