From a99b4abae8a6bbefbb3628cc59f8cc35854a005c Mon Sep 17 00:00:00 2001
From: Max Kellermann <max@musicpd.org>
Date: Wed, 1 Jul 2020 17:48:44 +0200
Subject: [PATCH] decoder/OpusHead: return pre-skip

---
 src/decoder/plugins/OpusDecoderPlugin.cxx | 8 +++++---
 src/decoder/plugins/OpusHead.cxx          | 5 ++++-
 src/decoder/plugins/OpusHead.hxx          | 3 ++-
 3 files changed, 11 insertions(+), 5 deletions(-)

diff --git a/src/decoder/plugins/OpusDecoderPlugin.cxx b/src/decoder/plugins/OpusDecoderPlugin.cxx
index 3b3c312af..8a262b901 100644
--- a/src/decoder/plugins/OpusDecoderPlugin.cxx
+++ b/src/decoder/plugins/OpusDecoderPlugin.cxx
@@ -136,8 +136,8 @@ MPDOpusDecoder::OnOggBeginning(const ogg_packet &packet)
 	if (opus_decoder != nullptr || !IsOpusHead(packet))
 		throw std::runtime_error("BOS packet must be OpusHead");
 
-	unsigned channels;
-	if (!ScanOpusHeader(packet.packet, packet.bytes, channels) ||
+	unsigned channels, pre_skip;
+	if (!ScanOpusHeader(packet.packet, packet.bytes, channels, pre_skip) ||
 	    !audio_valid_channel_count(channels))
 		throw std::runtime_error("Malformed BOS packet");
 
@@ -305,10 +305,12 @@ ReadAndParseOpusHead(OggSyncState &sync, OggStreamState &stream,
 		     unsigned &channels)
 {
 	ogg_packet packet;
+	unsigned pre_skip;
 
 	return OggReadPacket(sync, stream, packet) && packet.b_o_s &&
 		IsOpusHead(packet) &&
-		ScanOpusHeader(packet.packet, packet.bytes, channels) &&
+		ScanOpusHeader(packet.packet, packet.bytes, channels,
+			       pre_skip) &&
 		audio_valid_channel_count(channels);
 }
 
diff --git a/src/decoder/plugins/OpusHead.cxx b/src/decoder/plugins/OpusHead.cxx
index 2c7555c79..30d959f04 100644
--- a/src/decoder/plugins/OpusHead.cxx
+++ b/src/decoder/plugins/OpusHead.cxx
@@ -18,6 +18,7 @@
  */
 
 #include "OpusHead.hxx"
+#include "util/ByteOrder.hxx"
 
 #include <stdint.h>
 
@@ -31,12 +32,14 @@ struct OpusHead {
 };
 
 bool
-ScanOpusHeader(const void *data, size_t size, unsigned &channels_r)
+ScanOpusHeader(const void *data, size_t size, unsigned &channels_r,
+	       unsigned &pre_skip_r)
 {
 	const OpusHead *h = (const OpusHead *)data;
 	if (size < 19 || (h->version & 0xf0) != 0)
 		return false;
 
 	channels_r = h->channels;
+	pre_skip_r = FromLE16(h->pre_skip);
 	return true;
 }
diff --git a/src/decoder/plugins/OpusHead.hxx b/src/decoder/plugins/OpusHead.hxx
index 5bec73208..39b5f832a 100644
--- a/src/decoder/plugins/OpusHead.hxx
+++ b/src/decoder/plugins/OpusHead.hxx
@@ -23,6 +23,7 @@
 #include <stddef.h>
 
 bool
-ScanOpusHeader(const void *data, size_t size, unsigned &channels_r);
+ScanOpusHeader(const void *data, size_t size, unsigned &channels_r,
+	       unsigned &pre_skip_r);
 
 #endif