Crappy discriminated union filtering

gistfile1.txt

let result = test parserStream video
    
let moov = List.find(function | MOOV(x) -> true | _ -> false) result

let sttsElements = 
    match moov with
        | MOOV(l) -> 
            List.filter (function | TRAK(_) -> true | _ -> false) l
                            |> List.map (function | TRAK(l) -> l)   
                            |> List.collect id                             
                            |> List.filter (function | MDIA(x) -> true | _ -> false)
                            |> List.map (function |MDIA(x) -> x)
                            |> List.collect id
                            |> List.filter (function | MINF(x) -> true | _ -> false)
                            |> List.map (function | MINF(x) -> x)
                            |> List.collect id
                            |> List.filter (function | STBL(x) -> true | _ -> false)
                            |> List.map (function | STBL(x) -> x)
                            |> List.collect id
                            |> List.filter(function | STTS(x) -> true | _ -> false)
                            |> List.map(function | STTS(x) -> x)

        | _ -> failwith "error"