avformat/matroskaenc: Write level 1 elements in one go

Up until now, writing level 1 elements proceeded as follows: First, the
element id was written to the ordinary output AVIOContext and a dynamic
buffer was opened for the content of the level 1 element in
start_ebml_master_crc32(). Then this buffer was actually used and after it
was closed (in end_ebml_master_crc32()), the size field corresponding to
the buffer's size was written, after which the actual data was written.

This commit changes this: Nothing is written to the main AVIOContext any
more in start_ebml_master_crc32(). end_ebml_master_crc32() now writes
both the id, the length field as well as the data. This implies that
one can start a level 1 element in memory without outputting anything.
This is done to enable to test whether enough space has been reserved
for the Cues (if space has been reserved for them) before writing them.
A large duration between outputting the header and outputting the rest
could also break certain streaming usecases like the one from #8578
(which this commit fixes).
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@gmail.com>

libavformat/matroskaenc.c

@@ -325,26 +325,26 @@ static void end_ebml_master(AVIOContext *pb, ebml_master master)
     avio_seek(pb, pos, SEEK_SET);
 }
 
-static int start_ebml_master_crc32(AVIOContext *pb, AVIOContext **dyn_cp, MatroskaMuxContext *mkv,
-                                   uint32_t elementid)
+static int start_ebml_master_crc32(AVIOContext **dyn_cp, MatroskaMuxContext *mkv)
 {
     int ret;
 
     if ((ret = avio_open_dyn_buf(dyn_cp)) < 0)
         return ret;
 
-    put_ebml_id(pb, elementid);
     if (mkv->write_crc)
         put_ebml_void(*dyn_cp, 6); /* Reserve space for CRC32 so position/size calculations using avio_tell() take it into account */
 
     return 0;
 }
 
-static void end_ebml_master_crc32(AVIOContext *pb, AVIOContext **dyn_cp, MatroskaMuxContext *mkv)
+static void end_ebml_master_crc32(AVIOContext *pb, AVIOContext **dyn_cp,
+                                  MatroskaMuxContext *mkv, uint32_t id)
 {
     uint8_t *buf, crc[4];
     int size, skip = 0;
 
+    put_ebml_id(pb, id);
     size = avio_close_dyn_buf(*dyn_cp, &buf);
     put_ebml_num(pb, size, 0);
     if (mkv->write_crc) {
@@ -362,13 +362,14 @@ static void end_ebml_master_crc32(AVIOContext *pb, AVIOContext **dyn_cp, Matrosk
 * Complete ebml master without destroying the buffer, allowing for later updates
 */
 static void end_ebml_master_crc32_preliminary(AVIOContext *pb, AVIOContext **dyn_cp, MatroskaMuxContext *mkv,
-                                              int64_t *pos)
+                                              uint32_t id, int64_t *pos)
 {
     uint8_t *buf;
     int size = avio_get_dyn_buf(*dyn_cp, &buf);
 
     *pos = avio_tell(pb);
 
+    put_ebml_id(pb, id);
     put_ebml_num(pb, size, 0);
     avio_write(pb, buf, size);
 }
@@ -448,7 +449,7 @@ static int mkv_write_seekhead(AVIOContext *pb, MatroskaMuxContext *mkv,
     if ((ret64 = avio_seek(pb, seekhead->filepos, SEEK_SET)) < 0)
         return error_on_seek_failure ? ret64 : 0;
 
-    ret = start_ebml_master_crc32(pb, &dyn_cp, mkv, MATROSKA_ID_SEEKHEAD);
+    ret = start_ebml_master_crc32(&dyn_cp, mkv);
     if (ret < 0)
         return ret;
 
@@ -464,7 +465,7 @@ static int mkv_write_seekhead(AVIOContext *pb, MatroskaMuxContext *mkv,
         put_ebml_uint(dyn_cp, MATROSKA_ID_SEEKPOSITION, entry->segmentpos);
         end_ebml_master(dyn_cp, seekentry);
     }
-    end_ebml_master_crc32(pb, &dyn_cp, mkv);
+    end_ebml_master_crc32(pb, &dyn_cp, mkv, MATROSKA_ID_SEEKHEAD);
 
     remaining = seekhead->filepos + seekhead->reserved_size - avio_tell(pb);
     put_ebml_void(pb, remaining);
@@ -507,7 +508,7 @@ static int64_t mkv_write_cues(AVFormatContext *s, mkv_cues *cues, mkv_track *tra
     int ret;
 
     currentpos = avio_tell(pb);
-    ret = start_ebml_master_crc32(pb, &dyn_cp, mkv, MATROSKA_ID_CUES);
+    ret = start_ebml_master_crc32(&dyn_cp, mkv);
     if (ret < 0)
         return ret;
 
