What do the ending numbers (e.g., Db 1; Db/F 1/3) written below the chords mean?

What do the ending numbers written below the chord in this video really mean?

Db 1, Db/F 1/3, Gb 4, Ab 5, Db 1, Db/F 1/3, Gb 4, Ab 5,

Fm7 3m, Bbm7 6m, Gb 4, Ab sus 5 sus, Ab7 5, Fm7 3m, Bbm7 6m, Gb 4, Ab sus 5 sus, Ab 5,

Db 1, Ab 5, Bbm7 6m, Gb 4, Db 1, Ab 5, Gb 4, Ab 5, ...

• Db means the D flat triad. But what does 1 mean? Is that the keynote pitch? (like the middle C is C4?) or is that tempo?

• Db/F 1/3 means the inverted D flat triad with the starting F base. But what does 1/3 mean? Is that the keynote pitch?

This is Nashville chord notation system https://en.wikipedia.org/wiki/Nashville_Number_System

The numbers refer to the scale steps on which the chords are built.

The song is in the key of Db major. 1 means chord built on the first step, Db major. 1/3 means Db chord with 3rd scale degree in bass, F. 3m is a minor chord built on the 3rd scale degree, F minor. 4 is a chord built on 4th scale degree, Gb major – and so on.

It is an alternative chord notation, so you can use either regular chord symbols (Db, Db/F, Fm, Gb...), or Nashville numbers, they carry the same information.

It is indeed the NNS - Nashville Number System. Each chord in a key is given a number, corresponding to the note number in that key. Here, in D♭ - D♭ =1, E♭ = 2, F = 3, G♭ = 4, A♭ = 5, and B♭ = 6.

That may seem to be extra stuff for little purpose - just write the perishing chords, please!

But, the idea is far reaching. In the recording studio, for example, the musos turn up, and the song is already written. Musos though, don't know the best key for it. So with just NNS, they can play it immediately in any key. For example, the first 3 chords - 1, 1/3, 4 in key C are C, C/E F; in key G, G, G/B, C, in key A, A, A/C♯, D. Much quicker than re-writing the chart !