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matroska, aac: construct ADTS from codec private data

--- a/aac.c

+++ b/aac.c

@@ -7,11 +7,39 @@

 int

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

 {

-	int i;

+	int i, chanc, ratei, objt, sz;

+	u16int x;

 	USED(ts);

+	if(ctx->frid == 0){ /* set up ADTS */

+		if(ctx->codec.priv.sz < 2){

+			/* FIXME we could reconstruct it from codec mapping and Audio element */

+			werrstr("no codec private data to construct ADTS");

+			return -1;

+		}

+		x = ctx->codec.priv.data[0]<<8 | ctx->codec.priv.data[1];

+		chanc = (x>>3) & 0xf;

+		ratei = (x>>7) & 0xf;

+		objt = x>>11;

+		if(objt > 4){

+			werrstr("AAC object type %d, can't write ADTS", objt);

+			return -1;

+		}

+		sz = 0; /* will be filled in later */

+		ctx->adts[0] = 0xff; /* syncword */

+		ctx->adts[1] = 0xf1; /* syncword, mpeg4, no crc */

+		ctx->adts[2] = (objt-1)<<6 | ratei<<2 | chanc>>2; /* object type, rate, channel config */

+		ctx->adts[3] = (chanc&3)<<6 | (sz>>11)&3; /* channel config, frame length */

+		ctx->adts[4] = sz>>3; /* frame length */

+		ctx->adts[5] = (sz&7)<<5 | 0x1f; /* frame length, fullness */

+		ctx->adts[6] = 0xfc; /* fullness, number of frames */

+	}

 	for(i = 0; i < np; i++, p++){

-		if(Bwrite(out, p->data, p->sz) != p->sz)

+		sz = 7+p->sz;

+		ctx->adts[3] = ctx->adts[3]&~3 | (sz>>11)&3; /* channels, frame length */

+		ctx->adts[4] = sz>>3; /* frame length */

+		ctx->adts[5] = (sz&7)<<5 | 0x1f; /* frame length, fullness */

+		if(Bwrite(out, ctx->adts, 7) != 7 || Bwrite(out, p->data, p->sz) != p->sz)

 			goto err;

 	}

 	ctx->frid++;

--- a/ogg.c

+++ b/ogg.c

@@ -90,7 +90,7 @@

 		dsz = ctx->codec.priv.sz;

 		/* id/codec setup header always goes first */

-		if(ctx->codec.priv.sz > 0){ /* if we have codec setup data, write it */

+		if(dsz > 0){ /* if we have codec setup data, write it */

 			if(ctx->fmt == FmtVorbis || ctx->fmt == FmtTheora){

 				i = *d++;

 				dsz--;

--- a/packet.h

+++ b/packet.h

@@ -39,6 +39,7 @@

 		int channels;

 		int bps;

 	}audio;

+	uchar adts[7];

 };

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