diff --git a/filters.nu b/filters.nu
index 175caaf..d312921 100755
--- a/filters.nu
+++ b/filters.nu
@@ -1,16 +1,31 @@
 #!/usr/bin/env -S nu --stdin
 
 export def "parse filter" [
-] {
-  $in | parse --regex '^(?<name>[^=]+)=(?<params>.*)' | first |
-  update params { parse --regex `(?<param>[^=]+)=(?<value>[^:]+):?` }
+]: string -> table<name: string params: table<param: string, value: string>> {
+  $in | parse --regex '^(?<name>[^=]+)=(?<params>.*)' | first | update params {
+    parse --regex `(?<param>[^=]+)=(?<value>[^:]+):?`
+  }
 }
 
-export def "filter to-string" [] {
-  each { |filter| $'($filter.name)=($filter.params | format '{param}={value}')' } |
-  str join ':'
+export def "filter to-string" [
+]: table<name: string params: table<param: string, value: string>> -> string {
+  each {
+    $'($in.name)=($in.params | format '{param}={value}')'
+  } | str join ':'
 }
 
+# Build a record representaion of a complex filter
+export def complex-filter [
+  name: string
+  params: record = {}
+]: nothing -> record<name: string params: table<param: string, value: string>> {
+  {
+    name: $name
+    params: ($params | transpose param value | compact param value)
+  }
+}
+
+
 export def "complex-filters to-string" [
   --pretty-print (-p)
 ]: table<input: list<string>, filters: table<name: string, params: table<param: string, value: string>>, output: string> -> string {
@@ -20,3 +35,22 @@ export def "complex-filters to-string" [
       str join ']['
     } | format '[{input}]{filters}[{output}]' | str join (";" + (if $pretty_print { "\n"  } else { "" })) | str replace --all '[]' ''
 }
+
+# =============
+# Begin Filters
+# =============
+
+# loop video frames
+export def loop [
+  loop: int # Set the number of loops. Setting this value to -1 will result in infinite loops. Default is 0.
+  size: int # Set maximal size in number of frames. Default is 0.
+  --start (-s): int # Set first frame of loop. Default is 0.
+  --time (-t): float # Set the time of loop start in seconds. Only used if option named start is set to -1.
+] {
+  complex-filter loop {
+    loop: $loop
+    size: $size
+    start: (if ($time | is-empty) { $start } else { -1 })
+    time: $time
+  }
+}
diff --git a/filters_test.nu b/filters_test.nu
new file mode 100644
index 0000000..34346cd
--- /dev/null
+++ b/filters_test.nu
@@ -0,0 +1,25 @@
+#!/usr/bin/env nu
+
+use std [assert];
+
+use ./filters.nu [complex-filter loop "parse filter"];
+
+#[test]
+def loop_has_defaults [] {
+  let got = (loop 10 1);
+  let want = (complex-filter 'loop' { loop: 10 size: 1 });
+  assert equal $got $want;
+}
+
+#[test]
+def setting_time_sets_start_to-1 [] {
+  let got = (loop 10 1 -t 0.5);
+  let want = (complex-filter 'loop' {
+      loop: 10
+      size: 1
+      start: -1
+      time: 0.5
+    });
+
+  assert equal $got $want;
+}