I ran rhythmbox with valgrind (~30 minutes playing various file types, using the sound indicator and keyboard shortcuts to play/stop/switch between songs, with the shuffle mode)

==10276== LEAK SUMMARY:
==10276==    definitely lost: 5,021,263 bytes in 329 blocks
==10276==    indirectly lost: 8,623,848 bytes in 2,381 blocks
==10276==      possibly lost: 31,876,828 bytes in 16,677 blocks
==10276==    still reachable: 33,412,186 bytes in 278,143 blocks
==10276==         suppressed: 0 bytes in 0 blocks
==10276== Reachable blocks (those to which a pointer was found) are not shown.
==10276== To see them, rerun with: --leak-check=full --show-reachable=yes
==10276==
==10276== ERROR SUMMARY: 15930 errors from 8359 contexts (suppressed: 31 from 3)


2 biggest leaks:

==10276== 8,215,364 (840 direct, 8,214,524 indirect) bytes in 35 blocks are definitely lost in loss record 67,187 of 67,188
==10276==    at 0x4C29DB4: calloc (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==10276==    by 0x5BF6AE0: g_malloc0 (in /lib/x86_64-linux-gnu/libglib-2.0.so.0.3200.3)
==10276==    by 0x4E79BE0: load_external_art_cb (rb-shell.c:516)
==10276==    by 0xD841A13: ffi_call_unix64 (in /usr/lib/x86_64-linux-gnu/libffi.so.6.0.0)
==10276==    by 0xD841434: ffi_call (in /usr/lib/x86_64-linux-gnu/libffi.so.6.0.0)
==10276==    by 0x596A50A: g_cclosure_marshal_generic (in /usr/lib/x86_64-linux-gnu/libgobject-2.0.so.0.3200.3)
==10276==    by 0x5969C1A: g_closure_invoke (in /usr/lib/x86_64-linux-gnu/libgobject-2.0.so.0.3200.3)
==10276==    by 0x597AD70: ??? (in /usr/lib/x86_64-linux-gnu/libgobject-2.0.so.0.3200.3)
==10276==    by 0x5982D7D: g_signal_emit_valist (in /usr/lib/x86_64-linux-gnu/libgobject-2.0.so.0.3200.3)
==10276==    by 0x5983241: g_signal_emit (in /usr/lib/x86_64-linux-gnu/libgobject-2.0.so.0.3200.3)
==10276==    by 0x4EB5741: do_load_request (rb-ext-db.c:625)
==10276==    by 0x5475E7B: ??? (in /usr/lib/x86_64-linux-gnu/libgio-2.0.so.0.3200.3)
==10276==    by 0x546515D: ??? (in /usr/lib/x86_64-linux-gnu/libgio-2.0.so.0.3200.3)
==10276==    by 0x5C13247: ??? (in /lib/x86_64-linux-gnu/libglib-2.0.so.0.3200.3)
==10276==    by 0x5C129E4: ??? (in /lib/x86_64-linux-gnu/libglib-2.0.so.0.3200.3)
==10276==    by 0x5EA5E99: start_thread (pthread_create.c:308)
==10276==    by 0x61AECBC: clone (clone.S:112)
==10276==
==10276== 17,916,336 bytes in 15 blocks are possibly lost in loss record 67,188 of 67,188
==10276==    at 0x4C2B6CD: malloc (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==10276==    by 0x9BA8F64: gdk_pixbuf_new (in /usr/lib/x86_64-linux-gnu/libgdk_pixbuf-2.0.so.0.2600.1)
==10276==    by 0x3A5A9D25: ??? (in /usr/lib/x86_64-linux-gnu/gdk-pixbuf-2.0/2.10.0/loaders/libpixbufloader-jpeg.so)
==10276==    by 0x9BAED14: ??? (in /usr/lib/x86_64-linux-gnu/libgdk_pixbuf-2.0.so.0.2600.1)
==10276==    by 0x9BAFC2A: gdk_pixbuf_loader_write (in /usr/lib/x86_64-linux-gnu/libgdk_pixbuf-2.0.so.0.2600.1)
==10276==    by 0x4E79BA6: load_external_art_cb (rb-shell.c:500)
==10276==    by 0xD841A13: ffi_call_unix64 (in /usr/lib/x86_64-linux-gnu/libffi.so.6.0.0)
==10276==    by 0xD841434: ffi_call (in /usr/lib/x86_64-linux-gnu/libffi.so.6.0.0)
==10276==    by 0x596A50A: g_cclosure_marshal_generic (in /usr/lib/x86_64-linux-gnu/libgobject-2.0.so.0.3200.3)
==10276==    by 0x5969C1A: g_closure_invoke (in /usr/lib/x86_64-linux-gnu/libgobject-2.0.so.0.3200.3)
==10276==    by 0x597AD70: ??? (in /usr/lib/x86_64-linux-gnu/libgobject-2.0.so.0.3200.3)
==10276==    by 0x5982D7D: g_signal_emit_valist (in /usr/lib/x86_64-linux-gnu/libgobject-2.0.so.0.3200.3)
==10276==    by 0x5983241: g_signal_emit (in /usr/lib/x86_64-linux-gnu/libgobject-2.0.so.0.3200.3)
==10276==    by 0x4EB5741: do_load_request (rb-ext-db.c:625)
==10276==    by 0x5475E7B: ??? (in /usr/lib/x86_64-linux-gnu/libgio-2.0.so.0.3200.3)
==10276==    by 0x546515D: ??? (in /usr/lib/x86_64-linux-gnu/libgio-2.0.so.0.3200.3)
==10276==    by 0x5C13247: ??? (in /lib/x86_64-linux-gnu/libglib-2.0.so.0.3200.3)
==10276==    by 0x5C129E4: ??? (in /lib/x86_64-linux-gnu/libglib-2.0.so.0.3200.3)
==10276==    by 0x5EA5E99: start_thread (pthread_create.c:308)
==10276==    by 0x61AECBC: clone (clone.S:112)


I can't upload the whole valgrind log (23MB) currently because Launchpad timeout. I will retry later.