>From b8a59df6a484beb391898de9b8c38f7387ad7ee5 Mon Sep 17 00:00:00 2001
From: Jerome Martinez <[email protected]>
Date: Wed, 3 Sep 2025 21:33:50 +0200
Subject: [PATCH 2/7] matroskaenc: reserve_video_track_space option
The number of block additions is not known in advance, so we need to be able to
set more reserved space for when we add a lot more block additions.
It is also possible to reduce the reserved space (or even eliminate it) for
those who want to keep the smallest header possible.
---
libavformat/matroskaenc.c | 82 ++++++++++++++++++++++++++++-----------
1 file changed, 59 insertions(+), 23 deletions(-)
diff --git a/libavformat/matroskaenc.c b/libavformat/matroskaenc.c
index 5339b6fd33..c7b804a3e5 100644
--- a/libavformat/matroskaenc.c
+++ b/libavformat/matroskaenc.c
@@ -80,6 +80,8 @@
* and so has avio_write(). */
#define MAX_SUPPORTED_EBML_LENGTH FFMIN(MAX_EBML_LENGTH, INT_MAX)
+#define MAX_MATROSKA_BLOCK_ADD_ITU_T_T35 1 /* currently only 1 such element is
supported */
+
#define MODE_MATROSKAv2 0x01
#define MODE_WEBM 0x02
@@ -196,6 +198,7 @@ typedef struct mkv_track {
int64_t duration;
int64_t duration_offset;
uint64_t max_blockaddid;
+ int itu_t_t35_count;
int64_t blockadditionmapping_offset;
int codecpriv_offset;
unsigned codecpriv_size; ///< size reserved for CodecPrivate
excluding header+length field
@@ -249,6 +252,7 @@ typedef struct MatroskaMuxContext {
int wrote_tags;
int reserve_cues_space;
+ int reserve_video_track_space;
int cluster_size_limit;
int64_t cluster_time_limit;
int write_crc;
@@ -1706,19 +1710,12 @@ static void
mkv_write_blockadditionmapping(AVFormatContext *s, const MatroskaMux
const AVDOVIDecoderConfigurationRecord *dovi;
const AVPacketSideData *sd;
- if (IS_SEEKABLE(s->pb, mkv) && par->codec_type == AVMEDIA_TYPE_VIDEO) {
+ if (IS_SEEKABLE(s->pb, mkv) && par->codec_type == AVMEDIA_TYPE_VIDEO &&
mkv->reserve_video_track_space > 1) {
track->blockadditionmapping_offset = avio_tell(pb);
// We can't know at this point if there will be a block with
BlockAdditions, so
// we either write the default value here, or a void element. Either
of them will
// be overwritten when finishing the track.
- if (par->codec_type == AVMEDIA_TYPE_VIDEO) {
- // Similarly, reserve space for an eventual
- // HDR10+ ITU T.35 metadata BlockAdditionMapping.
- put_ebml_void(pb, 4 /* MaxBlockAdditionID */
- + 3 /* BlockAdditionMapping */
- + 4 /* BlockAddIDValue */
- + 4 /* BlockAddIDType */);
- }
+ put_ebml_void(pb, mkv->reserve_video_track_space);
}
sd = av_packet_side_data_get(par->coded_side_data, par->nb_coded_side_data,
@@ -2796,6 +2793,31 @@ static void mkv_write_blockadditional(EbmlWriter
*writer, const uint8_t *buf,
ebml_writer_close_master(writer);
}
+static int mkv_simulate_blockadditional_header(AVFormatContext *s, int*
remaining_video_track_space, uint64_t additional_type, uint64_t additional_id)
+{
+ int size = 0;
+ size += uint_size(MATROSKA_ID_BLKADDIDTYPE) + 1 +
uint_size(additional_type);
+ size += uint_size(MATROSKA_ID_BLKADDIDVALUE) + 1 +
uint_size(additional_id);
+ size += uint_size(MATROSKA_ID_TRACKBLKADDMAPPING) + uint_size(size);
+ if (size > *remaining_video_track_space || *remaining_video_track_space -
size == 1) { /* min element full size is 2 so 1 byte is not something which can
be let alone */
+ av_log(s, AV_LOG_WARNING, "Block addition mapping in track header is
not written for type %"PRIu64" id %"PRIu64" due to lack of reserved bytes.\n",
additional_type, additional_id);
+ return 0;
+ }
+ *remaining_video_track_space -= size;
+ return 1;
+}
+
+static void mkv_write_blockadditional_header(AVFormatContext *s, uint64_t
additional_type, uint64_t additional_id)
+{
+ /* when you modify this function, adapt
mkv_simulate_blockadditional_header accordingly */
+ MatroskaMuxContext *mkv = s->priv_data;
+ AVIOContext *writer = mkv->track.bc;
+ ebml_master mapping_master = start_ebml_master(writer,
MATROSKA_ID_TRACKBLKADDMAPPING, 8);
+ put_ebml_uint(writer, MATROSKA_ID_BLKADDIDTYPE, additional_type);
+ put_ebml_uint(writer, MATROSKA_ID_BLKADDIDVALUE, additional_id);
+ end_ebml_master(writer, mapping_master);
+}
+
static int mkv_write_block(void *logctx, MatroskaMuxContext *mkv,
AVIOContext *pb, const AVCodecParameters *par,
mkv_track *track, const AVPacket *pkt,
@@ -2807,7 +2829,7 @@ static int mkv_write_block(void *logctx,
MatroskaMuxContext *mkv,
size_t side_data_size;
uint64_t additional_id;
unsigned track_number = track->track_num;
- EBML_WRITER(12);
+ EBML_WRITER(11 + MAX_MATROSKA_BLOCK_ADD_ITU_T_T35);
int ret;
mkv->cur_block.track = track;
@@ -2882,6 +2904,7 @@ static int mkv_write_block(void *logctx,
MatroskaMuxContext *mkv,
MATROSKA_BLOCK_ADD_ID_ITU_T_T35);
track->max_blockaddid = FFMAX(track->max_blockaddid,
MATROSKA_BLOCK_ADD_ID_ITU_T_T35);
+ track->itu_t_t35_count = 1;
}
}
@@ -3293,24 +3316,36 @@ after_cues:
for (unsigned i = 0; i < s->nb_streams; i++) {
const mkv_track *track = &mkv->tracks[i];
+ int remaining_video_track_space =
mkv->reserve_video_track_space;
+ int max_block_add_id_count = 0;
+ int max_block_add_id_size = 3 +
uint_size(track->max_blockaddid);
+ int block_type_t35_count = 0;
- if (!track->max_blockaddid ||
!track->blockadditionmapping_offset)
+ if (!track->max_blockaddid)
continue;
- // We reserved a single byte to write this value.
