Improve latency by waiting for the next keyframe

Instead of caching all the data from the previous keyframe till right now and
sending it to the client in a burst, since latency is important, we instead wait
for the next keyframe before sending buffers to the clients. This will lead to
a delay of upto 128 frames before the stream starts.

The keyframe distance and hence the delay can be tweaked by setting the
"keyframe-max-dist" property on vp8enc in src/encode.c:create_webm_profile()

1 files changed, 12 insertions, 18 deletions

diff --git a/src/main.c b/src/main.c
index 6e61c3e..fe9d44a 100644
--- a/src/main.c
+++ b/src/main.c
@@ -134,6 +134,15 @@ invoke_write_client_chunk (TranscodeClientCtx *ctx)
   }
 
   buffer = gst_sample_get_buffer (sample);
+
+  /* Skip all frames till the next keyframe */
+  if (!ctx->keyframe_found &&
+      GST_BUFFER_FLAG_IS_SET (buffer, GST_BUFFER_FLAG_DELTA_UNIT)) {
+    gst_sample_unref (sample);
+    return FALSE;
+  }
+  ctx->keyframe_found = TRUE;
+
   gst_buffer_map (buffer, &info, GST_MAP_READ);
 
   soup_message_body_append (ctx->msg->response_body, SOUP_MEMORY_COPY,
@@ -151,7 +160,7 @@ static GstFlowReturn
 write_client_chunk_cb (GstElement         *appsink,
                        TranscodeClientCtx *ctx)
 {
-  g_main_context_invoke_full (NULL, G_PRIORITY_HIGH,
+  g_main_context_invoke_full (NULL, G_PRIORITY_DEFAULT,
                               (GSourceFunc)invoke_write_client_chunk,
                               ctx, NULL);
   return GST_FLOW_OK;
@@ -227,7 +236,6 @@ GET:
     /* A GET request was received. We connect from the pipeline to the
      * client requesting the stream and start writing the response. */
     GstCaps *caps = NULL;
-    GstState state;
     GstBuffer *buffer;
     GstFlowReturn ret;
     GstStateChangeReturn state_change;
@@ -311,7 +319,7 @@ GET:
     buffer = stp_get_streamheader_from_caps (caps);
     if (!buffer) {
       g_critical ("Unable to get streamheader from caps");
-      goto push_keyframe;
+      goto nostreamheader;
     }
 
     ret = gst_pad_push (srcpad, buffer);
@@ -321,21 +329,7 @@ GET:
       goto err;
     }
 
-push_keyframe:
-    ret = gst_pad_push_list (srcpad,
-                             gst_buffer_list_copy (server_ctx->keyframe));
-    if (ret != GST_FLOW_OK) {
-      g_critical ("Unable to push keyframe data: %s",
-                  gst_flow_get_name (ret));
-      goto err;
-    }
-
-    state_change = gst_element_get_state (server_ctx->pipeline,
-                                          &state, NULL, 1);
-    g_debug ("Pushed buffer. State was %s:%s.",
-             gst_element_state_change_return_get_name (state_change),
-             gst_element_state_get_name (state));
-
+nostreamheader:
     client_ctx->appsink = appsink;
 
     g_signal_connect (appsink, "new-sample",