Expose the duration field for frames

Signed-off-by: Max Ehrlich <max.ehr@gmail.com>

Author: Queuecumber

av/frame.pyi

@@ -9,6 +9,7 @@ class SideData(TypedDict, total=False):
 class Frame:
     dts: int | None
     pts: int | None
+    duration: int | None
     time_base: Fraction
     side_data: SideData
     opaque: object

av/frame.pyx

@@ -53,6 +53,9 @@ cdef class Frame:
         if self.ptr.pts != lib.AV_NOPTS_VALUE:
             self.ptr.pts = lib.av_rescale_q(self.ptr.pts, self._time_base, dst)
 
+        if self.ptr.duration != 0:
+            self.ptr.duration = lib.av_rescale_q(self.ptr.duration, self._time_base, dst)
+
         self._time_base = dst
 
     @property
@@ -95,6 +98,24 @@ cdef class Frame:
         else:
             self.ptr.pts = value
 
+    @property
+    def duration(self):
+        """
+        The duration of the frame in :attr:`time_base` units
+
+        :type: int
+        """
+        if self.ptr.duration == 0:
+            return None
+        return self.ptr.duration
+
+    @duration.setter
+    def duration(self, value):
+        if value is None:
+            self.ptr.duration = 0
+        else:
+            self.ptr.duration = value
+
     @property
     def time(self):
         """

av/video/frame.pyi

@@ -30,6 +30,7 @@ class PictureType(IntEnum):
 class VideoFrame(Frame):
     format: VideoFormat
     pts: int
+    duration: int
     planes: tuple[VideoPlane, ...]
     pict_type: int
     colorspace: int

include/libavcodec/avcodec.pxd

@@ -461,6 +461,8 @@ cdef extern from "libavcodec/avcodec.h" nogil:
         AVColorTransferCharacteristic color_trc
         AVColorSpace colorspace
 
+        int64_t duration
+
     cdef AVFrame* avcodec_alloc_frame()
 
     cdef struct AVPacket:

tests/test_videoframe.py

@@ -49,6 +49,23 @@ def test_opaque() -> None:
                 assert type(frame.opaque) is tuple and len(frame.opaque) == 2
 
 
+def test_frame_duration_matches_packet() -> None:
+    with av.open(fate_suite("h264/interlaced_crop.mp4")) as container:
+        packet_durations = []
+        frame_durations = []
+        for packet in container.demux():
+            if packet.pts is not None:
+                packet_durations.append((packet.pts, packet.duration))
+            for frame in packet.decode():
+                if frame.pts is not None:
+                    frame_durations.append((frame.pts, frame.duration))
+
+        packet_durations.sort(key=lambda x: x[0])
+        frame_durations.sort(key=lambda x: x[0])
+
+        assert all(pd[1] == fd[1] for pd, fd in zip(packet_durations, frame_durations))
+
+
 def test_invalid_pixel_format() -> None:
     with pytest.raises(ValueError, match="not a pixel format: '__unknown_pix_fmt'"):
         VideoFrame(640, 480, "__unknown_pix_fmt")