func (list FormatList) Quality(quality string) (result FormatList) {
	for _, f := range list {
		itag, _ := strconv.Atoi(quality)
		if itag == f.ItagNo || strings.Contains(f.Quality, quality) || strings.Contains(f.QualityLabel, quality) {
			result = append(result, f)
		}
	}
	return result
}
Quality returns a new FormatList filtered by quality, quality label or itag,
but not audio quality
package youtube
import (
	"sort"
	"strconv"
	"strings"
)
type FormatList []Format
func (list FormatList) FindByQuality(quality string) *Format {
	for i := range list {
		if list[i].Quality == quality || list[i].QualityLabel == quality {
			return &list[i]
		}
	}
	return nil
}
func (list FormatList) FindByItag(itagNo int) *Format {
	for i := range list {
		if list[i].ItagNo == itagNo {
			return &list[i]
		}
	}
	return nil
}
func (list FormatList) Type(t string) (result FormatList) {
	for i := range list {
		if strings.Contains(list[i].MimeType, t) {
			result = append(result, list[i])
		}
	}
	return result
}