strmbase: COM cleanup for cleanup SourceSeeking.
diff --git a/dlls/quartz/avisplit.c b/dlls/quartz/avisplit.c
index 3a50de5..bcfdeb1 100644
--- a/dlls/quartz/avisplit.c
+++ b/dlls/quartz/avisplit.c
@@ -102,7 +102,7 @@
 
 static inline AVISplitterImpl *impl_from_IMediaSeeking( IMediaSeeking *iface )
 {
-    return (AVISplitterImpl *)((char*)iface - FIELD_OFFSET(AVISplitterImpl, Parser.sourceSeeking.lpVtbl));
+    return CONTAINING_RECORD(iface, AVISplitterImpl, Parser.sourceSeeking.IMediaSeeking_iface);
 }
 
 /* The threading stuff cries for an explanation
diff --git a/dlls/quartz/mpegsplit.c b/dlls/quartz/mpegsplit.c
index acb72ed..f2e1138 100644
--- a/dlls/quartz/mpegsplit.c
+++ b/dlls/quartz/mpegsplit.c
@@ -78,7 +78,7 @@
 
 static inline MPEGSplitterImpl *impl_from_IMediaSeeking( IMediaSeeking *iface )
 {
-    return (MPEGSplitterImpl *)((char*)iface - FIELD_OFFSET(MPEGSplitterImpl, Parser.sourceSeeking.lpVtbl));
+    return CONTAINING_RECORD(iface, MPEGSplitterImpl, Parser.sourceSeeking.IMediaSeeking_iface);
 }
 
 static int MPEGSplitter_head_check(const BYTE *header)
diff --git a/dlls/quartz/parser.c b/dlls/quartz/parser.c
index 784c528..c1d041a 100644
--- a/dlls/quartz/parser.c
+++ b/dlls/quartz/parser.c
@@ -50,7 +50,7 @@
 
 static inline ParserImpl *impl_from_IMediaSeeking( IMediaSeeking *iface )
 {
-    return (ParserImpl *)((char*)iface - FIELD_OFFSET(ParserImpl, sourceSeeking.lpVtbl));
+    return CONTAINING_RECORD(iface, ParserImpl, sourceSeeking.IMediaSeeking_iface);
 }
 
 /* FIXME: WRONG */
diff --git a/dlls/quartz/waveparser.c b/dlls/quartz/waveparser.c
index a1b58e5..bc0615e 100644
--- a/dlls/quartz/waveparser.c
+++ b/dlls/quartz/waveparser.c
@@ -50,7 +50,7 @@
 
 static inline WAVEParserImpl *impl_from_IMediaSeeking( IMediaSeeking *iface )
 {
-    return (WAVEParserImpl*)((char*)iface - FIELD_OFFSET(WAVEParserImpl, Parser.sourceSeeking.lpVtbl));
+    return CONTAINING_RECORD(iface, WAVEParserImpl, Parser.sourceSeeking.IMediaSeeking_iface);
 }
 
 static LONGLONG bytepos_to_duration(WAVEParserImpl *This, LONGLONG bytepos)