Merge pull request #118 from jrdennisoss/issue-117

Drive "magic" MPEG video correction from "magic keys" provided by the emulated game.

NOTES_MPEG.md

@@ -50,20 +50,23 @@ Facts:
 
 * Can the `f_code` update per picture as with standard MPEG-1 video, or is it limited to one static forward/backward static value pair per MPEG file/sequence?
 * What is the exact relationship between temporal sequence number and `f_code`?
+* How exactly does the `driver_call(9, X, 0208h, ...)` (aka. "Magic Key") call directly impact this?
 
 ## Current Emulator Workaround
 
-A truthful `f_code` value appears to be in all P and B pictures with a temporal
-sequence number of either 3 or 8, so I am currently seeking to the first P or B 
-picture header matching these criteria, and applying a static `f_code`
-value to all forward and backward motion vector `f_code` values for
-magical MPEG files.
-
-For picture headers containing empty "user data", I use 4 as the truthful
-temporal sequence number. (The Horde)
+The emulator takes uses `driver_call(9, X, 0208h, ...)` (aka "Set Magic Key") to determine where to find a
+truthful `f_code` value which gets applied to the entire MPEG asset when a "magical" `picture_rate` code
+is specified. The MPEG asset file is quickly scrubbed at media handle open time to find a matchiing P or B
+picture containing a truthful `f_code` value. Then this value is statically applied to the entire decoding
+of said MPEG asset file.
 
 Eventually, I think this needs to be handled on a per-picture basis.
 
+Known "magic key" values:
+
+* 0x40044041 -- Default value. Truthful `f_code` found in temporal sequence number of 3 or 8.
+* 0xC39D7088 -- Used in The Horde. Truthful `f_code` found in temporal sequence number of 4.
+
 
 ## Analyzing and Inspecting These Files
 

README.md

@@ -81,12 +81,13 @@ configure anything to have a working ReelMagic setup as the defaults will
 enable ReelMagic emulation.
 The parameters are:
 
-* `enabled`        -- Enables/disables the ReelMagic emulator. By default this is `true`
-* `alwaysresident` -- This forces `FMPDRV.EXE` to always be loaded.  By default this is `false`
-* `vgadup5hack`    -- Duplicate every 5th VGA line to help give output a 4:3 ratio. By default this is `false`
-* `magicfhack`     -- Use for MPEG video debugging purposes only. See `reelmagic_player.cpp` for what exactly this does to the MPEG decoder.
-* `a204debug`      -- Controls FMPDRV.EXE function Ah subfunction 204h debug logging. Only applicable in "heavy debugging" build.
-* `a206debug`      -- Controls FMPDRV.EXE function Ah subfunction 206h debug logging. Only applicable in "heavy debugging" build.
+* `enabled`         -- Enables/disables the ReelMagic emulator. By default this is `true`
+* `alwaysresident`  -- This forces `FMPDRV.EXE` to always be loaded.  By default this is `false`
+* `vgadup5hack`     -- Duplicate every 5th VGA line to help give output a 4:3 ratio. By default this is `false`
+* `initialmagickey` -- Provides and alternate value for the initial global "magic key" value in hex. Defaults to 40044041.
+* `magicfhack`      -- Use for MPEG video debugging purposes only. See `reelmagic_player.cpp` for what exactly this does to the MPEG decoder.
+* `a204debug`       -- Controls FMPDRV.EXE function Ah subfunction 204h debug logging. Only applicable in "heavy debugging" build.
+* `a206debug`       -- Controls FMPDRV.EXE function Ah subfunction 206h debug logging. Only applicable in "heavy debugging" build.
 
 
 For example:

dosbox-0.74-3/src/dosbox.cpp

@@ -661,12 +661,14 @@ void DOSBOX_Init(void) {
 	Pbool->Set_help("Force the FMPDRV.EXE to always be resident and not unloadable.");
 	Pbool = secprop->Add_bool("vgadup5hack",Property::Changeable::OnlyAtStart,false);
 	Pbool->Set_help("Enable the VGA DUP5 Hack. Duplicate's every VGA 5th line.");
-    Pint = secprop->Add_int("audiolevel", Property::Changeable::OnlyAtStart,150);
+	Pint = secprop->Add_int("audiolevel", Property::Changeable::OnlyAtStart,150);
 	Pint->Set_help("Sets the MPEG audio sample level in percents. Defaults to 150%");
-    Pint = secprop->Add_int("audiofifosize", Property::Changeable::OnlyAtStart,30);
+	Pint = secprop->Add_int("audiofifosize", Property::Changeable::OnlyAtStart,30);
 	Pint->Set_help("Sets the MPEG audio frame FIFO size. Defaults to 30 MPEG audio frames.");
-    Pint = secprop->Add_int("audiofifodispose", Property::Changeable::OnlyAtStart,2);
+	Pint = secprop->Add_int("audiofifodispose", Property::Changeable::OnlyAtStart,2);
 	Pint->Set_help("Sets the count of MPEG audio frames to dispose of when the MPEG is going faster than audio-side of things and the FIFO hits max. Defaults to 2.");
+	Pstring = secprop->Add_string("initialmagickey",Property::Changeable::OnlyAtStart,"40044041");
+	Pstring->Set_help("Provides and alternate value for the initial global \"magic key\" value in hex. Defaults to 40044041.");
 	Pint = secprop->Add_int("magicfhack",Property::Changeable::OnlyAtStart,0);
 	Pint->Set_help("MPEG debugging only! Consult the reelmagic_player.cpp source code and NOTES_MPEG.md");
 	Pbool = secprop->Add_bool("a204debug",Property::Changeable::OnlyAtStart,true);

dosbox-0.74-3/src/hardware/reelmagic_player.cpp

@@ -39,11 +39,12 @@
 #include "./reelmagic_pl_mpeg.h"
 
