rtpdec_jpeg: compute Q tables for 0-127

code taken directly from RFC 2435 text

src/rtp/rtpdec_jpeg.c

@@ -4,9 +4,7 @@
  * @author Martin Pulec     <[email protected]>
  *
  * @todo
- * * handle predefined (0-127) quantization tables
  * * handle precision=1 (?)
- * * error meesage for zero-len quantization tables
  */
 /*
  * Copyright (c) 2024 CESNET
@@ -191,6 +189,65 @@ skip_jpeg_headers(unsigned char **pckt_data)
         }
 }
 
+/*
+ * Table K.1 from JPEG spec.
+ */
+static const int jpeg_luma_quantizer[64] = {
+        16, 11, 10, 16, 24, 40, 51, 61,
+        12, 12, 14, 19, 26, 58, 60, 55,
+        14, 13, 16, 24, 40, 57, 69, 56,
+        14, 17, 22, 29, 51, 87, 80, 62,
+        18, 22, 37, 56, 68, 109, 103, 77,
+        24, 35, 55, 64, 81, 104, 113, 92,
+        49, 64, 78, 87, 103, 121, 120, 101,
+        72, 92, 95, 98, 112, 100, 103, 99
+};
+
+/*
+ * Table K.2 from JPEG spec.
+ */
+static const int jpeg_chroma_quantizer[64] = {
+        17, 18, 24, 47, 99, 99, 99, 99,
+        18, 21, 26, 66, 99, 99, 99, 99,
+        24, 26, 56, 99, 99, 99, 99, 99,
+        47, 66, 99, 99, 99, 99, 99, 99,
+        99, 99, 99, 99, 99, 99, 99, 99,
+        99, 99, 99, 99, 99, 99, 99, 99,
+        99, 99, 99, 99, 99, 99, 99, 99,
+        99, 99, 99, 99, 99, 99, 99, 99
+};
+
+/*
+ * Call MakeTables with the Q factor and two u_char[64] return arrays
+ */
+static void
+MakeTables(int q, u_char *lqt, u_char *cqt)
+{
+  int i;
+  int factor = q;
+
+  if (q < 1) factor = 1;
+  if (q > 99) factor = 99;
+  if (q < 50)
+    q = 5000 / factor;
+  else
+    q = 200 - factor*2;
+
+  for (i=0; i < 64; i++) {
+    int lq = (jpeg_luma_quantizer[i] * q + 50) / 100;
+    int cq = (jpeg_chroma_quantizer[i] * q + 50) / 100;
+
+    /* Limit the quantizers to 1 <= q <= 255 */
+    if (lq < 1) lq = 1;
+    else if (lq > 255) lq = 255;
+    lqt[i] = lq;
+
+    if (cq < 1) cq = 1;
+    else if (cq > 255) cq = 255;
+    cqt[i] = cq;
+  }
+}
+
 int
 decode_frame_jpeg(struct coded_data *cdata, void *decode_data)
 {
@@ -236,6 +293,13 @@ decode_frame_jpeg(struct coded_data *cdata, void *decode_data)
                 cdata = cdata->nxt;
         }
 
+        if (!dec_data->jpeg.quantization_table_set[q] &&
+            q < QUANT_TAB_T_FIRST_STATIC) {
+                MakeTables(q, dec_data->jpeg.quantization_tables[q][0],
+                           dec_data->jpeg.quantization_tables[q][1]);
+                dec_data->jpeg.quantization_table_set[q] = true;
+        }
+
         if (!dec_data->jpeg.quantization_table_set[q]) {
                 MSG(WARNING,
                     "Dropping frame - missing quantization tables for Q=%d!\n",