From c7aaabf573e1b042165f27f5f55ecd10bf18be2c Mon Sep 17 00:00:00 2001
From: bnnm <bananaman255@gmail.com>
Date: Sat, 29 Jun 2019 13:24:53 +0200
Subject: [PATCH] Fix XVAG MPEG encoder delay/gapless looping

---
 src/coding/mpeg_custom_utils.c | 17 +++++++++++------
 src/meta/xvag.c                | 21 +++++++++++++++++++--
 src/vgmstream.h                |  1 +
 3 files changed, 31 insertions(+), 8 deletions(-)

diff --git a/src/coding/mpeg_custom_utils.c b/src/coding/mpeg_custom_utils.c
index f0d62fa3..f0c3a913 100644
--- a/src/coding/mpeg_custom_utils.c
+++ b/src/coding/mpeg_custom_utils.c
@@ -78,18 +78,23 @@ int mpeg_custom_setup_init_default(STREAMFILE *streamFile, off_t start_offset, m
 
     //todo: test more: this improves the output, but seems formats aren't usually prepared
     // (and/or the num_samples includes all possible samples in file, so by discarding some it'll reach EOF)
-#if 0
+
     /* set encoder delay (samples to skip at the beginning of a stream) if needed, which varies with encoder used */
     switch(data->type) {
-        case MPEG_AHX: data->skip_samples = 480; break; /* observed default */
-        case MPEG_P3D: data->skip_samples = info.frame_samples; break; /* matches Radical ADPCM (PC) output */
+        //case MPEG_AHX: data->skip_samples = 480; break; /* observed default */
+        //case MPEG_P3D: data->skip_samples = info.frame_samples; break; /* matches Radical ADPCM (PC) output */
+
         /* FSBs (with FMOD DLLs) don't seem to need it. Particularly a few games (all from Wayforward?)
          * contain audible garbage at the beginning, but it's actually there in-game too */
-        case MPEG_FSB: data->skip_samples = 0;
-        default: break;
+        //case MPEG_FSB: data->skip_samples = 0; break;
+
+        case MPEG_XVAG: /* set in header and needed for gapless looping */
+            data->skip_samples = data->config.skip_samples; break;
+        default:
+            break;
     }
     data->samples_to_discard = data->skip_samples;
-#endif
+
 
     return 1;
 fail:
diff --git a/src/meta/xvag.c b/src/meta/xvag.c
index 1992619e..1fd65850 100644
--- a/src/meta/xvag.c
+++ b/src/meta/xvag.c
@@ -160,11 +160,28 @@ VGMSTREAM * init_vgmstream_xvag(STREAMFILE *streamFile) {
             if (xvag.layers > 1 && !(xvag.layers*1 == vgmstream->channels || xvag.layers*2 == vgmstream->channels)) goto fail;
 
             /* "mpin": mpeg info */
-            /*  0x00/04: mpeg version/layer?  other: unknown or repeats of "fmat" */
             if (!find_chunk(streamFile, 0x6D70696E,first_offset,0, &chunk_offset,NULL, xvag.big_endian, 1)) /*"mpin"*/
                 goto fail;
 
-            cfg.chunk_size = read_32bit(chunk_offset+0x1c,streamFile); /* fixed frame size */
+            /* all layers/subsongs share the same config; not very useful but for posterity:
+             * - 0x00: mpeg version
+             * - 0x04: mpeg layer
+             * - 0x08: bit rate
+             * - 0x0c: sample rate
+             * - 0x10: some version? (0x01-0x03)?
+             * - 0x14: channels per stream?
+             * - 0x18: channels per stream or total channels?
+             * - 0x1c: fixed frame size (always CBR)
+             * - 0x20: encoder delay (usually but not always 1201)
+             * - 0x24: number of samples
+             * - 0x28: some size?
+             * - 0x2c: ? (0x02)
+             * - 0x30: ? (0x00, 0x80)
+             * - 0x34: data size
+             * (rest is padding)
+             * */
+            cfg.chunk_size = read_32bit(chunk_offset+0x1c,streamFile);
+            cfg.skip_samples = read_32bit(chunk_offset+0x20,streamFile);
             cfg.interleave = cfg.chunk_size * xvag.factor;
 
             vgmstream->codec_data = init_mpeg_custom(streamFile, start_offset, &vgmstream->coding_type, vgmstream->channels, MPEG_XVAG, &cfg);
diff --git a/src/vgmstream.h b/src/vgmstream.h
index 3ee515ad..56c3ab08 100644
--- a/src/vgmstream.h
+++ b/src/vgmstream.h
@@ -1030,6 +1030,7 @@ typedef struct {
     int interleave; /* size of stream interleave */
     int encryption; /* encryption mode */
     int big_endian;
+    int skip_samples;
     /* for AHX */
     int cri_type;
     uint16_t cri_key1;