demux_mkv: passthrough BlockAdditions for libvpx alpha

Dumb but simple thing. Requires the FFmpeg libvpx decoder wrapper, as
its native decoder doesn't support alpha.

TOOLS/matroska.py

@@ -69,6 +69,12 @@ elements_matroska = (
                 'BlockDuration, 9b, uint',
                 'ReferenceBlock*, fb, sint',
                 'DiscardPadding,  75A2, sint',
+                'BlockAdditions, 75A1, sub', (
+                    'BlockMore*, A6, sub', (
+                        'BlockAddID, EE, uint',
+                        'BlockAdditional, A5, binary',
+                    ),
+                ),
             ),
             'SimpleBlock*, a3, binary',
         ),

demux/demux_mkv.c

@@ -162,6 +162,7 @@ struct block_info {
     bstr data;
     void *alloc;
     int64_t filepos;
+    struct ebml_block_additions *additions;
 };
 
 typedef struct mkv_demuxer {
@@ -2392,6 +2393,8 @@ static void free_block(struct block_info *block)
     free(block->alloc);
     block->alloc = NULL;
     block->data = (bstr){0};
+    talloc_free(block->additions);
+    block->additions = NULL;
 }
 
 static void index_block(demuxer_t *demuxer, struct block_info *block)
@@ -2552,6 +2555,15 @@ static int handle_block(demuxer_t *demuxer, struct block_info *block_info)
                     block_info->discardpadding / 1e9 * srate);
                 mkv_d->a_skip_preroll = 0;
             }
+            if (block_info->additions) {
+                for (int n = 0; n < block_info->additions->n_block_more; n++) {
+                    struct ebml_block_more *add =
+                        &block_info->additions->block_more[n];
+                    int64_t id = add->n_block_add_id ? add->block_add_id : 1;
+                    demux_packet_add_blockadditional(dp, id,
+                        add->block_additional.start, add->block_additional.len);
+                }
+            }
 
             mkv_parse_and_add_packet(demuxer, track, dp);
             talloc_free_children(track->parser_tmp);
@@ -2607,6 +2619,21 @@ static int read_block_group(demuxer_t *demuxer, int64_t end,
             block->keyframe = false;
             break;
 
+        case MATROSKA_ID_BLOCKADDITIONS:;
+            struct ebml_block_additions additions = {0};
+            struct ebml_parse_ctx parse_ctx = {demuxer->log};
+            if (ebml_read_element(s, &parse_ctx, &additions,
+                                  &ebml_block_additions_desc) < 0)
+                return -1;
+            if (additions.n_block_more > 0) {
+                block->additions =
+                    talloc_memdup(NULL, &additions, sizeof(additions));
+                talloc_steal(block->additions, parse_ctx.talloc_ctx);
+                parse_ctx.talloc_ctx = NULL;
+            }
+            talloc_free(parse_ctx.talloc_ctx);
+            break;
+
         case MATROSKA_ID_CLUSTER:
         case EBML_ID_INVALID:
             goto error;

demux/packet.c

@@ -133,7 +133,7 @@ struct demux_packet *demux_copy_packet(struct demux_packet *dp)
 int demux_packet_set_padding(struct demux_packet *dp, int start, int end)
 {
 #if LIBAVCODEC_VERSION_MICRO >= 100
-    if (!start  && !end)
+    if (!start && !end)
         return 0;
     if (!dp->avpacket)
         return -1;
@@ -146,3 +146,21 @@ int demux_packet_set_padding(struct demux_packet *dp, int start, int end)
 #endif
     return 0;
 }
+
+int demux_packet_add_blockadditional(struct demux_packet *dp, uint64_t id,
+                                     void *data, size_t size)
+{
+#if LIBAVCODEC_VERSION_MICRO >= 100
+    if (!dp->avpacket)
+        return -1;
+    uint8_t *sd =  av_packet_new_side_data(dp->avpacket,
+                                           AV_PKT_DATA_MATROSKA_BLOCKADDITIONAL,
+                                           8 + size);
+    if (!sd)
+        return -1;
+    AV_WB64(sd, id);
+    if (size > 0)
+        memcpy(sd + 8, data, size);
+#endif
+    return 0;
+}

demux/packet.h

@@ -55,5 +55,7 @@ struct demux_packet *demux_copy_packet(struct demux_packet *dp);
 void demux_packet_copy_attribs(struct demux_packet *dst, struct demux_packet *src);
 
 int demux_packet_set_padding(struct demux_packet *dp, int start, int end);
+int demux_packet_add_blockadditional(struct demux_packet *dp, uint64_t id,
+                                     void *data, size_t size);
 
 #endif /* MPLAYER_DEMUX_PACKET_H */