From e84500bb3e5314c47adfaf9c98e73e4113f86a9b Mon Sep 17 00:00:00 2001
From: Sam Lantinga <slouken@libsdl.org>
Date: Mon, 18 Sep 2017 16:05:46 -0700
Subject: [PATCH] Fixed bug 3833 - Silent MP3 playback using included smpeg2
 library

Holger Schemel

Summary: When playing MP3 files using the included smpeg2 library, audio output is silent.

How to reproduce the problem: Build latest SDL2_mixer and smpeg2 (from directory "external/smpeg2-2.0.0") and play MP3 file using included music player "playmus". (Tested on Ubuntu 12.04 and Mac OS X 10.11.)

Expected behaviour: "playmus" plays MP3 music through the computer's audio device.

Observed behaviour: "playmus" appears to be playing, but the computer's audio device remains silent.

The problem was introduced with changeset 718:fb0562cc1559, which replaces legacy functions like SDL_OpenAudio(), SDL_LockAudio(), SDL_PauseAudio(), SDL_MixAudio() etc. with their non-legacy counterparts like SDL_OpenAudioDevice(), SDL_LockAudioDevice(), SDL_PauseAudioDevice() and SDL_MixAudioFormat() in the SDL2_mixer code, while the smpeg2 code still uses the legacy functions.

Replacing SDL_MixAudio() with SDL_MixAudioFormat() in the smpeg2 code fixes the problem, and MP3 playback using SDL2_mixer with smpeg2 works fine again (from both "playmus" and from my SDL2/SDL2_mixer/smpeg2 based games).

The attached patch fixes the problem.
---
 external/smpeg2-2.0.0/MPEGaudio.h         |  1 +
 external/smpeg2-2.0.0/audio/MPEGaudio.cpp |  3 +++
 external/smpeg2-2.0.0/audio/mpegtoraw.cpp | 14 +++++++-------
 3 files changed, 11 insertions(+), 7 deletions(-)

diff --git a/external/smpeg2-2.0.0/MPEGaudio.h b/external/smpeg2-2.0.0/MPEGaudio.h
index 3f315d2a..54c340e1 100644
--- a/external/smpeg2-2.0.0/MPEGaudio.h
+++ b/external/smpeg2-2.0.0/MPEGaudio.h
@@ -186,6 +186,7 @@ class MPEGaudio : public MPEGerror, public MPEGaudioaction {
     double rate_in_s;
     Uint32 frags_playing;
     Uint32 frag_time;
+    SDL_AudioFormat format;
 #ifdef THREADED_AUDIO
     bool decoding;
     SDL_Thread *decode_thread;
diff --git a/external/smpeg2-2.0.0/audio/MPEGaudio.cpp b/external/smpeg2-2.0.0/audio/MPEGaudio.cpp
index 9728d4c9..45c69dc9 100644
--- a/external/smpeg2-2.0.0/audio/MPEGaudio.cpp
+++ b/external/smpeg2-2.0.0/audio/MPEGaudio.cpp
@@ -34,6 +34,7 @@ MPEGaudio:: MPEGaudio(MPEGstream *stream, bool initSDL)
     , rate_in_s(0.0)
     , frags_playing(0)
     , frag_time(0)
+    , format(0)
 #ifdef THREADED_AUDIO
     , decoding(false)
     , decode_thread(NULL)
@@ -155,6 +156,8 @@ MPEGaudio:: ActualSpec(const SDL_AudioSpec *actual)
     }
     rate_in_s=((double)((actual->format&0xFF)/8)*actual->channels*actual->freq);
     stereo=((actual->channels-1) > 0);
+
+    format = actual->format;
 }
 
 #ifdef THREADED_AUDIO
diff --git a/external/smpeg2-2.0.0/audio/mpegtoraw.cpp b/external/smpeg2-2.0.0/audio/mpegtoraw.cpp
index 493c8709..22dcf9fe 100644
--- a/external/smpeg2-2.0.0/audio/mpegtoraw.cpp
+++ b/external/smpeg2-2.0.0/audio/mpegtoraw.cpp
@@ -429,7 +429,7 @@ int Play_MPEGaudio(MPEGaudio *audio, Uint8 *stream, int len)
 	   quite right */
         copylen = audio->ring->NextReadBuffer(&rbuf);
         if ( copylen > len ) {
-            SDL_MixAudio(stream, rbuf, len, volume);
+	    SDL_MixAudioFormat(stream, rbuf, audio->format, len, volume);
             mixed += len;
             audio->ring->ReadSome(len);
             len = 0;
@@ -437,7 +437,7 @@ int Play_MPEGaudio(MPEGaudio *audio, Uint8 *stream, int len)
 		audio->timestamp[i] = audio->timestamp[i+1];
 	    audio->timestamp[N_TIMESTAMPS-1] = audio->ring->ReadTimeStamp();
         } else {
-            SDL_MixAudio(stream, rbuf, copylen, volume);
+	    SDL_MixAudioFormat(stream, rbuf, audio->format, copylen, volume);
             mixed += copylen;
             ++audio->currentframe;
             audio->ring->ReadDone();
@@ -477,14 +477,14 @@ int Play_MPEGaudio(MPEGaudio *audio, Uint8 *stream, int len)
         copylen = (audio->rawdatawriteoffset-audio->rawdatareadoffset);
         assert(copylen >= 0);
         if ( copylen >= len ) {
-            SDL_MixAudio(stream, (Uint8 *)&audio->spillover[audio->rawdatareadoffset],
-                                                       len*2, volume);
+            SDL_MixAudioFormat(stream, (Uint8 *)&audio->spillover[audio->rawdatareadoffset],
+                                                       audio->format, len*2, volume);
             mixed += len*2;
             audio->rawdatareadoffset += len;
             goto finished_mixing;
         }
-        SDL_MixAudio(stream, (Uint8 *)&audio->spillover[audio->rawdatareadoffset],
-                                                       copylen*2, volume);
+        SDL_MixAudioFormat(stream, (Uint8 *)&audio->spillover[audio->rawdatareadoffset],
+                                                       audio->format, copylen*2, volume);
         mixed += copylen*2;
         len -= copylen;
         stream += copylen*2;
@@ -503,7 +503,7 @@ int Play_MPEGaudio(MPEGaudio *audio, Uint8 *stream, int len)
     audio->rawdatawriteoffset = 0;
     if ( audio->run(1) ) {
         assert(audio->rawdatawriteoffset > len);
-        SDL_MixAudio(stream, (Uint8 *) audio->spillover, len*2, volume);
+        SDL_MixAudioFormat(stream, (Uint8 *) audio->spillover, audio->format, len*2, volume);
         mixed += len*2;
         audio->rawdatareadoffset = len;
     } else {