avformat/matroskaenc: Avoid allocations for SeekHead

Up until e7ddafd5, the Matroska muxer wrote two SeekHeads: One at the
beginning referencing the main level 1 elements (i.e. not the Clusters)
and one at the end, referencing the Clusters. This second SeekHead was
useless and has therefore been removed. Yet the SeekHead-related
functions and structures are still geared towards this usecase: They
are built around an allocated array of variable size that gets
reallocated every time an element is added to it although the maximum
number of Seek entries is a small compile-time constant, so that one should
rather include the array in the SeekHead structure itself; and said
structure should be contained in the MatroskaMuxContext instead of being
allocated separately.

The earlier code reserved space for a SeekHead with 10 entries, although
we currently write at most 6. Reducing said number implied that every
Matroska/Webm file will be 84 bytes smaller and required to adapt
several FATE tests; furthermore, the reserved amount overestimated the
amount needed for for the SeekHead's length field and how many bytes
need to be reserved to write a EBML Void element, bringing the total
reduction to 89 bytes.

This also fixes a potential segfault: If !mkv->is_live and if the
AVIOContext is initially unseekable when writing the header, the
SeekHead is already written when writing the header and this used to
free the SeekHead-related structures that have been allocated. But if
the AVIOContext happens to be seekable when writing the trailer, it will
be attempted to write the SeekHead again which will lead to segfaults
because the corresponding structures have already been freed.

Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@gmail.com>

2 files changed, 3 insertions, 3 deletions

diff --git a/tests/fate/matroska.mak b/tests/fate/matroska.mak
index 4aca4dc8eb..b9ed7322fd 100644
--- a/tests/fate/matroska.mak
+++ b/tests/fate/matroska.mak
@@ -12,7 +12,7 @@ fate-matroska-prores-header-insertion-bz2: CMD = framecrc -i $(TARGET_SAMPLES)/m
 FATE_MATROSKA-$(call DEMMUX, MATROSKA, MATROSKA) += fate-matroska-remux
 fate-matroska-remux: CMD = md5pipe -i $(TARGET_SAMPLES)/vp9-test-vectors/vp90-2-2pass-akiyo.webm -color_trc 4 -c:v copy -fflags +bitexact -strict -2 -f matroska
 fate-matroska-remux: CMP = oneline
-fate-matroska-remux: REF = e5457e5fa606d564a54914bd12f426c8
+fate-matroska-remux: REF = 49a60ef91cf7302ab7276f9373f8a429
 
 FATE_MATROSKA-$(call ALLYES, MATROSKA_DEMUXER VORBIS_PARSER) += fate-matroska-xiph-lacing
 fate-matroska-xiph-lacing: CMD = framecrc -i $(TARGET_SAMPLES)/mkv/xiph_lacing.mka -c:a copy
diff --git a/tests/fate/wavpack.mak b/tests/fate/wavpack.mak
index 286e17f2ae..a89cc1293d 100644
--- a/tests/fate/wavpack.mak
+++ b/tests/fate/wavpack.mak
@@ -91,12 +91,12 @@ fate-wavpack-matroskamode: CMD = md5 -i $(TARGET_SAMPLES)/wavpack/special/matros
 FATE_WAVPACK-$(call DEMMUX, WV, MATROSKA) += fate-wavpack-matroska_mux-mono
 fate-wavpack-matroska_mux-mono: CMD = md5pipe -i $(TARGET_SAMPLES)/wavpack/num_channels/mono_16bit_int.wv -c copy -fflags +bitexact -f matroska
 fate-wavpack-matroska_mux-mono: CMP = oneline
-fate-wavpack-matroska_mux-mono: REF = c5a2b46d8b31c9c2e7bfb436f9d56f02
+fate-wavpack-matroska_mux-mono: REF = 0a1a7c6d3b413925f8261c92d1d53363
 
 FATE_WAVPACK-$(call DEMMUX, WV, MATROSKA) += fate-wavpack-matroska_mux-61
 fate-wavpack-matroska_mux-61: CMD = md5pipe -i $(TARGET_SAMPLES)/wavpack/num_channels/eva_2.22_6.1_16bit-partial.wv -c copy -fflags +bitexact -f matroska
 fate-wavpack-matroska_mux-61: CMP = oneline
-fate-wavpack-matroska_mux-61: REF = 22fc2a591be22657d19cab89ad6eef55
+fate-wavpack-matroska_mux-61: REF = 1f012f7c237f46f2f63089ba84c589c5
 
 FATE_SAMPLES_AVCONV += $(FATE_WAVPACK-yes)
 fate-wavpack: $(FATE_WAVPACK-yes)