Ardour script to export all range markers in a session

export_range_markers.lua

ardour {
    type = "EditorAction",
    name = "Export all range markers as a JSON array",
    author = "Andrew Anderson",
    description = [[
Writes the name, start, and end (in hh:mm:ss format) of all range markers to
the file `export/range_markers.json`
]],
    license = "MIT",
}

-- Timestamp conversion code is adapted from
-- https://github.com/Ardour/ardour/blob/master/share/scripts/export_mp4chaps.lua
-- Author: Johannes Mueller
-- License: GPLv2
function format_timepos(pos)
    local fr = Session:sample_rate()
    local t = pos:samples()
    local h = math.floor(t / (3600*fr))
    local r = t - (h*3600*fr)
    local m = math.floor(r / (60*fr))
    r = r - m*60*fr
    local s = math.floor(r / fr)
    r = r - s*fr
    local ms = math.floor(r*1000/fr)

    return string.format("%02d:%02d:%02d.%03d", h, m, s, ms)
end

function get_ranges()
    local ranges = {}

    for l in Session:locations():list():iter() do
        if l:is_range_marker() then
            local name = l:name()
            local start_formatted = format_timepos(l:start())
            local end_formatted = format_timepos(l:_end())

            local range = {
                name = name,
                start = start_formatted,
                _end = end_formatted
            }
            table.insert(ranges, range)
        end
    end

    return ranges
end

function escape_json_string(s)
    return s:gsub('"', '\\"')
end

function format_range_as_json_object(range)
    return string.format(
        '{"name": "%s", "start": "%s", "end": "%s"}',
        escape_json_string(range.name),
        range.start,
        range._end
    )
end

function factory(unused_params)
    return function()
         local ranges = get_ranges()
         local path = ARDOUR.LuaAPI.build_filename(
             Session:path(),
             "export",
             "range_markers.json"
         )
         local file = io.open(path, "w")

         file:write("[")
         for i, range in ipairs(ranges) do
             if i > 1 then
                 file:write(",")
             end
             local obj = format_range_as_json_object(range)
             file:write(obj)
         end
         file:write("]")
         file:close()
    end
end