import bisect import math import warnings from fractions import Fraction from typing import List import torch from torchvision.io import ( _probe_video_from_file, _read_video_from_file, read_video, read_video_timestamps, ) from .utils import tqdm def pts_convert(pts, timebase_from, timebase_to, round_func=math.floor): """convert pts between different time bases Args: pts: presentation timestamp, float timebase_from: original timebase. Fraction timebase_to: new timebase. Fraction round_func: rounding function. """ new_pts = Fraction(pts, 1) * timebase_from / timebase_to return round_func(new_pts) def unfold(tensor, size, step, dilation=1): """ similar to tensor.unfold, but with the dilation and specialized for 1d tensors Returns all consecutive windows of `size` elements, with `step` between windows. The distance between each element in a window is given by `dilation`. """ assert tensor.dim() == 1 o_stride = tensor.stride(0) numel = tensor.numel() new_stride = (step * o_stride, dilation * o_stride) new_size = ((numel - (dilation * (size - 1) + 1)) // step + 1, size) if new_size[0] < 1: new_size = (0, size) return torch.as_strided(tensor, new_size, new_stride) class _VideoTimestampsDataset: """ Dataset used to parallelize the reading of the timestamps of a list of videos, given their paths in the filesystem. Used in VideoClips and defined at top level so it can be pickled when forking. """ def __init__(self, video_paths: List[str]): self.video_paths = video_paths def __len__(self): return len(self.video_paths) def __getitem__(self, idx): return read_video_timestamps(self.video_paths[idx]) def _collate_fn(x): """ Dummy collate function to be used with _VideoTimestampsDataset """ return x class VideoClips: """ Given a list of video files, computes all consecutive subvideos of size `clip_length_in_frames`, where the distance between each subvideo in the same video is defined by `frames_between_clips`. If `frame_rate` is specified, it will also resample all the videos to have the same frame rate, and the clips will refer to this frame rate. Creating this instance the first time is time-consuming, as it needs to decode all the videos in `video_paths`. It is recommended that you cache the results after instantiation of the class. Recreating the clips for different clip lengths is fast, and can be done with the `compute_clips` method. Args: video_paths (List[str]): paths to the video files clip_length_in_frames (int): size of a clip in number of frames frames_between_clips (int): step (in frames) between each clip frame_rate (int, optional): if specified, it will resample the video so that it has `frame_rate`, and then the clips will be defined on the resampled video num_workers (int): how many subprocesses to use for data loading. 0 means that the data will be loaded in the main process. (default: 0) """ def __init__( self, video_paths, clip_length_in_frames=16, frames_between_clips=1, frame_rate=None, _precomputed_metadata=None, num_workers=0, _video_width=0, _video_height=0, _video_min_dimension=0, _video_max_dimension=0, _audio_samples=0, _audio_channels=0, ): self.video_paths = video_paths self.num_workers = num_workers # these options are not valid for pyav backend self._video_width = _video_width self._video_height = _video_height self._video_min_dimension = _video_min_dimension self._video_max_dimension = _video_max_dimension self._audio_samples = _audio_samples self._audio_channels = _audio_channels if _precomputed_metadata is None: self._compute_frame_pts() else: self._init_from_metadata(_precomputed_metadata) self.compute_clips(clip_length_in_frames, frames_between_clips, frame_rate) def _compute_frame_pts(self): self.video_pts = [] self.video_fps = [] # strategy: use a DataLoader to parallelize read_video_timestamps # so need to create a dummy dataset first import torch.utils.data dl = torch.utils.data.DataLoader( _VideoTimestampsDataset(self.video_paths), batch_size=16, num_workers=self.num_workers, collate_fn=_collate_fn, ) with tqdm(total=len(dl)) as pbar: for batch in dl: pbar.update(1) clips, fps = list(zip(*batch)) # we need to specify