[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/write.go

@@ -0,0 +1,61 @@
+package bitio
+
+import (
+	"io"
+)
+
+type Writer interface {
+	io.Writer
+
+	// alignment:
+	//  |-1-byte-block-|--------------|--------------|--------------|
+	//  |<-offset->|<-------------------width---------------------->|
+	WriteBits(data []byte, width uint) error
+
+	WriteBit(bit bool) error
+}
+
+type writer struct {
+	writer io.Writer
+	octet  byte
+	width  uint
+}
+
+func NewWriter(w io.Writer) Writer {
+	return &writer{writer: w}
+}
+
+func (w *writer) Write(p []byte) (n int, err error) {
+	if w.width != 0 {
+		return 0, ErrInvalidAlignment
+	}
+	return w.writer.Write(p)
+}
+
+func (w *writer) WriteBits(data []byte, width uint) error {
+	length := uint(len(data)) * 8
+	offset := length - width
+	for i := offset; i < length; i++ {
+		oi := i / 8
+		if err := w.WriteBit((data[oi]>>(7-i%8))&0x01 != 0); err != nil {
+			return err
+		}
+	}
+	return nil
+}
+
+func (w *writer) WriteBit(bit bool) error {
+	if bit {
+		w.octet |= 0x1 << (7 - w.width)
+	}
+	w.width++
+
+	if w.width == 8 {
+		if _, err := w.writer.Write([]byte{w.octet}); err != nil {
+			return err
+		}
+		w.octet = 0x00
+		w.width = 0
+	}
+	return nil
+}