Adding support for muxing VP8 Alpha files

This patch adds support for muxing VP8 Alpha Files. The Alpha channel data is
placed in BlockAdditional element of the matroska container. More information
& exact spec on how this is implemented can be found here: http://goo.gl/wCP1y

Signed-off-by: Vignesh Venkatasubramanian <vigneshv@google.com>
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

diff --git a/libavformat/matroskaenc.c b/libavformat/matroskaenc.c
index 371b9d0bf2bb56035622fb89fc905b79aaf2808d..6e5daf4e4af53668f9e7989cdd25e744fd882ede 100644 (file)
--- a/libavformat/matroskaenc.c
+++ b/libavformat/matroskaenc.c
@@ -662,6 +662,12 @@ static int mkv_write_tracks(AVFormatContext *s)
                         put_ebml_uint(pb, MATROSKA_ID_VIDEOSTEREOMODE, st_mode);
                 }
 
+                if ((tag = av_dict_get(st->metadata, "alpha_mode", NULL, 0)) ||
+                    (tag = av_dict_get( s->metadata, "alpha_mode", NULL, 0)) ||
+                    (codec->pix_fmt == AV_PIX_FMT_YUVA420P)) {
+                    put_ebml_uint(pb, MATROSKA_ID_VIDEOALPHAMODE, 1);
+                }
+
                 if (st->sample_aspect_ratio.num) {
                     int64_t d_width = av_rescale(codec->width, st->sample_aspect_ratio.num, st->sample_aspect_ratio.den);
                     if (d_width > INT_MAX) {
@@ -1136,9 +1142,10 @@ static void mkv_write_block(AVFormatContext *s, AVIOContext *pb,
 {
     MatroskaMuxContext *mkv = s->priv_data;
     AVCodecContext *codec = s->streams[pkt->stream_index]->codec;
-    uint8_t *data = NULL;
-    int offset = 0, size = pkt->size;
+    uint8_t *data = NULL, *side_data = NULL;
+    int offset = 0, size = pkt->size, side_data_size = 0;
     int64_t ts = mkv->tracks[pkt->stream_index].write_dts ? pkt->dts : pkt->pts;
+    uint64_t additional_id = 0;
 
     av_log(s, AV_LOG_DEBUG, "Writing block at offset %" PRIu64 ", size %d, "
            "pts %" PRId64 ", dts %" PRId64 ", duration %d, flags %d\n",
@@ -1156,14 +1163,46 @@ static void mkv_write_block(AVFormatContext *s, AVIOContext *pb,
         offset = 8;
     }
 
-    put_ebml_id(pb, blockid);
-    put_ebml_num(pb, size+4, 0);
-    avio_w8(pb, 0x80 | (pkt->stream_index + 1));     // this assumes stream_index is less than 126
-    avio_wb16(pb, ts - mkv->cluster_pts);
-    avio_w8(pb, flags);
-    avio_write(pb, data + offset, size);
-    if (data != pkt->data)
-        av_free(data);
+    side_data = av_packet_get_side_data(pkt,
+                                        AV_PKT_DATA_MATROSKA_BLOCKADDITIONAL,
+                                        &side_data_size);
+    if (side_data) {
+        additional_id = AV_RB64(side_data);
+        side_data += 8;
+        side_data_size -= 8;
+    }
+
+    if (side_data_size && additional_id == 1) {
+        ebml_master block_group, block_additions, block_more;
+        block_group = start_ebml_master(pb, MATROSKA_ID_BLOCKGROUP, 0);
+        put_ebml_id(pb, MATROSKA_ID_BLOCK);
+        put_ebml_num(pb, size+4, 0);
+        avio_w8(pb, 0x80 | (pkt->stream_index + 1)); // track number
+        avio_wb16(pb, ts - mkv->cluster_pts);
+        avio_w8(pb, flags);
+        avio_write(pb, data + offset, size);
+        if (data != pkt->data)
+            av_free(data);
+        block_additions = start_ebml_master(pb, MATROSKA_ID_BLOCKADDITIONS, 0);
+        block_more = start_ebml_master(pb, MATROSKA_ID_BLOCKMORE, 0);
+        put_ebml_uint(pb, MATROSKA_ID_BLOCKADDID, 1);
+        put_ebml_id(pb, MATROSKA_ID_BLOCKADDITIONAL);
+        put_ebml_num(pb, side_data_size, 0);
+        avio_write(pb, side_data, side_data_size);
+        end_ebml_master(pb, block_more);
+        end_ebml_master(pb, block_additions);
+        end_ebml_master(pb, block_group);
+    }
+    else {
+        put_ebml_id(pb, blockid);
+        put_ebml_num(pb, size+4, 0);
+        avio_w8(pb, 0x80 | (pkt->stream_index + 1));     // this assumes stream_index is less than 126
+        avio_wb16(pb, ts - mkv->cluster_pts);
+        avio_w8(pb, flags);
+        avio_write(pb, data + offset, size);
+        if (data != pkt->data)
+            av_free(data);
+    }
 }
 
 static int srt_get_duration(uint8_t **buf)