From fae29cb3c21ffe480f110c2f9448a60c871e39fd Mon Sep 17 00:00:00 2001
From: Jan Schmidt <jan@centricular.com>
Date: Fri, 19 Mar 2021 02:51:20 +1100
Subject: [PATCH] qtmux: Protect against writing absurd sample durations

If the input DTS goes backward or is missing, the calculated
sample duration goes negative and wraps around to a very big
number. In that case, just write a sample with a duration of
0 and hope the problem is transient.

Part-of: <https://gitlab.freedesktop.org/gstreamer/gst-plugins-good/-/merge_requests/914>
---
 gst/isomp4/gstqtmux.c | 23 +++++++++++++++++------
 gst/isomp4/gstqtmux.h |  4 ++++
 2 files changed, 21 insertions(+), 6 deletions(-)

diff --git a/gst/isomp4/gstqtmux.c b/gst/isomp4/gstqtmux.c
index 821e7f1710..a4d949c0c3 100644
--- a/gst/isomp4/gstqtmux.c
+++ b/gst/isomp4/gstqtmux.c
@@ -658,6 +658,7 @@ gst_qt_mux_pad_reset (GstQTMuxPad * qtpad)
   qtpad->sparse = FALSE;
   qtpad->first_cc_sample_size = 0;
   qtpad->flow_status = GST_FLOW_OK;
+  qtpad->warned_empty_duration = FALSE;
 
   gst_buffer_replace (&qtpad->last_buf, NULL);
 
@@ -5150,18 +5151,28 @@ gst_qt_mux_add_buffer (GstQTMux * qtmux, GstQTMuxPad * pad, GstBuffer * buf)
   /* duration actually means time delta between samples, so we calculate
    * the duration based on the difference in DTS or PTS, falling back
    * to DURATION if the other two don't exist, such as with the last
-   * sample before EOS. Or use 0 if nothing else is available */
+   * sample before EOS. Or use 0 if nothing else is available,
+   * making sure that duration doesn't go negative and wraparound. */
   if (GST_BUFFER_DURATION_IS_VALID (last_buf))
     duration = GST_BUFFER_DURATION (last_buf);
   else
     duration = 0;
   if (!pad->sparse) {
     if (buf && GST_BUFFER_DTS_IS_VALID (buf)
-        && GST_BUFFER_DTS_IS_VALID (last_buf))
-      duration = GST_BUFFER_DTS (buf) - GST_BUFFER_DTS (last_buf);
-    else if (buf && GST_BUFFER_PTS_IS_VALID (buf)
-        && GST_BUFFER_PTS_IS_VALID (last_buf))
-      duration = GST_BUFFER_PTS (buf) - GST_BUFFER_PTS (last_buf);
+        && GST_BUFFER_DTS_IS_VALID (last_buf)) {
+      if (GST_BUFFER_DTS (buf) >= GST_BUFFER_DTS (last_buf))
+        duration = GST_BUFFER_DTS (buf) - GST_BUFFER_DTS (last_buf);
+    } else if (buf && GST_BUFFER_PTS_IS_VALID (buf)
+        && GST_BUFFER_PTS_IS_VALID (last_buf)) {
+      if (GST_BUFFER_PTS (buf) >= GST_BUFFER_PTS (last_buf))
+        duration = GST_BUFFER_PTS (buf) - GST_BUFFER_PTS (last_buf);
+    }
+    if (duration == 0 && !pad->warned_empty_duration) {
+      GST_WARNING_OBJECT (qtmux,
+          "Sample with zero duration on pad %" GST_PTR_FORMAT
+          " due to missing or backward timestamps on the input stream", pad);
+      pad->warned_empty_duration = TRUE;
+    }
   }
 
   if (qtmux->current_pad != pad || qtmux->current_chunk_offset == -1) {
diff --git a/gst/isomp4/gstqtmux.h b/gst/isomp4/gstqtmux.h
index f4038852a9..0e6e7f6793 100644
--- a/gst/isomp4/gstqtmux.h
+++ b/gst/isomp4/gstqtmux.h
@@ -128,6 +128,10 @@ struct _GstQTMuxPad
   GstClockTime last_dts;
   guint64 sample_offset;
 
+  /* TRUE if we saw backward/missing DTS on this
+   * pad (and warned about it */
+  gboolean warned_empty_duration;
+
   /* This is compensate for CTTS */
   GstClockTime dts_adjustment;