Fix HRD buffering entry count and following field alignment

README.md

@@ -92,7 +92,9 @@ v -cc msvc test .
 
 They cover fixed-width and Exp-Golomb bit reading, truncated input behavior,
 NAL headers, RBSP look-ahead, integer bit widths, and representative
-High-profile SPS/PPS parsing used by the player.
+High-profile SPS/PPS parsing used by the player. HRD buffering syntax tests cover
+one, two, and the maximum 32 CPB entries, including alignment of the following
+delay fields. Counts beyond 32 entries are rejected by an assertion.
 
 CI also runs strict V3 with TinyCC on Linux, using a pinned compiler snapshot.
 The regression samples cover custom SPS/PPS scaling lists and the default-list

h264.v

@@ -412,11 +412,13 @@ pub fn (mut b Bitstream) read_scaling_list(mut scaling_list []i32, size_of_scali
 
 // read_hrd_parameters consumes HRD syntax at the current cursor into sps.hrd.
 // Normally called by read_vui_parameters; it does not schedule decoder buffering.
+// The coded count is one less than the number of entries and must be at most 31.
 pub fn (mut sps SequenceParameterSet) read_hrd_parameters(mut b Bitstream) {
 	sps.hrd.cpb_cnt_minus1 = b.ue()
+	assert sps.hrd.cpb_cnt_minus1 < 32
 	sps.hrd.bit_rate_scale = b.u(4)
 	sps.hrd.cpb_size_scale = b.u(4)
-	for sched_sel_idx in 0 .. sps.hrd.cpb_cnt_minus1 {
+	for sched_sel_idx in 0 .. sps.hrd.cpb_cnt_minus1 + 1 {
 		sps.hrd.bit_rate_value_minus1[sched_sel_idx] = b.ue()
 		sps.hrd.cpb_size_value_minus1[sched_sel_idx] = b.ue()
 		sps.hrd.cbr_flag[sched_sel_idx] = b.u1()

hrd_test.v

@@ -0,0 +1,32 @@
+// Verifies HRD entry counts and the cursor position of following syntax fields.
+module h264
+
+import encoding.hex
+
+fn test_hrd_reads_all_cpb_entries() {
+	// H.264 E.1.2 encodes count minus one. Fixtures contain 1, 2 and 32 CPBs,
+	// distinct entry values, four delay widths, and an 0xa5 cursor sentinel.
+	for count, encoded in {
+		1:  '9a30208a63a294'
+		2:  '468c08220102531d14a0'
+		32: '04068c08220102507e303e9c1e8403c89076140ea2c1c860388d06e1c0da3c1a8200d2110660903284c188280c21505e0b02e85c168300b2190560d02a86c148380a21d04e0f02687c1281002482104604408a531d14a0'
+	} {
+		mut stream := Bitstream{}
+		stream.init(hex.decode(encoded)!)
+		mut sps := SequenceParameterSet{}
+		sps.read_hrd_parameters(mut stream)
+		assert sps.hrd.cpb_cnt_minus1 == u32(count - 1)
+		assert sps.hrd.bit_rate_scale == 3
+		assert sps.hrd.cpb_size_scale == 4
+		for i in 0 .. count {
+			assert sps.hrd.bit_rate_value_minus1[i] == u32(i + 2)
+			assert sps.hrd.cpb_size_value_minus1[i] == u32(64 - i)
+			assert sps.hrd.cbr_flag[i] == u32(i % 2)
+		}
+		assert sps.hrd.initial_cpb_removal_delay_length_minus1 == 5
+		assert sps.hrd.cpb_removal_delay_length_minus1 == 6
+		assert sps.hrd.dpb_output_delay_length_minus1 == 7
+		assert sps.hrd.time_offset_length == 8
+		assert stream.u(8) == 0xa5
+	}
+}