 //global config
-static int _magicalFcodeOverride = 0; //0 = no override
 static ReelMagic_PlayerConfiguration _globalDefaultPlayerConfiguration;
 static double _audioLevel = 1.5;
 static Bitu _audioFifoSize = 30;
 static Bitu _audioFifoDispose = 2;
+static Bitu _initialMagicKey = 0x40044041;
+static int _magicalFcodeOverride = 0; //0 = no override
 
 
 
@@ -259,13 +260,13 @@ namespace { class ReelMagic_MediaPlayerImplementation : public ReelMagic_MediaPl
     //the idea here is that MPEG-1 assets with a picture_rate code >= 0x9 in the MPEG sequence
     //header have screwed up f_code values. i'm not sure why but this may be some form of copy
     //and/or clone protection for ReelMagic. pictures with a temporal sequence number of either
-    //3 or 8 seem to contain a truthful f_code for Return to Zork and Lord of the Rings assets
-    //4 seems to contain the truthful f_code for The Horde. The Horde also has an empty user
-    //data chunk in the picture header too which is used to identify this.
+    //3 or 8 seem to contain a truthful f_code when a "key" of 0x40044041 (ReelMagic default)
+    //is given to us and a temporal sequence number of 4 seems to contain the truthful f_code
+    //when a "key" of 0xC39D7088 is given to us
     //
     //for now, this hack scrubs the MPEG file in search of the first P or B pictures with a
-    //temporal sequence number of 3 or 8 (or 4 for The Horde / user data) and returns the
-    //f_code value. then the player applies the f_code as a global static forward and
+    //temporal sequence number matching a truthful value based on the player's "magic key"
+    //the player then applies the found f_code value as a global static forward and
     //backward value for this entire asset.
     //
     //ultimately, this should probably be done on a per-picture basis using some sort of
@@ -289,13 +290,18 @@ namespace { class ReelMagic_MediaPlayerImplementation : public ReelMagic_MediaPl
         plm_buffer_skip(_plm->video_decoder->buffer, 16); // skip vbv_delay
         plm_buffer_skip(_plm->video_decoder->buffer, 1); //skip full_px
         result = plm_buffer_read(_plm->video_decoder->buffer, 3);
-        if (plm_buffer_next_start_code(_plm->video_decoder->buffer) == PLM_START_USER_DATA) {
-          // The Horde videos tsn=4 is truthful
+        switch (_config.MagicDecodeKey) {
+        case 0xC39D7088: //The Horde uses this "key"
           if (temporal_seqnum != 4) result = 0;
-        }
-        else {
-          // Return to Zork and Lord of the Rings videos tsn=3 and tns=8 is truthful
+          break;
+
+        default:
+          LOG(LOG_REELMAGIC, LOG_WARN)("Unknown magic key 0x%08X. Defaulting to 0x40044041", (unsigned)_config.MagicDecodeKey);
+          //fall-through
+        case 0x40044041: //most ReelMagic games seem to use this "key"
+          //tsn=3 and tsn=8 seem to contain truthful 
           if ((temporal_seqnum != 3) && (temporal_seqnum != 8)) result = 0;
+          break;
         }
       }
     } while (result == 0);
@@ -700,6 +706,11 @@ void ReelMagic_InitPlayer(Section* sec) {
   _audioFifoSize = section->Get_int("audiofifosize");
   _audioFifoDispose = section->Get_int("audiofifodispose");
 
+  //read in the initial global magic key from configuration
+  unsigned long scanval;
+  if (sscanf(section->Get_string("initialmagickey"), "%lX", &scanval) != 1) scanval = 0x40044041;
+  _initialMagicKey = scanval;
+
   //XXX Remove this as it is ONLY for debugging MPEG assets!!!
   _magicalFcodeOverride = section->Get_int("magicfhack");
   if ((_magicalFcodeOverride < 0) || (_magicalFcodeOverride > 7))
@@ -716,7 +727,7 @@ void ReelMagic_ResetPlayers() {
   cfg.VideoOutputVisible = true;
   cfg.UnderVga = false;
   cfg.VgaAlphaIndex = 0;
-  cfg.MagicDecodeKey = 0x40044041;
+  cfg.MagicDecodeKey = _initialMagicKey;
   cfg.DisplayPosition.X = 0;
   cfg.DisplayPosition.Y = 0;
   cfg.DisplaySize.Width = 0;

example.dosbox.conf

@@ -266,6 +266,8 @@ alwaysresident=true
 #audiolevel=150
 #audiofifosize=30
 #audiofifodispose=2
+#initialmagickey=40044041
+#initialmagickey=C39D7088
 #a204debug=false
 #a206debug=false