Error with no data at frame xx always appears while set sample_rate > 1

[LiunxPaisley]

My sovlver file is like this:

name: "C3D-UCF101Net"
layer {
  name: "data"
  type: "VideoData"
  top: "data"
  top: "label"
  include {
    phase: TRAIN
  }
  transform_param {
    crop_size: 112
    mean_value: 128
    mirror: true
  }
  video_data_param {
    source: "train_02.lst"
    root_folder: "/home/liupai/hme-workspace/train-data/UCF101/"
    new_length: 8
    sampling_rate: 2
    new_height: 128
    new_width: 171
    use_image: false
    show_data: false
    batch_size: 30
    shuffle: true
  }
}