prevent repeating frame indices (fixes: #1158)

av/codec/context.pxd

@@ -43,6 +43,7 @@ cdef class CodecContext:
     cdef _prepare_and_time_rebase_frames_for_encode(self, Frame frame)
     cdef _prepare_frames_for_encode(self, Frame frame)
     cdef _setup_encoded_packet(self, Packet)
+    cdef _correct_frame_indices(self, frame_list)
     cdef _setup_decoded_frame(self, Frame, Packet)
 
     # Implemented by base for the generic send/recv API.

av/codec/context.pyx

@@ -513,24 +513,34 @@ cdef class CodecContext:
 
         self.open(strict=False)
 
-        res = []
+        frame_list = []
         for frame in self._send_packet_and_recv(packet):
             if isinstance(frame, Frame):
                 self._setup_decoded_frame(frame, packet)
-            res.append(frame)
-        return res
+            frame_list.append(frame)
+        if packet and packet.stream and packet.stream.type != "subtitle":
+            self._correct_frame_indices(frame_list)
+        return frame_list
 
-    cdef _setup_decoded_frame(self, Frame frame, Packet packet):
+    cdef _correct_frame_indices(self, frame_list):
+        """
+        All frames in the list returned by '_send_packet_and_recv' will have the same index.
+        This will set the correct indices.
+        """
+        cdef Frame frame
+        correction = len(frame_list)
+        for frame in frame_list:
+            frame.index = self.ptr.frame_num - correction
+            correction -= 1
 
+    cdef _setup_decoded_frame(self, Frame frame, Packet packet):
         # Propagate our manual times.
         # While decoding, frame times are in stream time_base, which PyAV
         # is carrying around.
         # TODO: Somehow get this from the stream so we can not pass the
         # packet here (because flushing packets are bogus).
         frame._time_base = packet._time_base
 
-        frame.index = self.ptr.frame_number - 1
-
     property name:
         def __get__(self):
             return self.codec.name

include/libavcodec/avcodec.pxd

@@ -171,7 +171,7 @@ cdef extern from "libavcodec/avcodec.h" nogil:
         int global_quality
         int compression_level
 
-        int frame_number
+        int frame_num
 
         int qmin
         int qmax

tests/test_decode.py

@@ -124,3 +124,22 @@ def test_decode_close_then_use(self):
                     getattr(container, attr)
                 except AssertionError:
                     pass
+
+    def test_decode_frame_indices(self):
+        for thread_type in ("NONE", "AUTO"):
+            for thread_count in range(4):
+                for skip_type in ("NONE", "NONKEY"):
+                    frame_list = []
+                    compare_list = []
+                    frame_count = 0
+                    with av.open(fate_suite("h264/interlaced_crop.mp4")) as container:
+                        stream = container.streams.video[0]
+                        stream.thread_type = thread_type
+                        stream.thread_count = thread_count
+                        stream.codec_context.skip_frame = skip_type
+                        for packet in container.demux(stream):
+                            for frame in packet.decode():
+                                frame_list.append(frame.index)
+                                compare_list.append(frame_count)
+                                frame_count += 1
+                    self.assertEqual(frame_list, compare_list)