[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/bitio/read.go

@@ -0,0 +1,97 @@
+package bitio
+
+import "io"
+
+type Reader interface {
+	io.Reader
+
+	// alignment:
+	//  |-1-byte-block-|--------------|--------------|--------------|
+	//  |<-offset->|<-------------------width---------------------->|
+	ReadBits(width uint) (data []byte, err error)
+
+	ReadBit() (bit bool, err error)
+}
+
+type ReadSeeker interface {
+	Reader
+	io.Seeker
+}
+
+type reader struct {
+	reader io.Reader
+	octet  byte
+	width  uint
+}
+
+func NewReader(r io.Reader) Reader {
+	return &reader{reader: r}
+}
+
+func (r *reader) Read(p []byte) (n int, err error) {
+	if r.width != 0 {
+		return 0, ErrInvalidAlignment
+	}
+	return r.reader.Read(p)
+}
+
+func (r *reader) ReadBits(size uint) ([]byte, error) {
+	bytes := (size + 7) / 8
+	data := make([]byte, bytes)
+	offset := (bytes * 8) - (size)
+
+	for i := uint(0); i < size; i++ {
+		bit, err := r.ReadBit()
+		if err != nil {
+			return nil, err
+		}
+
+		byteIdx := (offset + i) / 8
+		bitIdx := 7 - (offset+i)%8
+		if bit {
+			data[byteIdx] |= 0x1 << bitIdx
+		}
+	}
+
+	return data, nil
+}
+
+func (r *reader) ReadBit() (bool, error) {
+	if r.width == 0 {
+		buf := make([]byte, 1)
+		if n, err := r.reader.Read(buf); err != nil {
+			return false, err
+		} else if n != 1 {
+			return false, ErrDiscouragedReader
+		}
+		r.octet = buf[0]
+		r.width = 8
+	}
+
+	r.width--
+	return (r.octet>>r.width)&0x01 != 0, nil
+}
+
+type readSeeker struct {
+	reader
+	seeker io.Seeker
+}
+
+func NewReadSeeker(r io.ReadSeeker) ReadSeeker {
+	return &readSeeker{
+		reader: reader{reader: r},
+		seeker: r,
+	}
+}
+
+func (r *readSeeker) Seek(offset int64, whence int) (int64, error) {
+	if whence == io.SeekCurrent && r.reader.width != 0 {
+		return 0, ErrInvalidAlignment
+	}
+	n, err := r.seeker.Seek(offset, whence)
+	if err != nil {
+		return n, err
+	}
+	r.reader.width = 0
+	return n, nil
+}