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matroska: ogg: set Theora granule position according to the spec

--- a/ogg.c

+++ b/ogg.c

@@ -13,6 +13,14 @@

 	u32int crc;

 	int psz, i, n, ntot, ip;

+	if(ctx->frid == 0 && ctx->fmt == FmtTheora && np > 0 && p->sz > 41){

+		if(memcmp(p->data, "\x80theora", 7) != 0){

+			werrstr("invalid Theora packet");

+			return -1;

+		}

+		ctx->kfgshift = ((p->data[40]<<8 | p->data[41]) >> 5) & 0x1f;

+	}

+

 	h[5] = htype;

 	h[6] = granule;

 	h[7] = granule >> 8;

@@ -131,7 +139,12 @@

 	}

 	if(ctx->fmt == FmtTheora){

-		gr = 0;

+		ctx->nonkey++; /* FIXME VREV 1 vs 0 diff here, to make it work with 0 */

+		if(key){

+			ctx->key += ctx->nonkey;

+			ctx->nonkey = 0;

+		}

+		gr = (uvlong)ctx->key<<ctx->kfgshift | ctx->nonkey;

 	}else{

 		gr = (ts * 48) / 1000000;

 	}

--- a/packet.h

+++ b/packet.h

@@ -30,8 +30,6 @@

 	u32int trackuid;

 	u32int fmt;

-	int key;

-

 	struct {

 		int width;

 		int height;

@@ -50,6 +48,9 @@

 		int n;

 	}ps[16];

 	int nps;

+	int key;

+	int nonkey;

+	int kfgshift;

 };

 int aacpacket(Biobuf *out, Packetctx *ctx, Packet *p, int np, uvlong ts, int key);