- av_assert0(track->max_blockaddid <= 0xFF);
+ /* check what is possible to write in the reserved space, in
priority order */
+ for (int i = 0; i < track->itu_t_t35_count; i++) {
+ block_type_t35_count +=
mkv_simulate_blockadditional_header(s, &remaining_video_track_space,
MATROSKA_BLOCK_ADD_ID_TYPE_ITU_T_T35, MATROSKA_BLOCK_ADD_ID_TYPE_ITU_T_T35);
+ }
+ if (remaining_video_track_space >= max_block_add_id_size &&
remaining_video_track_space != max_block_add_id_size + 1) { /* min element full
size is 2 so 1 byte is not something which can be let alone */
+ max_block_add_id_count++;
+ remaining_video_track_space -= max_block_add_id_size;
+ }
+ /* write what is possible to write in the reserved space */
+ /* when you modify this part, adapt the check part above
accordingly */
+ if (!track->blockadditionmapping_offset)
+ continue;
avio_seek(track_bc, track->blockadditionmapping_offset,
SEEK_SET);
-
- put_ebml_uint(track_bc, MATROSKA_ID_TRACKMAXBLKADDID,
- track->max_blockaddid);
- if (track->max_blockaddid == MATROSKA_BLOCK_ADD_ID_ITU_T_T35) {
- ebml_master mapping_master = start_ebml_master(track_bc,
MATROSKA_ID_TRACKBLKADDMAPPING, 8);
- put_ebml_uint(track_bc, MATROSKA_ID_BLKADDIDTYPE,
- MATROSKA_BLOCK_ADD_ID_TYPE_ITU_T_T35);
- put_ebml_uint(track_bc, MATROSKA_ID_BLKADDIDVALUE,
- MATROSKA_BLOCK_ADD_ID_ITU_T_T35);
- end_ebml_master(track_bc, mapping_master);
+ if (max_block_add_id_count) {
+ put_ebml_uint(track_bc, MATROSKA_ID_TRACKMAXBLKADDID,
track->max_blockaddid);
+ }
+ for (int i = 0; i < block_type_t35_count; i++) {
+ mkv_write_blockadditional_header(s,
MATROSKA_BLOCK_ADD_ID_TYPE_ITU_T_T35, MATROSKA_BLOCK_ADD_ID_ITU_T_T35);
+ }
+ if (remaining_video_track_space > 1) {
+ put_ebml_void(track_bc, remaining_video_track_space);
}
}
}
@@ -3545,6 +3580,7 @@ static const AVCodecTag additional_subtitle_tags[] = {
#define FLAGS AV_OPT_FLAG_ENCODING_PARAM
static const AVOption options[] = {
{ "reserve_index_space", "reserve a given amount of space (in bytes) at
the beginning of the file for the index (cues)", OFFSET(reserve_cues_space),
AV_OPT_TYPE_INT, { .i64 = 0 }, 0, INT_MAX, FLAGS },
+ { "reserve_video_track_space", "reserve a given amount of space (in bytes)
at the beginning of the file for the block additions (HDR, timecodes...)",
OFFSET(reserve_video_track_space), AV_OPT_TYPE_INT, { .i64 = 15 }, 0, INT_MAX,
FLAGS }, /* the number of block additions is not known in advance, so the
default value strikes a balance between the size of the reserved header size
and the maximum number of block additions that can be registered at the end of
writing */
{ "cues_to_front", "move Cues (the index) to the front by shifting data if
necessary", OFFSET(move_cues_to_front), AV_OPT_TYPE_BOOL, { .i64 = 0}, 0, 1,
FLAGS },
{ "cluster_size_limit", "store at most the provided amount of bytes in a
cluster", OFFSET(cluster_size_limit),
AV_OPT_TYPE_INT , { .i64 = -1 }, -1, INT_MAX, FLAGS },
{ "cluster_time_limit", "store at most the provided number of
milliseconds in a cluster",
OFFSET(cluster_time_limit), AV_OPT_TYPE_INT64, { .i64 = -1 }, -1, INT64_MAX,
FLAGS },
--
2.46.0.windows.1
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