[feature] Enable basic video support (mp4 only) (#1274)

* [feature] basic video support

* fix missing semicolon

* replace text shadow with stacked icons

Co-authored-by: f0x <f0x@cthu.lu>

vendor/github.com/abema/go-mp4/field.go

@@ -0,0 +1,290 @@
+package mp4
+
+import (
+	"fmt"
+	"os"
+	"reflect"
+	"sort"
+	"strconv"
+	"strings"
+)
+
+type (
+	stringType uint8
+	fieldFlag  uint16
+)
+
+const (
+	stringType_C stringType = iota
+	stringType_C_P
+
+	fieldString        fieldFlag = 1 << iota // 0
+	fieldExtend                              // 1
+	fieldDec                                 // 2
+	fieldHex                                 // 3
+	fieldISO639_2                            // 4
+	fieldUUID                                // 5
+	fieldHidden                              // 6
+	fieldOptDynamic                          // 7
+	fieldVarint                              // 8
+	fieldSizeDynamic                         // 9
+	fieldLengthDynamic                       // 10
+)
+
+type field struct {
+	children []*field
+	name     string
+	cnst     string
+	order    int
+	optFlag  uint32
+	nOptFlag uint32
+	size     uint
+	length   uint
+	flags    fieldFlag
+	strType  stringType
+	version  uint8
+	nVersion uint8
+}
+
+func (f *field) set(flag fieldFlag) {
+	f.flags |= flag
+}
+
+func (f *field) is(flag fieldFlag) bool {
+	return f.flags&flag != 0
+}
+
+func buildFields(box IImmutableBox) []*field {
+	t := reflect.TypeOf(box).Elem()
+	return buildFieldsStruct(t)
+}
+
+func buildFieldsStruct(t reflect.Type) []*field {
+	fs := make([]*field, 0, 8)
+	for i := 0; i < t.NumField(); i++ {
+		ft := t.Field(i).Type
+		tag, ok := t.Field(i).Tag.Lookup("mp4")
+		if !ok {
+			continue
+		}
+		f := buildField(t.Field(i).Name, tag)
+		f.children = buildFieldsAny(ft)
+		fs = append(fs, f)
+	}
+	sort.SliceStable(fs, func(i, j int) bool {
+		return fs[i].order < fs[j].order
+	})
+	return fs
+}
+
+func buildFieldsAny(t reflect.Type) []*field {
+	switch t.Kind() {
+	case reflect.Struct:
+		return buildFieldsStruct(t)
+	case reflect.Ptr, reflect.Array, reflect.Slice:
+		return buildFieldsAny(t.Elem())
+	default:
+		return nil
+	}
+}
+
+func buildField(fieldName string, tag string) *field {
+	f := &field{
+		name: fieldName,
+	}
+	tagMap := parseFieldTag(tag)
+	for key, val := range tagMap {
+		if val != "" {
+			continue
+		}
+		if order, err := strconv.Atoi(key); err == nil {
+			f.order = order
+			break
+		}
+	}
+
+	if val, contained := tagMap["string"]; contained {
+		f.set(fieldString)
+		if val == "c_p" {
+			f.strType = stringType_C_P
+			fmt.Fprint(os.Stderr, "go-mp4: string=c_p tag is deprecated!! See https://github.com/abema/go-mp4/issues/76\n")
+		}
+	}
+
+	if _, contained := tagMap["varint"]; contained {
+		f.set(fieldVarint)
+	}
+
+	if val, contained := tagMap["opt"]; contained {
+		if val == "dynamic" {
+			f.set(fieldOptDynamic)
+		} else {
+			base := 10
+			if strings.HasPrefix(val, "0x") {
+				val = val[2:]
+				base = 16
+			}
+			opt, err := strconv.ParseUint(val, base, 32)
+			if err != nil {
+				panic(err)
+			}
+			f.optFlag = uint32(opt)
+		}
+	}
+
