#include "tagspriv.h" inttagopus(Tagctx *ctx){	char *v;	uint8_t *d, h[4];	int sz, numtags, i, npages, pgend; 	d = (uint8_t*)ctx->buf;	for(npages = pgend = 0; npages < 2; npages++){		int nsegs;		if(ctx->read(ctx, d, 27) != 27)			return -1;		if(memcmp(d, "OggS", 4) != 0)			return -1; 		/* calculate the size of the packet */		nsegs = d[26];		if(nsegs > ctx->bufsz-8 || ctx->read(ctx, d, nsegs+8) != nsegs+8)			return -1;		for(sz = i = 0; i < nsegs; sz += d[i++]); 		if(memcmp(&d[nsegs], "OpusHead", 8) == 0){			if(ctx->read(ctx, d, 8) != 8 || d[0] != 1)				return -1;			sz -= 8;			ctx->channels = d[1];			ctx->samplerate = leuint(&d[4]);		}else if(memcmp(&d[nsegs], "OpusTags", 8) == 0){			/* FIXME - embedded pics make tags span multiple packets */			pgend = ctx->seek(ctx, 0, 1) + sz;			break;		} 		ctx->seek(ctx, sz-8, 1);	} 	if(npages < 3){		if(ctx->read(ctx, d, 4) != 4)			return -1;		sz = leuint(d);		if(ctx->seek(ctx, sz, 1) < 0 || ctx->read(ctx, h, 4) != 4)			return -1;		numtags = leuint(h); 		for(i = 0; i < numtags; i++){			if(ctx->read(ctx, h, 4) != 4)				return -1;			if((sz = leuint(h)) < 0)				return -1;			/* FIXME - embedded pics make tags span multiple packets */			if(pgend < ctx->seek(ctx, 0, 1)+sz)				break; 			if(sz > ctx->bufsz-1){				if(ctx->seek(ctx, sz, 1) < 0)					return -1;				continue;			}			if(ctx->read(ctx, ctx->buf, sz) != sz)				return -1;			ctx->buf[sz] = 0; 			if((v = strchr(ctx->buf, '=')) == nil)				return -1;			*v++ = 0;			cbvorbiscomment(ctx, ctx->buf, v);		}	} 	/* calculate the duration */	if(ctx->samplerate > 0){		sz = ctx->bufsz <= 4096 ? ctx->bufsz : 4096;		for(i = sz; i < 65536+16; i += sz - 16){			if(ctx->seek(ctx, -i, 2) <= 0)				break;			v = ctx->buf;			if(ctx->read(ctx, v, sz) != sz)				break;			for(; v != nil && v < ctx->buf+sz;){				v = memchr(v, 'O', ctx->buf+sz - v - 14);				if(v != nil && v[1] == 'g' && v[2] == 'g' && v[3] == 'S'){					uint64_t g = leuint(v+6) | (uint64_t)leuint(v+10)<<32;					ctx->duration = g * 1000 / 48000; /* granule positions are always 48KHz */				}				if(v != nil)					v++;			}			if(ctx->duration != 0)				break;		}	} 	return 0;}