[mp4tree] Break out NAL and SEI parsing

  * A refactoring step since main file has grown a bit

Makefile

@@ -4,6 +4,9 @@ TARGET = mp4tree
 
 SRCS := mp4tree.c
 SRCS += atom-desc.c
+SRCS += common.c
+SRCS += nal.c
+SRCS += sei.c
 
 $(TARGET): $(SRCS)
 	$(CC) $(CFLAGS) -o $(TARGET) $(SRCS)

common.c

@@ -0,0 +1,26 @@
+#include <string.h>
+
+#include "common.h"
+
+const char *
+indent(int depth, int header)
+{
+    static char buf[64];
+    int i = 0;
+
+    memset(buf, 0 , sizeof buf);
+
+    for (i = 0; i < depth; i++)
+    {
+        strcat(buf, "|  ");
+    }
+
+    if (header)
+        strcat(buf, "+");
+    else
+        strcat(buf, "");
+
+    return buf;
+}
+
+

common.h

@@ -0,0 +1,7 @@
+#pragma once
+
+#include <stdlib.h>
+#include <stdint.h>
+
+const char *
+indent(int depth, int header);