dtype=torch.long because for empty list, # torch.as_tensor will use torch.float as default dtype. This # happens when decoding fails and no pts is returned in the list. clips = [torch.as_tensor(c, dtype=torch.long) for c in clips] self.video_pts.extend(clips) self.video_fps.extend(fps) def _init_from_metadata(self, metadata): self.video_paths = metadata["video_paths"] assert len(self.video_paths) == len(metadata["video_pts"]) self.video_pts = metadata["video_pts"] assert len(self.video_paths) == len(metadata["video_fps"]) self.video_fps = metadata["video_fps"] @property def metadata(self): _metadata = { "video_paths": self.video_paths, "video_pts": self.video_pts, "video_fps": self.video_fps, } return _metadata def subset(self, indices): video_paths = [self.video_paths[i] for i in indices] video_pts = [self.video_pts[i] for i in indices] video_fps = [self.video_fps[i] for i in indices] metadata = { "video_paths": video_paths, "video_pts": video_pts, "video_fps": video_fps, } return type(self)( video_paths, self.num_frames, self.step, self.frame_rate, _precomputed_metadata=metadata, num_workers=self.num_workers, _video_width=self._video_width, _video_height=self._video_height, _video_min_dimension=self._video_min_dimension, _video_max_dimension=self._video_max_dimension, _audio_samples=self._audio_samples, _audio_channels=self._audio_channels, ) @staticmethod def compute_clips_for_video(video_pts, num_frames, step, fps, frame_rate): if fps is None: # if for some reason the video doesn't have fps (because doesn't have a video stream) # set the fps to 1. The value doesn't matter, because video_pts is empty anyway fps = 1 if frame_rate is None: frame_rate = fps total_frames = len(video_pts) * (float(frame_rate) / fps) idxs = VideoClips._resample_video_idx(int(math.floor(total_frames)), fps, frame_rate) video_pts = video_pts[idxs] clips = unfold(video_pts, num_frames, step) if not clips.numel(): warnings.warn( "There aren't enough frames in the current video to get a clip for the given clip length and " "frames between clips. The video (and potentially others) will be skipped." ) if isinstance(idxs, slice): idxs = [idxs] * len(clips) else: idxs = unfold(idxs, num_frames, step) return clips, idxs def compute_clips(self, num_frames, step, frame_rate=None): """ Compute all consecutive sequences of clips from video_pts. Always returns clips of size `num_frames`, meaning that the last few frames in a video can potentially be dropped. Args: num_frames (int): number of frames for the clip step (int): distance between two clips frame_rate (int, optional): The frame rate """ self.num_frames = num_frames self.step = step self.frame_rate = frame_rate self.clips = [] self.resampling_idxs = [] for video_pts, fps in zip(self.video_pts, self.video_fps): clips, idxs = self.compute_clips_for_video(video_pts, num_frames, step, fps, frame_rate) self.clips.append(clips) self.resampling_idxs.append(idxs) clip_lengths = torch.as_tensor([len(v) for v in self.clips]) self.cumulative_sizes = clip_lengths.cumsum(0).tolist() def __len__(self): return self.num_clips() def num_videos(self): return len(self.video_paths) def num_clips(self): """ Number of subclips that are available in the video list. """ return self.cumulative_sizes[-1] def get_clip_location(self, idx): """ Converts a flattened representation of the indices into a video_idx, clip_idx representation. """ video_idx = bisect.bisect_right(self.cumulative_sizes, idx) if video_idx == 0: clip_idx = idx else: clip_idx = idx - self.cumulative_sizes[video_idx - 1] return video_idx, clip_idx @staticmethod def _resample_video_idx(num_frames, original_fps, new_fps): step = float(original_fps) / new_fps if step.is_integer(): # optimization: if step is integer, don't need to perform # advanced indexing step = int(step) return slice(None, None, step) idxs = torch.arange(num_frames, dtype=torch.float32) * step idxs = idxs.floor().to(torch.int64) return idxs def get_clip(self, idx): """ Gets a subclip from a list of videos. Args: idx (int): index of the subclip. Must be between 0 and num_clips(). Returns: video (Tensor) audio (Tensor) info (Dict) video_idx (int): index of the video in `video_paths` """ if idx >= self.num_clips(): raise IndexError(f"Index {idx} out of range ({self.num_clips()} number of clips)") video_idx, clip_idx = self.get_clip_location(idx) video_path = self.video_paths[video_idx] clip_pts = self.clips[video_idx][clip_idx] from torchvision import get_video_backend backend = get_video_backend() if backend == "pyav": # check for invalid options if self._video_width != 0: raise ValueError("pyav backend doesn't support _video_width != 0") if self._video_height != 0: raise ValueError("pyav backend doesn't support _video_height != 0") if self._video_min_dimension != 0: raise ValueError("pyav backend doesn't support _video_min_dimension != 0") if self._video_max_dimension != 0: raise ValueError("pyav backend doesn't support _video_max_dimension != 0") if self._audio_samples != 0: raise ValueError("pyav backend doesn't support _audio_samples != 0") if backend == "pyav": start_pts = clip_pts[0].item() end_pts = clip_pts[-1].item() video, audio, info = read_video(video_path, start_pts, end_pts) else: info = _probe_video_from_file(video_path) video_fps = info.video_fps audio_fps = None video_start_pts = clip_pts[0].item() video_end_pts = clip_pts[-1].item() audio_start_pts, audio_end_pts = 0, -1 audio_timebase = Fraction(0, 1) video_timebase = Fraction(info.video_timebase.numerator, info.video_timebase.denominator) if info.has_audio: audio_timebase = Fraction(info.audio_timebase.numerator, info.audio_timebase.denominator) audio_start_pts = pts_convert(video_start_pts, video_timebase, audio_timebase, math.floor) audio_end_pts = pts_convert(video_end_pts, video_timebase, audio_timebase, math.ceil) audio_fps = info.audio_sample_rate video, audio, info = _read_video_from_file( video_path, video_width=self._video_width, video_height=self._video_height, video_min_dimension=self._video_min_dimension, video_max_dimension=self._video_max_dimension, video_pts_range=(video_start_pts, video_end_pts), video_timebase=video_timebase, audio_samples=self._audio_samples, audio_channels=self._audio_channels, audio_pts_range=(audio_start_pts, audio_end_pts), audio_timebase=audio_timebase, ) info = {"video_fps": video_fps} if audio_fps is not None: info["audio_fps"] = audio_fps if self.frame_rate is not None: resampling_idx = self.resampling_idxs[video_idx][clip_idx] if isinstance(resampling_idx, torch.Tensor): resampling_idx = resampling_idx - resampling_idx[0] video = video[resampling_idx] info["video_fps"] = self.frame_rate assert len(video) == self.num_frames, f"{video.shape} x {self.num_frames}" return video, audio, info, video_idx def __getstate__(self): video_pts_sizes = [len(v) for v in self.video_pts] # To be back-compatible, we convert data to dtype torch.long as needed # because for empty list, in legacy implementation, torch.as_tensor will # use torch.float as default dtype. This happens when decoding fails and # no pts is returned in the list. video_pts = [x.to(torch.int64) for x in self.video_pts] # video_pts can be an empty list if no frames have been decoded if video_pts: video_pts = torch.cat(video_pts) # avoid bug in https://github.com/pytorch/pytorch/issues/32351 # TODO: Revert it once the bug is fixed. video_pts = video_pts.numpy() # make a copy of the fields of self d = self.__dict__.copy() d["video_pts_sizes"] = video_pts_sizes d["video_pts"] = video_pts # delete the following attributes to reduce the size of dictionary. They # will be re-computed in "__setstate__()" del d["clips"] del d["resampling_idxs"] del d["cumulative_sizes"] # for backwards-compatibility d["_version"] = 2 return d def __setstate__(self, d): # for backwards-compatibility if "_version" not in d: self.__dict__ = d return video_pts = torch.as_tensor(d["video_pts"], dtype=torch.int64) video_pts = torch.split(video_pts, d["video_pts_sizes"], dim=0) # don't need this info anymore del d["video_pts_sizes"] d["video_pts"] = video_pts self.__dict__ = d # recompute attributes "clips", "resampling_idxs" and other derivative ones self.compute_clips(self.num_frames, self.step, self.frame_rate)