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decord_reader.py
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decord_reader.py
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#
# For licensing see accompanying LICENSE file.
# Copyright (C) 2024 Apple Inc. All Rights Reserved.
#
import sys
from typing import Dict, Optional, Union
from corenet.data.transforms.base_transforms import BaseTransformation
from corenet.utils.import_utils import ensure_library_is_available
try:
import decord
except ImportError:
pass
import av
import torch
from corenet.data.video_reader import VIDEO_READER_REGISTRY
from corenet.data.video_reader.pyav_reader import BaseAVReader
from corenet.utils import logger
@VIDEO_READER_REGISTRY.register(name="decord")
class DecordAVReader(BaseAVReader):
"""
Video Reader using Decord.
"""
def __init__(self, *args, **kwargs):
ensure_library_is_available("decord")
super().__init__(*args, **kwargs)
def read_video(
self,
av_file: str,
stream_idx: int = 0,
audio_sample_rate: int = -1,
custom_frame_transforms: Optional[BaseTransformation] = None,
video_only: bool = False,
*args,
**kwargs
) -> Dict:
video_frames = audio_frames = None
video_fps = audio_fps = None
decord.bridge.set_bridge("torch")
# We have to use av package to obtain audio fps, which is not available in
# decord.
with av.open(str(av_file)) as container:
available_streams = []
for stream in container.streams:
if stream.type == "audio":
# Skip audio stream if audio not required.
if video_only:
continue
audio_fps = container.streams.audio[0].sample_rate
available_streams.append(stream.type)
for stream_type in available_streams:
if stream_type == "video":
with open(str(av_file), "rb") as f:
video_reader = decord.VideoReader(f, ctx=decord.cpu(0))
n_video_frames = video_reader._num_frame
video_frames = []
frame_transforms = (
self.frame_transforms
if custom_frame_transforms is None
else custom_frame_transforms
)
for _ in range(n_video_frames):
video_frame = video_reader.next() # H, W, C
video_frame = video_frame.permute(2, 0, 1) # C, H, W
video_frame = frame_transforms({"image": video_frame})["image"]
video_frames.append(video_frame)
video_frames = torch.stack(video_frames)
video_fps = video_reader.get_avg_fps()
if stream_type == "audio":
with open(str(av_file), "rb") as f:
audio_reader = decord.AudioReader(
f, ctx=decord.cpu(0), sample_rate=audio_sample_rate
)
audio_frames = torch.tensor(audio_reader._array).transpose(0, 1)
audio_fps = (
audio_sample_rate if audio_sample_rate > 0 else audio_fps
)
return {
"audio": audio_frames, # expected format T x C
"video": video_frames, # expected format T x C x H x W
"metadata": {
"audio_fps": audio_fps,
"video_fps": video_fps,
"filename": av_file,
},
}
def build_video_metadata(
self, video_path: str
) -> Dict[str, Union[str, float, int]]:
"""Generate the metadata for a given video.
Args:
video_path: A video file path.
Returns:
The metadata of the corresponding video. The generated metadata format is:
{
"filename": <str>,
"video_fps": <float>,
"total_video_frames" <int>,
"video_duration": <float>,
}
"""
vmetadata = {}
vr = decord.VideoReader(video_path, ctx=decord.cpu(0), num_threads=1)
with av.open(video_path) as container:
vmetadata["filename"] = video_path
video_stream = container.streams.video[0]
vmetadata["total_video_frames"] = len(vr)
vmetadata["video_fps"] = float(vr.get_avg_fps())
vmetadata["video_duration"] = (
vmetadata["total_video_frames"] / vmetadata["video_fps"]
)
return vmetadata
def build_audio_metadata(
self, video_path: str
) -> Dict[str, Union[str, float, int]]:
"""Generate the audio metadata for a given video.
Args:
video_path: A video file path.
Returns:
The audio metadata of the corresponding video. The metadata format is:
{
"audio_channels": int,
"audio_fps": int,
"total_audio_frames": int,
"audio_duration": float,
}
"""
metadata = {}
# Decord doesn't provide audio_fps. Thus, we use PyAV.
with av.open(str(video_path)) as container:
for stream in container.streams:
container.seek(0)
if stream.type == "audio":
if "audio_fps" in metadata:
raise ValueError(
"Multiple audio streams exist while at most 1 is expected."
)
audio_stream = container.streams.audio[0]
metadata["audio_channels"] = len(audio_stream.layout.channels)
metadata["audio_fps"] = audio_stream.sample_rate
# `audio_stream.frames` does not work for unknown reason.
metadata["total_audio_frames"] = self._get_total_audio_frames(
video_path, audio_stream.sample_rate
)
metadata["audio_duration"] = (
metadata["total_audio_frames"] / metadata["audio_fps"]
)
return metadata
@staticmethod
def _get_total_audio_frames(video_path: str, sample_rate: Union[int, float]) -> int:
"""Returns the total number frames in the audio stream of @video_path.
Args:
video_path: Path to the local video file.
sample_rate: Sample rate of the audio stream.
"""
with open(str(video_path), "rb") as f:
# FIXME: Type of the @sample_rate is Union[int,float], but decord expects an
# integer. We should investigate what happens when floating point values are
# passed to this function. This issue might cause some misalignment between
# the audio and the video.
audio_reader = decord.AudioReader(
f, ctx=decord.cpu(0), sample_rate=sample_rate
)
result = audio_reader.shape[1]
return result