@@ -550,7 +551,7 @@ static int64_t mkv_write_cues(AVFormatContext *s, mkv_cues *cues, mkv_track *tra
         ffio_reset_dyn_buf(cuepoint);
     }
     ffio_free_dyn_buf(&cuepoint);
-    end_ebml_master_crc32(pb, &dyn_cp, mkv);
+    end_ebml_master_crc32(pb, &dyn_cp, mkv, MATROSKA_ID_CUES);
 
     return currentpos;
 }
@@ -1372,7 +1373,7 @@ static int mkv_write_tracks(AVFormatContext *s)
 
     mkv_add_seekhead_entry(mkv, MATROSKA_ID_TRACKS, avio_tell(pb));
 
-    ret = start_ebml_master_crc32(pb, &mkv->tracks_bc, mkv, MATROSKA_ID_TRACKS);
+    ret = start_ebml_master_crc32(&mkv->tracks_bc, mkv);
     if (ret < 0)
         return ret;
 
@@ -1387,9 +1388,10 @@ static int mkv_write_tracks(AVFormatContext *s)
     }
 
     if ((pb->seekable & AVIO_SEEKABLE_NORMAL) && !mkv->is_live)
-        end_ebml_master_crc32_preliminary(pb, &mkv->tracks_bc, mkv, &mkv->tracks_pos);
+        end_ebml_master_crc32_preliminary(pb, &mkv->tracks_bc, mkv,
+                                          MATROSKA_ID_TRACKS, &mkv->tracks_pos);
     else
-        end_ebml_master_crc32(pb, &mkv->tracks_bc, mkv);
+        end_ebml_master_crc32(pb, &mkv->tracks_bc, mkv, MATROSKA_ID_TRACKS);
 
     return 0;
 }
@@ -1407,7 +1409,7 @@ static int mkv_write_chapters(AVFormatContext *s)
 
     mkv_add_seekhead_entry(mkv, MATROSKA_ID_CHAPTERS, avio_tell(pb));
 
-    ret = start_ebml_master_crc32(pb, &dyn_cp, mkv, MATROSKA_ID_CHAPTERS);
+    ret = start_ebml_master_crc32(&dyn_cp, mkv);
     if (ret < 0) return ret;
 
     editionentry = start_ebml_master(dyn_cp, MATROSKA_ID_EDITIONENTRY, 0);
@@ -1445,7 +1447,7 @@ static int mkv_write_chapters(AVFormatContext *s)
         end_ebml_master(dyn_cp, chapteratom);
     }
     end_ebml_master(dyn_cp, editionentry);
-    end_ebml_master_crc32(pb, &dyn_cp, mkv);
+    end_ebml_master_crc32(pb, &dyn_cp, mkv, MATROSKA_ID_CHAPTERS);
 
     mkv->wrote_chapters = 1;
     return 0;
@@ -1496,7 +1498,7 @@ static int mkv_write_tag_targets(AVFormatContext *s, uint32_t elementid,
     if (!mkv->tags_bc) {
         mkv_add_seekhead_entry(mkv, MATROSKA_ID_TAGS, avio_tell(s->pb));
 
-        ret = start_ebml_master_crc32(s->pb, &mkv->tags_bc, mkv, MATROSKA_ID_TAGS);
+        ret = start_ebml_master_crc32(&mkv->tags_bc, mkv);
         if (ret < 0)
             return ret;
     }
@@ -1641,9 +1643,10 @@ static int mkv_write_tags(AVFormatContext *s)
 
     if (mkv->tags_bc) {
         if ((s->pb->seekable & AVIO_SEEKABLE_NORMAL) && !mkv->is_live)
-            end_ebml_master_crc32_preliminary(s->pb, &mkv->tags_bc, mkv, &mkv->tags_pos);
+            end_ebml_master_crc32_preliminary(s->pb, &mkv->tags_bc, mkv,
+                                              MATROSKA_ID_TAGS, &mkv->tags_pos);
         else
-            end_ebml_master_crc32(s->pb, &mkv->tags_bc, mkv);
+            end_ebml_master_crc32(s->pb, &mkv->tags_bc, mkv, MATROSKA_ID_TAGS);
     }
     return 0;
 }
@@ -1666,7 +1669,7 @@ static int mkv_write_attachments(AVFormatContext *s)
 
     mkv_add_seekhead_entry(mkv, MATROSKA_ID_ATTACHMENTS, avio_tell(pb));
 
