avidemux: Drop video frames up to the desired keyframe after a seek

The audio packets in AVI are generally muxed ~0.5s before the
corresponding video packet. This changes causes downstream to only
receive packets with roughly corresponding timestamps.

gst/avi/gstavidemux.c

@@ -4191,7 +4191,7 @@ avi_demux_handle_seek_push (GstAviDemux * avi, GstPad * pad, GstEvent * event)
   /* re-use cur to be the timestamp of the seek as it _will_ be */
   cur = stream->current_timestamp;
 
-  min_offset = stream->index[index].offset;
+  min_offset = avi->seek_kf_offset = stream->index[index].offset;
 
   GST_DEBUG_OBJECT (avi,
       "Seek to: ts %" GST_TIME_FORMAT " (on str %u, idx %u, offset %"
@@ -4838,15 +4838,28 @@ gst_avi_demux_stream_data (GstAviDemux * avi)
     } else {
       GstAviStream *stream;
       GstClockTime next_ts = 0;
-      GstBuffer *buf;
+      GstBuffer *buf = NULL;
       guint64 offset;
+      gboolean saw_desired_kf = stream_nr != avi->main_stream
+          || avi->offset >= avi->seek_kf_offset;
 
+      if (stream_nr == avi->main_stream && avi->offset == avi->seek_kf_offset) {
+        GST_DEBUG_OBJECT (avi, "Desired keyframe reached");
+        avi->seek_kf_offset = 0;
+      }
+
+      if (saw_desired_kf) {
         gst_adapter_flush (avi->adapter, 8);
-
         /* get buffer */
         buf = gst_adapter_take_buffer (avi->adapter, GST_ROUND_UP_2 (size));
         /* patch the size */
         GST_BUFFER_SIZE (buf) = size;
+      } else {
+        GST_DEBUG_OBJECT (avi,
+            "Desired keyframe not yet reached, flushing chunk");
+        gst_adapter_flush (avi->adapter, 8 + GST_ROUND_UP_2 (size));
+      }
+
       offset = avi->offset;
       avi->offset += 8 + GST_ROUND_UP_2 (size);
 
@@ -4862,10 +4875,9 @@ gst_avi_demux_stream_data (GstAviDemux * avi)
       if (G_UNLIKELY (!stream->pad)) {
         GST_WARNING_OBJECT (avi, "no pad for stream ID %" GST_FOURCC_FORMAT,
             GST_FOURCC_ARGS (tag));
+        if (buf)
           gst_buffer_unref (buf);
       } else {
-        GstClockTime dur_ts = 0;
-
         /* get time of this buffer */
         gst_pad_query_position (stream->pad, &format, (gint64 *) & next_ts);
         if (G_UNLIKELY (format != GST_FORMAT_TIME))
@@ -4877,6 +4889,12 @@ gst_avi_demux_stream_data (GstAviDemux * avi)
         stream->current_entry++;
         stream->current_total += size;
 
+        /* update current position in the segment */
+        gst_segment_set_last_stop (&avi->segment, GST_FORMAT_TIME, next_ts);
+
+        if (saw_desired_kf && buf) {
+          GstClockTime dur_ts = 0;
+
           /* invert the picture if needed */
           buf = gst_avi_demux_invert (stream, buf);
 
@@ -4899,11 +4917,8 @@ gst_avi_demux_stream_data (GstAviDemux * avi)
               "Pushing buffer with time=%" GST_TIME_FORMAT ", duration %"
               GST_TIME_FORMAT ", offset %" G_GUINT64_FORMAT
               " and size %d over pad %s", GST_TIME_ARGS (next_ts),
-            GST_TIME_ARGS (GST_BUFFER_DURATION (buf)), GST_BUFFER_OFFSET (buf),
+              GST_TIME_ARGS (GST_BUFFER_DURATION (buf)),
-            size, GST_PAD_NAME (stream->pad));
+              GST_BUFFER_OFFSET (buf), size, GST_PAD_NAME (stream->pad));
-
-        /* update current position in the segment */
-        gst_segment_set_last_stop (&avi->segment, GST_FORMAT_TIME, next_ts);
 
           /* mark discont when pending */
           if (G_UNLIKELY (stream->discont)) {
@@ -4922,6 +4937,7 @@ gst_avi_demux_stream_data (GstAviDemux * avi)
         }
       }
     }
+  }
 
 done:
   return res;

gst/avi/gstavidemux.h

@@ -199,6 +199,8 @@ typedef struct _GstAviDemux {
   guint          odml_stream;
   guint          odml_subidx;
   guint64       *odml_subidxs;
+
+  guint64        seek_kf_offset; /* offset of the keyframe to which we want to seek */
 } GstAviDemux;
 
 typedef struct _GstAviDemuxClass {