"RuntimeError: Not compiled with video_reader support" raises when I use the new fine-grained VideoReader API

[caddyless]

🐛 Bug

I wanna compare the performance of the new fine-grained video read API in pytorch 1.7 to that in opencv, thus I do a experiment.
When I wanna to read a MP4 format video with the new VideoReader API in the torchvision.io.video, a "RuntimeError: Not compiled with video_reader support" raised. Referring to the source code, I found it's caused by the _HAS_VIDEO_OPT variable is False. More precisely, it is caused by the source code in file vision/torchvision/io/_video_opt.py line 15-24 (as follow). The function "extfilder.find_spec('video_reader')" return None lead to that Error. I wanna know why and how to avoid it. Thanks lots!

By the way, the old video read API read_video() works well.

To Reproduce

Steps to reproduce the behavior:

1.call the class VideoReader and pass in file path of a video in MP4 format.

The source code:

The error message:

Expected behavior

The class return a video reading handler object without any error.

Environment

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python collect_env.py

• PyTorch Version (e.g., 1.0): 1.7
• OS (e.g., Linux): Ubuntu 16.04
• How you installed PyTorch (conda, pip, source): conda
• Build command you used (if compiling from source):
• Python version: 3.8
• CUDA/cuDNN version: 11.0
• GPU models and configuration: 2080Ti
• Any other relevant information:

Additional context

cc @bjuncek

[vfdev-5]

@caddyless VideoReader API is still in beta and we suggest :

In order to use the Video Reader API, you need to compile torchvision from source and make sure that you have ffmpeg installed in your system.

Please, see the release note : https://github.com/pytorch/vision/releases/tag/v0.8.0

[fmassa]

Hi,

The current behavior is expected, and you need to compile torchvision from source in order to have the new VideoReader API.

In future releases of torchvision we will have it be package by default with the torchvision binaries so that using it will be easier.

As this is the expected behavior for now, I'm closing this issue but let us know if you have further questions

[Queuecumber]

Is the API still in beta? I dont see it marked as such on the documentation but I still get this error on torchvision 0.10.0

[fmassa]

@Queuecumber yes, we still have some things we need to fix before we can make it to stable

[nicobrb]

Is there a tutorial on how to compile from source? I'm using Windows, I can't find anything online.

[rathodparmeshwar]

Even building it with source produce same error.