Reading/Writing images and videos¶
The torchvision.io
package provides functions for performing IO
operations. They are currently specific to reading and writing video and
images.
Video¶
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Reads a video from a file, returning both the video frames as well as the audio frames |
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List the video frames timestamps. |
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Writes a 4d tensor in [T, H, W, C] format in a video file |
Fine-grained video API¶
In addition to the read_video
function, we provide a high-performance
lower-level API for more fine-grained control compared to the read_video
function.
It does all this whilst fully supporting torchscript.
Warning
The fine-grained video API is in Beta stage, and backward compatibility is not guaranteed.
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Fine-grained video-reading API. |
Example of inspecting a video:
import torchvision
video_path = "path to a test video"
# Constructor allocates memory and a threaded decoder
# instance per video. At the moment it takes two arguments:
# path to the video file, and a wanted stream.
reader = torchvision.io.VideoReader(video_path, "video")
# The information about the video can be retrieved using the
# `get_metadata()` method. It returns a dictionary for every stream, with
# duration and other relevant metadata (often frame rate)
reader_md = reader.get_metadata()
# metadata is structured as a dict of dicts with following structure
# {"stream_type": {"attribute": [attribute per stream]}}
#
# following would print out the list of frame rates for every present video stream
print(reader_md["video"]["fps"])
# we explicitly select the stream we would like to operate on. In
# the constructor we select a default video stream, but
# in practice, we can set whichever stream we would like
video.set_current_stream("video:0")
Image¶
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Support for various modes while reading images. |
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Reads a JPEG or PNG image into a 3 dimensional RGB or grayscale Tensor. |
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Detects whether an image is a JPEG or PNG and performs the appropriate operation to decode the image into a 3 dimensional RGB or grayscale Tensor. |
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Takes an input tensor in CHW layout and returns a buffer with the contents of its corresponding JPEG file. |
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Decodes a JPEG image into a 3 dimensional RGB or grayscale Tensor. |
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Takes an input tensor in CHW layout and saves it in a JPEG file. |
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Takes an input tensor in CHW layout and returns a buffer with the contents of its corresponding PNG file. |
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Decodes a PNG image into a 3 dimensional RGB or grayscale Tensor. |
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Takes an input tensor in CHW layout (or HW in the case of grayscale images) and saves it in a PNG file. |
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Reads and outputs the bytes contents of a file as a uint8 Tensor with one dimension. |
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Writes the contents of a uint8 tensor with one dimension to a file. |