Put back more stuff (fix)

Author: NicolasHug

torchvision/io/video.py

@@ -47,6 +47,11 @@ def _check_av_available() -> None:
 def _av_available() -> bool:
     return not isinstance(av, Exception)
 
+# PyAV has some reference cycles
+_CALLED_TIMES = 0
+_GC_COLLECTION_INTERVAL = 10
+
+
 def write_video(
     filename: str,
     video_array: torch.Tensor,
@@ -167,6 +172,85 @@ def write_video(
         for packet in stream.encode():
             container.mux(packet)
 
+def _read_from_stream(
+    container: "av.container.Container",
+    start_offset: float,
+    end_offset: float,
+    pts_unit: str,
+    stream: "av.stream.Stream",
+    stream_name: dict[str, Optional[Union[int, tuple[int, ...], list[int]]]],
+) -> list["av.frame.Frame"]:
+    global _CALLED_TIMES, _GC_COLLECTION_INTERVAL
+    _CALLED_TIMES += 1
+    if _CALLED_TIMES % _GC_COLLECTION_INTERVAL == _GC_COLLECTION_INTERVAL - 1:
+        gc.collect()
+
+    if pts_unit == "sec":
+        # TODO: we should change all of this from ground up to simply take
+        # sec and convert to MS in C++
+        start_offset = int(math.floor(start_offset * (1 / stream.time_base)))
+        if end_offset != float("inf"):
+            end_offset = int(math.ceil(end_offset * (1 / stream.time_base)))
+    else:
+        warnings.warn("The pts_unit 'pts' gives wrong results. Please use pts_unit 'sec'.")
+
+    frames = {}
+    should_buffer = True
+    max_buffer_size = 5
+    if stream.type == "video":
+        # DivX-style packed B-frames can have out-of-order pts (2 frames in a single pkt)
+        # so need to buffer some extra frames to sort everything
+        # properly
+        extradata = stream.codec_context.extradata
+        # overly complicated way of finding if `divx_packed` is set, following
+        # https://github.com/FFmpeg/FFmpeg/commit/d5a21172283572af587b3d939eba0091484d3263
+        if extradata and b"DivX" in extradata:
+            # can't use regex directly because of some weird characters sometimes...
+            pos = extradata.find(b"DivX")
+            d = extradata[pos:]
+            o = re.search(rb"DivX(\d+)Build(\d+)(\w)", d)
+            if o is None:
+                o = re.search(rb"DivX(\d+)b(\d+)(\w)", d)
+            if o is not None:
+                should_buffer = o.group(3) == b"p"
+    seek_offset = start_offset
+    # some files don't seek to the right location, so better be safe here
+    seek_offset = max(seek_offset - 1, 0)
+    if should_buffer:
+        # FIXME this is kind of a hack, but we will jump to the previous keyframe
+        # so this will be safe
+        seek_offset = max(seek_offset - max_buffer_size, 0)
+    try:
+        # TODO check if stream needs to always be the video stream here or not
+        container.seek(seek_offset, any_frame=False, backward=True, stream=stream)
+    except FFmpegError:
+        # TODO add some warnings in this case
+        # print("Corrupted file?", container.name)
+        return []
+    buffer_count = 0
+    try:
+        for _idx, frame in enumerate(container.decode(**stream_name)):
+            frames[frame.pts] = frame
+            if frame.pts >= end_offset:
+                if should_buffer and buffer_count < max_buffer_size:
+                    buffer_count += 1
+                    continue
+                break
+    except FFmpegError:
+        # TODO add a warning
+        pass
+    # ensure that the results are sorted wrt the pts
+    result = [frames[i] for i in sorted(frames) if start_offset <= frames[i].pts <= end_offset]
+    if len(frames) > 0 and start_offset > 0 and start_offset not in frames:
+        # if there is no frame that exactly matches the pts of start_offset
+        # add the last frame smaller than start_offset, to guarantee that
+        # we will have all the necessary data. This is most useful for audio
+        preceding_frames = [i for i in frames if i < start_offset]
+        if len(preceding_frames) > 0:
+            first_frame_pts = max(preceding_frames)
+            result.insert(0, frames[first_frame_pts])
+    return result
+
 
 def read_video(
     filename: str,