media: Format description struct, stubs for more formats

packages/media/src/qoa.zig

@@ -1,8 +1,27 @@
 const std = @import("std");
 
+const Format = @import("Format.zig");
+
+const format: Format = .{
+    .magic_length = magic.len,
+    // 4B - sample count
+    // 1B - channels
+    // 3B - sample rate
+    .info_length = magic.len + 8,
+    .extension = "qoa",
+    .media_type = "audio/qoa",
+    .isFormat = isQoa,
+};
+
+const magic = "qoaf";
+
 const Header = union(enum) {
     streaming: HeaderStreaming,
     static: HeaderStatic,
+
+    pub fn initStatic(static: HeaderStatic) Header {
+        return .{ .static = static };
+    }
 };
 
 const HeaderStreaming = void;
@@ -19,30 +38,38 @@ const HeaderStatic = struct {
     }
 };
 
-/// The caller asserts that the buffer is at least 12 bytes long, which can
-/// contain the entirety of a QOA file header and the relevant information in
-/// the first frame header.
-pub fn info(buffer: []const u8) ?Header {
-    std.debug.assert(buffer.len >= 12);
+/// The caller asserts that the buffer is at least `format.magic_length` bytes
+/// long.
+pub fn isQoa(buffer: []const u8) bool {
+    return std.mem.eql(u8, buffer[0..format.magic_length], magic);
+}
+
+/// The caller asserts that the buffer is at least `format.info_length` bytes
+/// long.
+pub fn info(buffer: []const u8) ?Header {
+    std.debug.assert(buffer.len >= format.info_length);
+
+    if (!isQoa(buffer)) {
+        return null;
+    }
 
-    const magic = buffer[0..4];
     const samples = std.mem.readInt(u32, buffer[4..8], .big);
     const channels = buffer[8];
     const sample_rate = std.mem.readInt(u24, buffer[9..12], .big);
 
-    if (!std.mem.eql(u8, magic, "qoaf") or channels == 0 or channels > 8 or sample_rate == 0) {
+    if (channels == 0 or channels > 8 or
+        sample_rate == 0)
+    {
         return null;
     }
 
     if (samples == 0) {
         return .streaming;
     } else {
-        return .{
-            .static = .{
-                .samples = samples,
-                .channels = channels,
-                .sample_rate = sample_rate,
-            },
-        };
+        return .initStatic(.{
+            .samples = samples,
+            .channels = channels,
+            .sample_rate = sample_rate,
+        });
     }
 }