avformat/matroskaenc: Add option to shift data to write cues at front

This is similar to the faststart option of the mov muxer, yet
in contrast to it it works together with reserve_index_space
(the equivalent to reserved_moov_size): If the reserved space
does not suffice, the data is shifted; if not, the Cues are
written at the front without shifting the data.
Several tests that cover (not only) this have been added.

Implements #7017.

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

2 files changed, 32 insertions, 12 deletions

diff --git a/libavformat/matroskaenc.c b/libavformat/matroskaenc.c
index 152312102a..41b2df7dbf 100644
--- a/libavformat/matroskaenc.c
+++ b/libavformat/matroskaenc.c
@@ -161,6 +161,7 @@ typedef struct MatroskaMuxContext {
     int                 allow_raw_vfw;
     int                 flipped_raw_rgb;
     int                 default_mode;
+    int                 move_cues_to_front;
 
     uint32_t            segment_uid[4];
 } MatroskaMuxContext;
@@ -566,7 +567,8 @@ static int mkv_add_cuepoint(MatroskaMuxContext *mkv, int stream, int64_t ts,
 }
 
 static int mkv_assemble_cues(AVStream **streams, AVIOContext *dyn_cp,
-                             mkv_cues *cues, mkv_track *tracks, int num_tracks)
+                             const mkv_cues *cues, mkv_track *tracks, int num_tracks,
+                             uint64_t offset)
 {
     AVIOContext *cuepoint;
     int ret;
@@ -597,7 +599,7 @@ static int mkv_assemble_cues(AVStream **streams, AVIOContext *dyn_cp,
             tracks[idx].has_cue = 1;
             track_positions = start_ebml_master(cuepoint, MATROSKA_ID_CUETRACKPOSITION, MAX_CUETRACKPOS_SIZE);
             put_ebml_uint(cuepoint, MATROSKA_ID_CUETRACK           , tracks[idx].track_num);
-            put_ebml_uint(cuepoint, MATROSKA_ID_CUECLUSTERPOSITION , entry->cluster_pos);
+            put_ebml_uint(cuepoint, MATROSKA_ID_CUECLUSTERPOSITION , entry->cluster_pos + offset);
             put_ebml_uint(cuepoint, MATROSKA_ID_CUERELATIVEPOSITION, entry->relative_pos);
             if (entry->duration > 0)
                 put_ebml_uint(cuepoint, MATROSKA_ID_CUEDURATION    , entry->duration);
@@ -1984,12 +1986,14 @@ static int mkv_write_header(AVFormatContext *s)
         put_ebml_void(pb, s->metadata_header_padding);
     }
 
-    if (mkv->reserve_cues_space) {
+    if (mkv->reserve_cues_space || mkv->move_cues_to_front) {
         if (IS_SEEKABLE(pb, mkv)) {
             mkv->cues_pos = avio_tell(pb);
-            if (mkv->reserve_cues_space == 1)
-                mkv->reserve_cues_space++;
-            put_ebml_void(pb, mkv->reserve_cues_space);
+            if (mkv->reserve_cues_space >= 1) {
+                if (mkv->reserve_cues_space == 1)
+                    mkv->reserve_cues_space++;
+                put_ebml_void(pb, mkv->reserve_cues_space);
+            }
         } else
             mkv->reserve_cues_space = -1;
     }
@@ -2575,25 +2579,31 @@ static int mkv_write_trailer(AVFormatContext *s)
 
     if (mkv->cues.num_entries && mkv->reserve_cues_space >= 0) {
         AVIOContext *cues = NULL;
-        uint64_t size;
+        uint64_t size, offset = 0;
         int length_size = 0;
 
+redo_cues:
         ret = start_ebml_master_crc32(&cues, mkv);
         if (ret < 0)
             return ret;
 
         ret = mkv_assemble_cues(s->streams, cues, &mkv->cues,
-                                mkv->tracks, s->nb_streams);
+                                mkv->tracks, s->nb_streams, offset);
         if (ret < 0) {
             ffio_free_dyn_buf(&cues);
             return ret;
         }
 
-        if (mkv->reserve_cues_space) {
+        if (mkv->reserve_cues_space || mkv->move_cues_to_front) {
             size  = avio_tell(cues);
             length_size = ebml_length_size(size);
             size += 4 + length_size;
-            if (mkv->reserve_cues_space < size) {
+            if (offset + mkv->reserve_cues_space < size) {
+                if (mkv->move_cues_to_front) {
+                    offset = size - mkv->reserve_cues_space;
+                    ffio_reset_dyn_buf(cues);
+                    goto redo_cues;
+                }
                 av_log(s, AV_LOG_WARNING,
                        "Insufficient space reserved for Cues: "
                        "%d < %"PRIu64". No Cues will be output.\n",
@@ -2601,6 +2611,15 @@ static int mkv_write_trailer(AVFormatContext *s)
                 ret2 = AVERROR(EINVAL);
                 goto after_cues;
             } else {
+                if (offset) {
+                    ret = ff_format_shift_data(s, mkv->cues_pos + mkv->reserve_cues_space,
+                                               offset);
+                    if (ret < 0) {
+                        ffio_free_dyn_buf(&cues);
+                        return ret;
+                    }
+                    endpos += offset;
+                }
                 if ((ret64 = avio_seek(pb, mkv->cues_pos, SEEK_SET)) < 0) {
                     ffio_free_dyn_buf(&cues);
                     return ret64;
@@ -2623,7 +2642,7 @@ static int mkv_write_trailer(AVFormatContext *s)
         if (mkv->reserve_cues_space) {
             if (size < mkv->reserve_cues_space)
                 put_ebml_void(pb, mkv->reserve_cues_space - size);
-        } else
+        } else if (!mkv->move_cues_to_front)
             endpos = avio_tell(pb);
     }
 
@@ -2848,6 +2867,7 @@ 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 },
+    { "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 },
     { "dash", "Create a WebM file conforming to WebM DASH specification", OFFSET(is_dash), AV_OPT_TYPE_BOOL, { .i64 = 0 }, 0, 1, FLAGS },
diff --git a/libavformat/version.h b/libavformat/version.h
index 77f4b46712..bd014e907e 100644
--- a/libavformat/version.h
+++ b/libavformat/version.h
@@ -33,7 +33,7 @@
 // Also please add any ticket numbers that you believe might be affected here
 #define LIBAVFORMAT_VERSION_MAJOR  59
 #define LIBAVFORMAT_VERSION_MINOR  17
-#define LIBAVFORMAT_VERSION_MICRO 100
+#define LIBAVFORMAT_VERSION_MICRO 101
 
 #define LIBAVFORMAT_VERSION_INT AV_VERSION_INT(LIBAVFORMAT_VERSION_MAJOR, \
                                                LIBAVFORMAT_VERSION_MINOR, \