From 28bcaf876c196a261e55d7cff7bbf6b274868a21 Mon Sep 17 00:00:00 2001
From: Moritz Bunkus <mo@bunkus.online>
Date: Tue, 6 Jul 2021 09:52:13 +0200
Subject: [PATCH] MPEG 1/2 packetizer: use rationals for calculation of aspect
 ratio

---
 src/common/mpeg1_2.cpp   | 34 ++++++++++++----------------------
 src/common/mpeg1_2.h     |  4 +++-
 src/output/p_mpeg1_2.cpp |  8 ++++----
 3 files changed, 19 insertions(+), 27 deletions(-)

diff --git a/src/common/mpeg1_2.cpp b/src/common/mpeg1_2.cpp
index 12d142c29..eacc50818 100644
--- a/src/common/mpeg1_2.cpp
+++ b/src/common/mpeg1_2.cpp
@@ -75,17 +75,16 @@ extract_fps_idx(unsigned char const *buffer,
 
    \return \c true if a MPEG sequence header was found and \c false otherwise.
 */
-bool
-extract_ar(unsigned char const *buffer,
-           int buffer_size,
-           double &ar) {
+std::optional<mtx_mp_rational_t>
+extract_aspect_ratio(unsigned char const *buffer,
+                     int buffer_size) {
   uint32_t marker;
   int idx;
 
   mxdebug_if(s_debug, fmt::format("mpeg_video_ar: start search in {0} bytes\n", buffer_size));
   if (buffer_size < 8) {
     mxdebug_if(s_debug, "mpeg_video_ar: sequence header too small\n");
-    return false;
+    return {};
   }
   marker = get_uint32_be(buffer);
   idx = 4;
@@ -96,33 +95,24 @@ extract_ar(unsigned char const *buffer,
   }
   if (idx >= buffer_size) {
     mxdebug_if(s_debug, "mpeg_video_ar: no sequence header start code found\n");
-    return false;
+    return {};
   }
 
   mxdebug_if(s_debug, fmt::format("mpeg_video_ar: found sequence header start code at {0}\n", idx - 4));
   idx += 3;                     // width and height
   if (idx >= buffer_size) {
     mxdebug_if(s_debug, "mpeg_video_ar: sequence header too small\n");
-    return false;
+    return {};
   }
 
   switch (buffer[idx] & 0xf0) {
-    case AR_1_1:
-      ar = 1.0;
-      break;
-    case AR_4_3:
-      ar = 4.0 / 3.0;
-      break;
-    case AR_16_9:
-      ar = 16.0 / 9.0;
-      break;
-    case AR_2_21:
-      ar = 2.21;
-      break;
-    default:
-      ar = -1.0;
+    case AR_1_1:  return mtx::rational(1, 1);
+    case AR_4_3:  return mtx::rational(4, 3);
+    case AR_16_9: return mtx::rational(16, 9);
+    case AR_2_21: return mtx::rational(221, 100);
   }
-  return true;
+
+  return {};
 }
 
 /** \brief Get the number of frames per second
diff --git a/src/common/mpeg1_2.h b/src/common/mpeg1_2.h
index 298e76cf9..3fd97eba5 100644
--- a/src/common/mpeg1_2.h
+++ b/src/common/mpeg1_2.h
@@ -16,6 +16,8 @@
 
 #include "common/common_pch.h"
 
+#include "common/math_fwd.h"
+
 namespace mtx::mpeg1_2 {
 
 // MPEG-1/-2 video start codes
@@ -65,7 +67,7 @@ constexpr auto FOURCC_MPEG2                  = 0x10000002u;
 
 int extract_fps_idx(const unsigned char *buffer, int buffer_size);
 double get_fps(int idx);
-bool extract_ar(const unsigned char *buffer, int buffer_size, double &ar);
+std::optional<mtx_mp_rational_t> extract_aspect_ratio(const unsigned char *buffer, int buffer_size);
 bool is_fourcc(uint32_t fourcc);
 
 }
diff --git a/src/output/p_mpeg1_2.cpp b/src/output/p_mpeg1_2.cpp
index be1b9a53d..8b6de855b 100644
--- a/src/output/p_mpeg1_2.cpp
+++ b/src/output/p_mpeg1_2.cpp
@@ -271,15 +271,15 @@ mpeg1_2_video_packetizer_c::extract_fps(const unsigned char *buffer,
 void
 mpeg1_2_video_packetizer_c::extract_aspect_ratio(const unsigned char *buffer,
                                                  int size) {
-  double ar;
-
   if (display_dimensions_or_aspect_ratio_set())
     return;
 
-  if (!mtx::mpeg1_2::extract_ar(buffer, size, ar))
+  auto aspect_ratio = mtx::mpeg1_2::extract_aspect_ratio(buffer, size);
+
+  if (!aspect_ratio)
     return;
 
-  set_video_display_dimensions((0 >= ar) || (1 == ar) ? m_width : (int)(m_height * ar), m_height, generic_packetizer_c::ddu_pixels, OPTION_SOURCE_BITSTREAM);
+  set_video_display_dimensions(1 == *aspect_ratio ? m_width : mtx::to_int(m_height * *aspect_ratio), m_height, generic_packetizer_c::ddu_pixels, OPTION_SOURCE_BITSTREAM);
 
   rerender_track_headers();
   m_aspect_ratio_extracted = true;