If you have jq installed (
https://jqlang.github.io/jq/) somewhere where you have curl, you can easily filter any API response to find files whose filename contains m4v, for example, you can get recent posts with videos with:
curl -X 'GET' '
https://coomer.su/api/v1/posts' -H 'accept: application/json' | jq '.[] | select( [ .file.name | contains("m4v") ] | any ), select( [ .attachments[].name | contains("m4v") ] | any ) | "
https://coomer.su/" + .service + "/user/" + .user + "/post/" + .id'