+	if val, contained := tagMap["nopt"]; contained {
+		base := 10
+		if strings.HasPrefix(val, "0x") {
+			val = val[2:]
+			base = 16
+		}
+		nopt, err := strconv.ParseUint(val, base, 32)
+		if err != nil {
+			panic(err)
+		}
+		f.nOptFlag = uint32(nopt)
+	}
+
+	if _, contained := tagMap["extend"]; contained {
+		f.set(fieldExtend)
+	}
+
+	if _, contained := tagMap["dec"]; contained {
+		f.set(fieldDec)
+	}
+
+	if _, contained := tagMap["hex"]; contained {
+		f.set(fieldHex)
+	}
+
+	if _, contained := tagMap["iso639-2"]; contained {
+		f.set(fieldISO639_2)
+	}
+
+	if _, contained := tagMap["uuid"]; contained {
+		f.set(fieldUUID)
+	}
+
+	if _, contained := tagMap["hidden"]; contained {
+		f.set(fieldHidden)
+	}
+
+	if val, contained := tagMap["const"]; contained {
+		f.cnst = val
+	}
+
+	f.version = anyVersion
+	if val, contained := tagMap["ver"]; contained {
+		ver, err := strconv.Atoi(val)
+		if err != nil {
+			panic(err)
+		}
+		f.version = uint8(ver)
+	}
+
+	f.nVersion = anyVersion
+	if val, contained := tagMap["nver"]; contained {
+		ver, err := strconv.Atoi(val)
+		if err != nil {
+			panic(err)
+		}
+		f.nVersion = uint8(ver)
+	}
+
+	if val, contained := tagMap["size"]; contained {
+		if val == "dynamic" {
+			f.set(fieldSizeDynamic)
+		} else {
+			size, err := strconv.ParseUint(val, 10, 32)
+			if err != nil {
+				panic(err)
+			}
+			f.size = uint(size)
+		}
+	}
+
+	f.length = LengthUnlimited
+	if val, contained := tagMap["len"]; contained {
+		if val == "dynamic" {
+			f.set(fieldLengthDynamic)
+		} else {
+			l, err := strconv.ParseUint(val, 10, 32)
+			if err != nil {
+				panic(err)
+			}
+			f.length = uint(l)
+		}
+	}
+
+	return f
+}
+
+func parseFieldTag(str string) map[string]string {
+	tag := make(map[string]string, 8)
+
+	list := strings.Split(str, ",")
+	for _, e := range list {
+		kv := strings.SplitN(e, "=", 2)
+		if len(kv) == 2 {
+			tag[strings.Trim(kv[0], " ")] = strings.Trim(kv[1], " ")
+		} else {
+			tag[strings.Trim(kv[0], " ")] = ""
+		}
+	}
+
+	return tag
+}
+
+type fieldInstance struct {
+	field
+	cfo ICustomFieldObject
+}
+
+func resolveFieldInstance(f *field, box IImmutableBox, parent reflect.Value, ctx Context) *fieldInstance {
+	fi := fieldInstance{
+		field: *f,
+	}
+
+	cfo, ok := parent.Addr().Interface().(ICustomFieldObject)
+	if ok {
+		fi.cfo = cfo
+	} else {
+		fi.cfo = box
+	}
+
+	if fi.is(fieldSizeDynamic) {
+		fi.size = fi.cfo.GetFieldSize(f.name, ctx)
+	}
+
+	if fi.is(fieldLengthDynamic) {
+		fi.length = fi.cfo.GetFieldLength(f.name, ctx)
+	}
+
+	return &fi
+}
+
+func isTargetField(box IImmutableBox, fi *fieldInstance, ctx Context) bool {
+	if box.GetVersion() != anyVersion {
+		if fi.version != anyVersion && box.GetVersion() != fi.version {
+			return false
+		}
+
+		if fi.nVersion != anyVersion && box.GetVersion() == fi.nVersion {
+			return false
+		}
+	}
+
+	if fi.optFlag != 0 && box.GetFlags()&fi.optFlag == 0 {
+		return false
+	}
+
+	if fi.nOptFlag != 0 && box.GetFlags()&fi.nOptFlag != 0 {
+		return false
+	}
+
+	if fi.is(fieldOptDynamic) && !fi.cfo.IsOptFieldEnabled(fi.name, ctx) {
+		return false
+	}
+
+	return true
+}