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• NumPy array of a video changes from the original after writing into the same video

  29 mars 2021, par Rashiq

  I have a video (test.mkv) that I have converted into a 4D NumPy array - (frame, height, width, color_channel). I have even managed to convert that array back into the same video (test_2.mkv) without altering anything. However, after reading this new, test_2.mkv, back into a new NumPy array, the array of the first video is different from the second video's array i.e. their hashes don't match and the numpy.array_equal() function returns false. I have tried using both python-ffmpeg and scikit-video but cannot get the arrays to match.

  


  Python-ffmpeg attempt :

  


  import ffmpeg
import numpy as np
import hashlib

file_name = 'test.mkv'

# Get video dimensions and framerate
probe = ffmpeg.probe(file_name)
video_stream = next((stream for stream in probe['streams'] if stream['codec_type'] == 'video'), None)
width = int(video_stream['width'])
height = int(video_stream['height'])
frame_rate = video_stream['avg_frame_rate']

# Read video into buffer
out, error = (
    ffmpeg
        .input(file_name, threads=120)
        .output("pipe:", format='rawvideo', pix_fmt='rgb24')
        .run(capture_stdout=True)
)

# Convert video buffer to array
video = (
    np
        .frombuffer(out, np.uint8)
        .reshape([-1, height, width, 3])
)

# Convert array to buffer
video_buffer = (
    np.ndarray
        .flatten(video)
        .tobytes()
)

# Write buffer back into a video
process = (
    ffmpeg
        .input('pipe:', format='rawvideo', s='{}x{}'.format(width, height))
        .output("test_2.mkv", r=frame_rate)
        .overwrite_output()
        .run_async(pipe_stdin=True)
)
process.communicate(input=video_buffer)

# Read the newly written video
out_2, error = (
    ffmpeg
        .input("test_2.mkv", threads=40)
        .output("pipe:", format='rawvideo', pix_fmt='rgb24')
        .run(capture_stdout=True)
)

# Convert new video into array
video_2 = (
    np
        .frombuffer(out_2, np.uint8)
        .reshape([-1, height, width, 3])
)

# Video dimesions change
print(f'{video.shape} vs {video_2.shape}') # (844, 1080, 608, 3) vs (2025, 1080, 608, 3)
print(f'{np.array_equal(video, video_2)}') # False

# Hashes don't match
print(hashlib.sha256(bytes(video_2)).digest()) # b'\x88\x00\xc8\x0ed\x84!\x01\x9e\x08 \xd0U\x9a(\x02\x0b-\xeeA\xecU\xf7\xad0xa\x9e\\\xbck\xc3'
print(hashlib.sha256(bytes(video)).digest()) # b'\x9d\xc1\x07xh\x1b\x04I\xed\x906\xe57\xba\xf3\xf1k\x08\xfa\xf1\xfaM\x9a\xcf\xa9\t8\xf0\xc9\t\xa9\xb7'


  


  Scikit-video attempt :

  


  import skvideo.io as sk
import numpy as np

video_data = sk.vread('test.mkv')

sk.vwrite('test_2_ski.mkv', video_data)

video_data_2 = sk.vread('test_2_ski.mkv')

# Dimensions match but...
print(video_data.shape) # (844, 1080, 608, 3)
print(video_data_2.shape) # (844, 1080, 608, 3)

# ...array elements don't
print(np.array_equal(video_data, video_data_2)) # False

# Hashes don't match either
print(hashlib.sha256(bytes(video_2)).digest()) # b'\x8b?]\x8epD:\xd9B\x14\xc7\xba\xect\x15G\xfaRP\xde\xad&EC\x15\xc3\x07\n{a[\x80'
print(hashlib.sha256(bytes(video)).digest()) # b'\x9d\xc1\x07xh\x1b\x04I\xed\x906\xe57\xba\xf3\xf1k\x08\xfa\xf1\xfaM\x9a\xcf\xa9\t8\xf0\xc9\t\xa9\xb7'


  


  I don't understand where I'm going wrong and both the respective documentations do not highlight how to do this particular task. Any help is appreciated. Thank you.

  


• How to quote a file name with a single quote in ffmpeg movie= filter notation ? [closed]

  26 mai, par PieterV

  I am trying to run ffmpeg using a file that contains a single quote ' in the filename.

  


  I tried to follow the docs that say I should replace a ' with '\''.
  
And a ticket that says I should replace a ' with \\\\\'.

  


  I've tried both, and can't get get it working.

  


  E.g. docs format :

  


  ./ffprobe -loglevel error -read_intervals %00:30 -select_streams s:0 -f lavfi -i "movie='D\:\\Test\\Interlaced - Dragons'\'' Den - S14E02 - Episode 2.mkv'[out0+subcc]" -show_packets -print_format json

{
[Parsed_movie_0 @ 00000222a2f82200] Failed to avformat_open_input 'D:\Test\Interlaced - Dragons Den - S14E02 - Episode 2.mkv'
[AVFilterGraph @ 00000222a2f76ec0] Error processing filtergraph: No such file or directory
movie='D\:\\Test\\Interlaced - Dragons'\'' Den - S14E02 - Episode 2.mkv'[out0+subcc]: No such file or directory


  


  E.g. ticket format :

  


  ./ffprobe -loglevel error -read_intervals %00:30 -select_streams s:0 -f lavfi -i "movie='D\:\\Test\\Interlaced - Dragons\\\\\' Den - S14E02 - Episode 2.mkv'[out0+subcc]" -show_packets -print_format json

{
[Parsed_movie_0 @ 00000158613d2080] Failed to avformat_open_input 'D:\Test\Interlaced - Dragons\\ Den - S14E02 - Episode 2.mkv[out0+subcc]'
[AVFilterGraph @ 00000158613c6ec0] Error processing filtergraph: No such file or directory
movie='D\:\\Test\\Interlaced - Dragons\\\\\' Den - S14E02 - Episode 2.mkv'[out0+subcc]: No such file or directory


  


  > dir "D:\Test\Interlaced - Dragons' Den - S14E02 - Episode 2.mkv"

    Directory: D:\Test

Mode                 LastWriteTime         Length Name
----                 -------------         ------ ----
-a---           4/20/2025 11:38 AM       18059051 Interlaced - Dragons' Den - S14E02 - Episode 2.mkv


  


  This is on Win11 using FFmpeg7.
  
