mpegtspacketizer: memcmp potentially seen_before data

Theoretically the version number is incremented every time there's a new
section, but in a world of streaming we can't easily make that
assumption.

An example of a broken use case is when we're cat-ing two mpeg-ts files
together, which is equivalent of capturing a DVB stream while switching
channels. A set-top box would know that we switched the channels and
reset the demuxer, but in practice this might not happen.

Part-of: <https://gitlab.freedesktop.org/gstreamer/gst-plugins-bad/-/merge_requests/2468>

diff --git a/gst/mpegtsdemux/mpegtspacketizer.c b/gst/mpegtsdemux/mpegtspacketizer.c
index 4e961fe..fe9ff2e 100644 (file)
--- a/gst/mpegtsdemux/mpegtspacketizer.c
+++ b/gst/mpegtsdemux/mpegtspacketizer.c
@@ -157,7 +157,7 @@ find_subtable (GSList * subtables, guint8 table_id, guint16 subtable_extension)
 static gboolean
 seen_section_before (MpegTSPacketizerStream * stream, guint8 table_id,
     guint16 subtable_extension, guint8 version_number, guint8 section_number,
-    guint8 last_section_number)
+    guint8 last_section_number, guint8 * data_start, gsize to_read)
 {
   MpegTSPacketizerStreamSubtable *subtable;
 
@@ -178,7 +178,17 @@ seen_section_before (MpegTSPacketizerStream * stream, guint8 table_id,
     return FALSE;
   }
   /* Finally return whether we saw that section or not */
-  return MPEGTS_BIT_IS_SET (subtable->seen_section, section_number);
+  if (!MPEGTS_BIT_IS_SET (subtable->seen_section, section_number)) {
+    GST_DEBUG ("Different section_number");
+    return FALSE;
+  }
+
+  if (stream->section_data) {
+    /* Everything else is the same, fall back to memcmp */
+    return (memcmp (stream->section_data, data_start, to_read) != 0);
+  }
+
+  return FALSE;
 }
 
 static MpegTSPacketizerStreamSubtable *
@@ -1192,7 +1202,8 @@ section_start:
    * * same section_number was seen
    */
   if (seen_section_before (stream, table_id, subtable_extension,
-          version_number, section_number, last_section_number)) {
+          version_number, section_number, last_section_number, data_start,
+          to_read)) {
     GST_DEBUG
         ("PID 0x%04x Already processed table_id:0x%02x subtable_extension:0x%04x, version_number:%d, section_number:%d",
         packet->pid, table_id, subtable_extension, version_number,