[feature] For video attachments, store + return fps, bitrate, duration (#1282)

* start messing about with different mp4 metadata extraction

* heyyooo it works

* add test cow

* move useful multierror to gtserror package

* error out if video doesn't seem to be a real mp4

* test parsing mkv in disguise as mp4

* tidy up error handling

* remove extraneous line

* update framerate formatting

* use float32 for aspect

* fixy mctesterson

internal/gtserror/multi.go

@@ -0,0 +1,45 @@
+/*
+   GoToSocial
+   Copyright (C) 2021-2022 GoToSocial Authors admin@gotosocial.org
+
+   This program is free software: you can redistribute it and/or modify
+   it under the terms of the GNU Affero General Public License as published by
+   the Free Software Foundation, either version 3 of the License, or
+   (at your option) any later version.
+
+   This program is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+   GNU Affero General Public License for more details.
+
+   You should have received a copy of the GNU Affero General Public License
+   along with this program.  If not, see <http://www.gnu.org/licenses/>.
+*/
+
+package gtserror
+
+import (
+	"errors"
+	"fmt"
+	"strings"
+)
+
+// MultiError allows encapsulating multiple errors under a singular instance,
+// which is useful when you only want to log on errors, not return early / bubble up.
+type MultiError []string
+
+func (e *MultiError) Append(err error) {
+	*e = append(*e, err.Error())
+}
+
+func (e *MultiError) Appendf(format string, args ...any) {
+	*e = append(*e, fmt.Sprintf(format, args...))
+}
+
+// Combine converts this multiError to a singular error instance, returning nil if empty.
+func (e MultiError) Combine() error {
+	if len(e) == 0 {
+		return nil
+	}
+	return errors.New(`"` + strings.Join(e, `","`) + `"`)
+}