-    ret = start_ebml_master_crc32(pb, &dyn_cp, mkv, MATROSKA_ID_ATTACHMENTS);
+    ret = start_ebml_master_crc32(&dyn_cp, mkv);
     if (ret < 0) return ret;
 
     for (i = 0; i < s->nb_streams; i++) {
@@ -1739,7 +1742,7 @@ static int mkv_write_attachments(AVFormatContext *s)
         mkv->attachments->entries[mkv->attachments->num_entries].stream_idx = i;
         mkv->attachments->entries[mkv->attachments->num_entries++].fileuid  = fileuid;
     }
-    end_ebml_master_crc32(pb, &dyn_cp, mkv);
+    end_ebml_master_crc32(pb, &dyn_cp, mkv, MATROSKA_ID_ATTACHMENTS);
 
     return 0;
 }
@@ -1818,7 +1821,7 @@ static int mkv_write_header(AVFormatContext *s)
 
     mkv_add_seekhead_entry(mkv, MATROSKA_ID_INFO, avio_tell(pb));
 
-    ret = start_ebml_master_crc32(pb, &mkv->info_bc, mkv, MATROSKA_ID_INFO);
+    ret = start_ebml_master_crc32(&mkv->info_bc, mkv);
     if (ret < 0)
         return ret;
     pb = mkv->info_bc;
@@ -1877,9 +1880,10 @@ static int mkv_write_header(AVFormatContext *s)
         }
     }
     if ((s->pb->seekable & AVIO_SEEKABLE_NORMAL) && !mkv->is_live)
-        end_ebml_master_crc32_preliminary(s->pb, &mkv->info_bc, mkv, &mkv->info_pos);
+        end_ebml_master_crc32_preliminary(s->pb, &mkv->info_bc, mkv,
+                                          MATROSKA_ID_INFO, &mkv->info_pos);
     else
-        end_ebml_master_crc32(s->pb, &mkv->info_bc, mkv);
+        end_ebml_master_crc32(s->pb, &mkv->info_bc, mkv, MATROSKA_ID_INFO);
     pb = s->pb;
 
     ret = mkv_write_tracks(s);
@@ -2167,7 +2171,7 @@ static void mkv_end_cluster(AVFormatContext *s)
 {
     MatroskaMuxContext *mkv = s->priv_data;
 
-    end_ebml_master_crc32(s->pb, &mkv->cluster_bc, mkv);
+    end_ebml_master_crc32(s->pb, &mkv->cluster_bc, mkv, MATROSKA_ID_CLUSTER);
     mkv->cluster_pos = -1;
     avio_write_marker(s->pb, AV_NOPTS_VALUE, AVIO_DATA_MARKER_FLUSH_POINT);
 }
@@ -2308,7 +2312,7 @@ static int mkv_write_packet_internal(AVFormatContext *s, AVPacket *pkt, int add_
 
     if (mkv->cluster_pos == -1) {
         mkv->cluster_pos = avio_tell(s->pb);
-        ret = start_ebml_master_crc32(s->pb, &mkv->cluster_bc, mkv, MATROSKA_ID_CLUSTER);
+        ret = start_ebml_master_crc32(&mkv->cluster_bc, mkv);
         if (ret < 0)
             return ret;
         put_ebml_uint(mkv->cluster_bc, MATROSKA_ID_CLUSTERTIMECODE, FFMAX(0, ts));
@@ -2474,7 +2478,7 @@ static int mkv_write_trailer(AVFormatContext *s)
     }
 
     if (mkv->cluster_bc) {
-        end_ebml_master_crc32(pb, &mkv->cluster_bc, mkv);
+        end_ebml_master_crc32(pb, &mkv->cluster_bc, mkv, MATROSKA_ID_CLUSTER);
     }
 
     ret = mkv_write_chapters(s);
@@ -2522,11 +2526,11 @@ static int mkv_write_trailer(AVFormatContext *s)
         av_log(s, AV_LOG_DEBUG, "end duration = %" PRIu64 "\n", mkv->duration);
         avio_seek(mkv->info_bc, mkv->duration_offset, SEEK_SET);
         put_ebml_float(mkv->info_bc, MATROSKA_ID_DURATION, mkv->duration);
-        end_ebml_master_crc32(pb, &mkv->info_bc, mkv);
+        end_ebml_master_crc32(pb, &mkv->info_bc, mkv, MATROSKA_ID_INFO);
 
         // write tracks master
         avio_seek(pb, mkv->tracks_pos, SEEK_SET);
-        end_ebml_master_crc32(pb, &mkv->tracks_bc, mkv);
+        end_ebml_master_crc32(pb, &mkv->tracks_bc, mkv, MATROSKA_ID_TRACKS);
 
         // update stream durations
         if (!mkv->is_live) {
@@ -2556,7 +2560,7 @@ static int mkv_write_trailer(AVFormatContext *s)
         }
         if (mkv->tags_bc && !mkv->is_live) {
             avio_seek(pb, mkv->tags_pos, SEEK_SET);
-            end_ebml_master_crc32(pb, &mkv->tags_bc, mkv);
+            end_ebml_master_crc32(pb, &mkv->tags_bc, mkv, MATROSKA_ID_TAGS);
         }
 
         avio_seek(pb, currentpos, SEEK_SET);