def _get_frames(
self, video_reader: decord.VideoReader, offset: int,
) -> List[np.ndarray]:
""" Get frames at sample length.
Args:
video_reader: the decord tool for parsing videos
offset: where to start the reader from
Returns
Frames at sample length in a List
"""
clip = list()
# decord.seek() seems to have a bug. use seek_accurate().
video_reader.seek_accurate(offset)
# first frame
clip.append(video_reader.next().asnumpy())
# remaining frames
try:
for i in range(self.sample_length - 1):
step = (
randint(self.sample_step + 1)
if self.temporal_jitter
else self.sample_step
)
if step == 0 and self.temporal_jitter:
clip.append(clip[-1].copy())
else:
if step > 1:
video_reader.skip_frames(step - 1)
cur_frame = video_reader.next().asnumpy()
clip.append(cur_frame)
except StopIteration:
# pass when video has ended
pass
# if clip needs more frames, simply duplicate the last frame in the clip.
while len(clip) < self.sample_length:
clip.append(clip[-1].copy())
return clip
shuffle=1)
ex = vl.next()
vr = VideoReader(path, ctx=cpu(0))
# a file like object works as well, for in-memory decoding
with open(path, 'rb') as f:
vr = VideoReader(f, ctx=cpu(0))
print('video frames:', len(vr))
# 1. the simplest way is to directly access frames
for i in range(len(vr)):
# the video reader will handle seeking and skipping in the most efficient manner
frame = vr[i]
print(frame.shape)
# To get multiple frames at once, use get_batch
# this is the efficient way to obtain a long list of frames
frames = vr.get_batch([1, 3, 5, 7, 9])
print(frames.shape)
# (5, 240, 320, 3)
# duplicate frame indices will be accepted and handled internally to avoid duplicate decoding
frames2 = vr.get_batch([1, 2, 3, 2, 3, 4, 3, 4, 5])
print(frames2.shape)
# (9, 240, 320, 3)
# 2. you can do cv2 style reading as well
# skip 100 frames
vr.skip_frames(100)
# seek to start
vr.seek(0)
batch = vr.next()
print('frame shape:', batch.shape)