Any ideas ?

  


  [Update]
  
I found a doc on escape filtergraph strings, did not help, I tried 0 to 7 \.

  


  I also found and tried the ffescape utility, the output it produces just uses a single \' and does not work.

  


  > echo "D:\Test\Interlaced - Dragons' Den - S14E02 - Episode 2.mkv" | ./ffescape.exe
=> D:\\Test\\Interlaced - Dragons\' Den - S14E02 - Episode 2.mkv\

> ./ffprobe -loglevel error -read_intervals %00:30 -select_streams s:0 -f lavfi -i "movie='D:\\Test\\Interlaced - Dragons\' Den - S14E02 - Episode 2.mkv\'[out0+subcc]" -show_packets -print_format json
{
[Parsed_movie_0 @ 0000021348f12200] Failed to avformat_open_input 'D'
[AVFilterGraph @ 0000021348f06ec0] Error processing filtergraph: No such file or directory
movie='D:\\Test\\Interlaced - Dragons\' Den - S14E02 - Episode 2.mkv\'[out0+subcc]: No such file or directory


  


  [Update]
  
I found docs for ffmpeg filter script where I can place commands in a file.

  


  I tried ./ffprobe -loglevel error -read_intervals %00:01 -select_streams s:0 -f lavfi -/i "d:\filtergraph.txt" -show_packets -print_format json, and it load the script.

  


  Works : movie=test.mkv[out0+subcc]\ if test.mkv is in ffprobe dir.
Works : movie=test\'.mkv[out0+subcc]\ if test'.mkv is in ffprobe dir.
  
Not : movie=D:\test.mkv[out0+subcc]
  
Not : movie=D\:\\test.mkv[out0+subcc]
  
Not : movie=test space.mkv[out0+subcc]
  
Not : movie='test space.mkv[out0+subcc]'
  
Not : movie="test space.mkv[out0+subcc]"
  
Not : 'movie=test space.mkv[out0+subcc]'
  
Not : "movie=test space.mkv[out0+subcc]"

  


   :(

  


  Update with working answer

  


• v4l2loopback+ffmpeg input for uvc gadget

  13 mai, par Mosi

  I'm trying to use an MP4 video file as the input for a UVC Gadget setup on my Raspberry Pi 4 Model B, but I'm running into an issue when streaming through V4L2.

  


  Goal :

  


  To emulate a webcam that streams a looping MP4 video file to a Windows 11 host.

  


  My setup :

  


  

  • Hardware : Raspberry Pi 4 Model B

  


  • OS : Raspberry Pi OS Lite 64-bit (2025-05-06-raspios-bookworm-arm64-lite)

  


  • Kernel : 6.12.25+rpt-rpi-v8

  


  • Host System : Windows 11

  


  • UVC Gadget version : v0.3.0

  


  


  Workflow :

  


  [MP4 Video] → [FFmpeg] → [V4L2 Loopback] → [UVC Gadget] → Windows sees virtual webcam


  


  What works :

  


  The UVC Gadget works perfectly when I use a real webcam as the source (e.g., /dev/video0). Windows detects the virtual webcam and displays a smooth video stream.

  


  The problem :

  


  When I try to use an MP4 video file through FFmpeg and send it to the loopback device (/dev/video3), the UVC Gadget fails with the following error :

  


  ---

  


  Command I'm using :

  


  ffmpeg -re -stream_loop -1 -i input.mp4 -vf scale=640:480 \
  -c:v rawvideo -pix_fmt yuyv422 -r 30 -f v4l2 /dev/video3


  


  Then I run :

  


  sudo uvc-gadget -d /dev/video3 uvc.0


  


  Output :

  


  bRequestType 21 bRequest 01 wValue 0200 wIndex 0001 wLength 0022
streaming request (req SET_CUR cs 02)
setting commit control, length = 34
Setting format to 0x56595559 640x480
=== Setting frame rate to 30 fps
Starting video stream.
--> [At this point I open the camera on the Windows host]
/dev/video3: 2 buffers requested.
Failed to export buffer 0.
Failed to export buffers on source: Inappropriate ioctl for device (25)


  


  ---

  


  Things I've tried :

  


  

  • Multiple FFmpeg formats, resolutions, and pixel formats

  


  • Various ffmpeg buffer and framerate tweaks

  


  • Different UVC Gadget versions

  


  • GitHub related projects (showcamera, etc.)

  


  • Older Raspberry Pi OS versions

  


  


  Most guides and GitHub projects I found are outdated (5+ years old), and newer methods seem undocumented or incompatible with current kernel/UVC gadget tools.

  


  ---

  


  My question :

  


  How can I stream an MP4 file as a virtual webcam using UVC Gadget without getting ioctl errors ?
  
Is there a proper way to set up FFmpeg and loopback devices so that UVC Gadget can read the stream correctly ?

  


  Any modern working example or tips would be very appreciated. Thanks in advance !