flacdec: fix issues with large metadata blocks when streaming unframed flac

Parse metadata blocks when handling unparsed flac in push mode. This
works around a bunch of issues with the flac decoder when handling
metadata blocks that are larger than the max. flac framesize, which
coverart blocks often are. We need to have all the data for these
blocks available when we pass data to libflac.

http://gstreamer-devel.966125.n4.nabble.com/Flac-files-that-will-playback-but-not-stream-td3338198.html#a3395276

https://bugzilla.gnome.org/show_bug.cgi?id=566769

ext/flac/gstflacdec.c

@@ -1304,6 +1304,53 @@ gst_flac_dec_sink_event (GstPad * pad, GstEvent * event)
   return res;
 }
 
+static gboolean
+gst_flac_dec_chain_parse_headers (GstFlacDec * dec)
+{
+  guint8 marker[4];
+  guint avail, off;
+
+  avail = gst_adapter_available (dec->adapter);
+  if (avail < 4)
+    return FALSE;
+
+  gst_adapter_copy (dec->adapter, marker, 0, 4);
+  if (strncmp ((const gchar *) marker, "fLaC", 4) != 0) {
+    GST_ERROR_OBJECT (dec, "Unexpected header, expected fLaC header");
+    return TRUE;                /* abort header parsing */
+  }
+
+  GST_DEBUG_OBJECT (dec, "fLaC header          : len           4 @ %7u", 0);
+
+  off = 4;
+  while (avail > (off + 1 + 3)) {
+    gboolean is_last;
+    guint8 mb_hdr[4];
+    guint len, block_type;
+
+    gst_adapter_copy (dec->adapter, mb_hdr, off, 4);
+
+    is_last = ((mb_hdr[0] & 0x80) == 0x80);
+    block_type = mb_hdr[0] & 0x7f;
+    len = GST_READ_UINT24_BE (mb_hdr + 1);
+    GST_DEBUG_OBJECT (dec, "Metadata block type %u: len %7u + 4 @ %7u%s",
+        block_type, len, off, (is_last) ? " (last)" : "");
+    off += 4 + len;
+
+    if (is_last)
+      break;
+
+    if (off >= avail) {
+      GST_LOG_OBJECT (dec, "Need more data: next offset %u > avail %u", off,
+          avail);
+      return FALSE;
+    }
+  }
+
+  /* want metadata blocks plus at least one frame */
+  return (off + FLAC__MAX_BLOCK_SIZE >= avail);
+}
+
 static GstFlowReturn
 gst_flac_dec_chain (GstPad * pad, GstBuffer * buf)
 {
@@ -1368,6 +1415,15 @@ gst_flac_dec_chain (GstPad * pad, GstBuffer * buf)
   dec->last_flow = GST_FLOW_OK;
 
   if (!dec->framed) {
+    if (G_UNLIKELY (!dec->got_headers)) {
+      if (!gst_flac_dec_chain_parse_headers (dec)) {
+        GST_LOG_OBJECT (dec, "don't have metadata blocks yet, need more data");
+        goto out;
+      }
+      GST_INFO_OBJECT (dec, "have all metadata blocks now");
+      dec->got_headers = TRUE;
+    }
+
     /* wait until we have at least 64kB because libflac's StreamDecoder
      * interface is a bit dumb it seems (if we don't have as much data as
      * it wants it will call our read callback repeatedly and the only
@@ -1403,6 +1459,8 @@ gst_flac_dec_chain (GstPad * pad, GstBuffer * buf)
     GST_DEBUG_OBJECT (dec, "don't have all headers yet");
   }
 
+out:
+
   return dec->last_flow;
 }
 
@@ -1992,6 +2050,7 @@ gst_flac_dec_sink_activate_push (GstPad * sinkpad, gboolean active)
   if (active) {
     gst_flac_dec_setup_decoder (dec);
     dec->streaming = TRUE;
+    dec->got_headers = FALSE;
   }
   return TRUE;
 }

ext/flac/gstflacdec.h

@@ -48,6 +48,8 @@ struct _GstFlacDec {
   gboolean                     framed;
   gboolean                     streaming;
 
+  gboolean       got_headers; /* if we've parsed the headers (unframed push mode only) */
+
   GstPad        *sinkpad;
   GstPad        *srcpad;