From c5b514b57764d685a0657e9c74d53b6babb05cf7 Mon Sep 17 00:00:00 2001
From: bnnm <bananaman255@gmail.com>
Date: Sun, 23 Sep 2018 12:17:23 +0200
Subject: [PATCH] Improve UE4OPUS encoder delay and fix
 get_opus_samples_per_frame

---
 src/coding/ffmpeg_decoder_custom_opus.c | 32 ++++++++++++++++++++-----
 src/meta/ue4opus.c                      | 10 +++++---
 2 files changed, 33 insertions(+), 9 deletions(-)

diff --git a/src/coding/ffmpeg_decoder_custom_opus.c b/src/coding/ffmpeg_decoder_custom_opus.c
index b6f7cedb..0815ecfa 100644
--- a/src/coding/ffmpeg_decoder_custom_opus.c
+++ b/src/coding/ffmpeg_decoder_custom_opus.c
@@ -15,7 +15,7 @@
 
 static size_t make_oggs_first(uint8_t * buf, int buf_size, int channels, int skip, int sample_rate);
 static size_t make_oggs_page(uint8_t * buf, int buf_size, size_t data_size, int page_sequence, int granule);
-static uint32_t get_opus_samples_per_frame(const uint8_t * data, int Fs);
+static size_t opus_get_packet_samples(const uint8_t * buf, int len);
 
 typedef enum { OPUS_SWITCH, OPUS_UE4 } opus_type_t;
 typedef struct {
@@ -117,7 +117,7 @@ static size_t opus_io_read(STREAMFILE *streamfile, uint8_t *dest, off_t offset,
 
             /* create fake OggS page (full page for checksums) */
             read_streamfile(data->page_buffer+oggs_size, data->physical_offset + skip_size, data_size, streamfile); /* store page data */
-            data->samples_done += get_opus_samples_per_frame(data->page_buffer+oggs_size, 48000);
+            data->samples_done += opus_get_packet_samples(data->page_buffer+oggs_size, data_size);
             make_oggs_page(data->page_buffer,sizeof(data->page_buffer), data_size, data->sequence, data->samples_done);
             data->sequence++;
         }
@@ -288,8 +288,8 @@ static uint32_t get_oggs_checksum(uint8_t * data, int bytes) {
   return crc_reg;
 }
 
-/* from opus_decoder.c */
-static uint32_t get_opus_samples_per_frame(const uint8_t * data, int Fs) {
+/* from opus_decoder.c's opus_packet_get_samples_per_frame */
+static uint32_t opus_packet_get_samples_per_frame(const uint8_t * data, int Fs) {
     int audiosize;
     if (data[0]&0x80)
     {
@@ -308,6 +308,22 @@ static uint32_t get_opus_samples_per_frame(const uint8_t * data, int Fs) {
     return audiosize;
 }
 
+/* from opus_decoder.c's opus_packet_get_nb_frames */
+static int opus_packet_get_nb_frames(const uint8_t * packet, int len) {
+   int count;
+   if (len<1)
+      return 0;
+   count = packet[0]&0x3;
+   if (count==0)
+      return 1;
+   else if (count!=3)
+      return 2;
+   else if (len<2)
+      return 0;
+   else
+      return packet[1]&0x3F;
+}
+
 /* ******************************** */
 
 static size_t make_oggs_page(uint8_t * buf, int buf_size, size_t data_size, int page_sequence, int granule) {
@@ -440,6 +456,10 @@ fail:
 
 #ifdef VGM_USE_FFMPEG
 
+static size_t opus_get_packet_samples(const uint8_t * buf, int len) {
+    return opus_packet_get_nb_frames(buf, len) * opus_packet_get_samples_per_frame(buf, 48000);
+}
+
 static size_t custom_opus_get_samples(off_t offset, size_t data_size, int sample_rate, STREAMFILE *streamFile, opus_type_t type) {
     size_t num_samples = 0;
     off_t end_offset = offset + data_size;
@@ -467,8 +487,8 @@ static size_t custom_opus_get_samples(off_t offset, size_t data_size, int sample
                 return 0;
         }
 
-        read_streamfile(buf, offset+skip_size, 0x04, streamFile);
-        num_samples += get_opus_samples_per_frame(buf, sample_rate);
+        read_streamfile(buf, offset+skip_size, 0x04, streamFile); /* at least 0x02 */
+        num_samples += opus_get_packet_samples(buf, 0x04);
 
         offset += skip_size + data_size;
     }
diff --git a/src/meta/ue4opus.c b/src/meta/ue4opus.c
index aba2b15e..6e13f5a7 100644
--- a/src/meta/ue4opus.c
+++ b/src/meta/ue4opus.c
@@ -21,12 +21,16 @@ VGMSTREAM * init_vgmstream_ue4opus(STREAMFILE *streamFile) {
 
 
     sample_rate = (uint16_t)read_16bitLE(0x08, streamFile);
-    num_samples = read_32bitLE(0x0a, streamFile);
+    num_samples = read_32bitLE(0x0a, streamFile); /* may be less or equal to file num_samples */
     channel_count = read_8bit(0x0e, streamFile);
     /* 0x0f(2): frame count */
-    skip = 0; //todo test
     loop_flag = 0;
 
+    /* UE4Opus encodes 60ms (music) or 120ms (voice) frames, and encoder delay seems 1/8
+     * of samples per frame (may be more complex but wave looks ok-ish) */
+    //todo does UE4 actually care about encoder delay?
+    skip = (60 * 48000 / 1000) / 8; /* 48000 is the internal/resampled rate */
+
     start_offset = 0x11;
     data_size = get_streamfile_size(streamFile) - start_offset;
 
@@ -37,7 +41,7 @@ VGMSTREAM * init_vgmstream_ue4opus(STREAMFILE *streamFile) {
 
     vgmstream->meta_type = meta_UE4OPUS;
     vgmstream->sample_rate = sample_rate;
-    vgmstream->num_samples = num_samples;
+    vgmstream->num_samples = num_samples - skip;
 
 #ifdef VGM_USE_FFMPEG
     {