Handle case when audio converted does not return immediately

c_src/xav/reader.c

@@ -136,6 +136,7 @@ int reader_next_frame(struct Reader *reader) {
     ret = avcodec_receive_frame(reader->c, reader->frame);
 
     if (ret == 0) {
+      XAV_LOG_DEBUG("Successfully received frame");
       frame_ready = 1;
     } else if (ret == AVERROR_EOF) {
       XAV_LOG_DEBUG("EOF");

lib/reader.ex

@@ -111,11 +111,16 @@ defmodule Xav.Reader do
   Reads and decodes the next frame.
   """
   @spec next_frame(t()) :: {:ok, Xav.Frame.t()} | {:error, :eof}
-  def next_frame(%__MODULE__{reader: reader}) do
-    case Xav.Reader.NIF.next_frame(reader) do
+  def next_frame(%__MODULE__{reader: ref} = reader) do
+    case Xav.Reader.NIF.next_frame(ref) do
       {:ok, {data, format, width, height, pts}} ->
         {:ok, Xav.Frame.new(data, format, width, height, pts)}
 
+      {:ok, {"", _format, _samples, _pts}} ->
+        # Sometimes, audio converter might not return data immediately.
+        # Hence, call until we succeed.
+        next_frame(reader)
+
       {:ok, {data, format, samples, pts}} ->
         {:ok, Xav.Frame.new(data, format, samples, pts)}
 

test/reader_test.exs

@@ -43,15 +43,20 @@ defmodule Xav.ReaderTest do
 
   test "speech to text" do
     for {path, expected_output} <- [
-          # This file has been downloaded from https://audio-samples.github.io/
-          # Section: Samples from the model without biasing or priming.
           {"./test/fixtures/stt/melnet_sample_0.mp3",
            """
             My thought, I have nobody by a beauty and will as you poured. \
            Mr. Rochester has served and that so don't find a simple and \
            devoted aboud to what might in a\
            """},
           {"./test/fixtures/stt/harvard.wav",
+           """
+            The stale smell of old beer lingers. It takes heat to bring out the odor. \
+           A cold dip restores health in zest. A salt pickle tastes fine with ham. \
+           Tacos all pastora are my favorite. A zestful food is the hot cross bun.\
+           """},
+          # This mp3 file results in an empty buffer after first conversion.
+          {"./test/fixtures/stt/harvard.mp3",
            """
             The stale smell of old beer lingers. It takes heat to bring out the odor. \
            A cold dip restores health in zest. A salt pickle tastes fine with ham. \