flvmux: Return NEED_DATA when we drop a buffer

When we are dropping a buffer in find_best_pad (e.g. waiting for a
keyframe, or skipping backwards timestamp), return
GST_AGGREGATOR_FLOW_NEED_DATA to make sure we have enough data at the
next run. Otherwise, a stream that accidentally fell behind (e.g.
relinking race, or just waiting for a keyframe) will never get the
opportunity to catch up to the other one, because the other one will
always keep advancing.

Part-of: <https://gitlab.freedesktop.org/gstreamer/gst-plugins-good/-/merge_requests/696>

1 files changed, 30 insertions, 7 deletions

diff --git a/gst/flv/gstflvmux.c b/gst/flv/gstflvmux.c
index 564f9353e..71ecd7aeb 100644
--- a/gst/flv/gstflvmux.c
+++ b/gst/flv/gstflvmux.c
@@ -1850,7 +1850,8 @@ gst_flv_mux_rewrite_header (GstFlvMux * mux)
 /* Returns NULL, or a reference to the pad with the
  * buffer with lowest running time */
 static GstFlvMuxPad *
-gst_flv_mux_find_best_pad (GstAggregator * aggregator, GstClockTime * ts)
+gst_flv_mux_find_best_pad (GstAggregator * aggregator, GstClockTime * ts,
+    gboolean timeout)
 {
   GstFlvMuxPad *best = NULL;
   GstBuffer *buffer;
@@ -1871,8 +1872,16 @@ gst_flv_mux_find_best_pad (GstAggregator * aggregator, GstClockTime * ts)
         gint64 t = GST_CLOCK_TIME_NONE;
 
         buffer = gst_aggregator_pad_peek_buffer (apad);
-        if (!buffer)
-          continue;
+        if (!buffer) {
+          if (timeout || GST_PAD_IS_EOS (apad)) {
+            continue;
+          } else {
+            if (best)
+              gst_object_replace ((GstObject **) & best, NULL);
+            best_ts = GST_CLOCK_TIME_NONE;
+            break;
+          }
+        }
 
         if (fpad->drop_deltas) {
           if (mux->skip_backwards_streams
@@ -1881,7 +1890,14 @@ gst_flv_mux_find_best_pad (GstAggregator * aggregator, GstClockTime * ts)
                 "Dropped buffer %" GST_PTR_FORMAT " until keyframe", buffer);
             gst_buffer_unref (buffer);
             gst_aggregator_pad_drop_buffer (apad);
-            continue;
+            if (timeout) {
+              continue;
+            } else {
+              if (best)
+                gst_object_replace ((GstObject **) & best, NULL);
+              best_ts = GST_CLOCK_TIME_NONE;
+              break;
+            }
           } else {
             /* drop-deltas is set and the buffer isn't delta, drop flag */
             fpad->drop_deltas = FALSE;
@@ -1902,7 +1918,14 @@ gst_flv_mux_find_best_pad (GstAggregator * aggregator, GstClockTime * ts)
             gst_aggregator_pad_drop_buffer (apad);
             /* Look for non-delta buffer */
             fpad->drop_deltas = TRUE;
-            continue;
+            if (timeout) {
+              continue;
+            } else {
+              if (best)
+                gst_object_replace ((GstObject **) & best, NULL);
+              best_ts = GST_CLOCK_TIME_NONE;
+              break;
+            }
           }
         }
 
@@ -1958,7 +1981,7 @@ gst_flv_mux_aggregate (GstAggregator * aggregator, gboolean timeout)
       return GST_FLOW_ERROR;
     }
 
-    best = gst_flv_mux_find_best_pad (aggregator, &ts);
+    best = gst_flv_mux_find_best_pad (aggregator, &ts, timeout);
     if (!best) {
       if (!gst_flv_mux_are_all_pads_eos (mux))
         return GST_AGGREGATOR_FLOW_NEED_DATA;
@@ -1981,7 +2004,7 @@ gst_flv_mux_aggregate (GstAggregator * aggregator, gboolean timeout)
         mux->first_timestamp = 0;
     }
   } else {
-    best = gst_flv_mux_find_best_pad (aggregator, &ts);
+    best = gst_flv_mux_find_best_pad (aggregator, &ts, timeout);
   }
 
   if (mux->new_tags && mux->streamable) {