Python Permission Denied with ffprobe on NamedTemporaryFile

Question

I'm trying to validate certain parameters of a media file before the file gets saved in Django. So I validate the file using ffprobe (from the ffmpeg pip package).

with NamedTemporaryFile(suffix=f'.{self.audio.name.split(".")[-1]}') as fp:
    fp.write(self.audio.read())
    try:
        # Get duration with ffprobe
        info = probe(fp.name)
        self.duration = info['format']['duration']
        fp.close()
    except ffmpeg.Error as e:
        print('stderr:', e.stderr.decode('utf8'))
        raise NotAudioFile
    except:
        traceback.print_exc()
        raise NotAudioFile

This is the snippet that validates the file. self.audio is a Django FileField. It creates a named temporary file, writes the file from the django file, and then validates it using ffprobe.

However, when it runs, ffprobe gives me a Permission Denied error, which is weird, since I checked the file and I have full permission to write that directory/file.

stderr: ffprobe version 4.3.2-2021-02-20-essentials_build-www.gyan.dev Copyright (c) 2007-2021 the FFmpeg developers
  built with gcc 10.2.0 (Rev6, Built by MSYS2 project)
  configuration: --enable-gpl --enable-version3 --enable-static --disable-w32threads --disable-autodetect --enable-fontconfig --enable-iconv --enable-gnutls --enable-libxml2 --enable-gmp --enable-lzma --enable-zlib --enable-libsr
t --enable-libssh --enable-libzmq --enable-avisynth --enable-sdl2 --enable-libwebp --enable-libx264 --enable-libx265 --enable-libxvid --enable-libaom --enable-libopenjpeg --enable-libvpx --enable-libass --enable-libfreetype --ena
ble-libfribidi --enable-libvidstab --enable-libvmaf --enable-libzimg --enable-amf --enable-cuda-llvm --enable-cuvid --enable-ffnvcodec --enable-nvdec --enable-nvenc --enable-d3d11va --enable-dxva2 --enable-libmfx --enable-libgme
--enable-libopenmpt --enable-libopencore-amrwb --enable-libmp3lame --enable-libtheora --enable-libvo-amrwbenc --enable-libgsm --enable-libopencore-amrnb --enable-libopus --enable-libspeex --enable-libvorbis --enable-librubberband
  libavutil      56. 51.100 / 56. 51.100
  libavcodec     58. 91.100 / 58. 91.100
  libavformat    58. 45.100 / 58. 45.100
  libavdevice    58. 10.100 / 58. 10.100
  libavfilter     7. 85.100 /  7. 85.100
  libswscale      5.  7.100 /  5.  7.100
  libswresample   3.  7.100 /  3.  7.100
  libpostproc    55.  7.100 / 55.  7.100
C:\Users\cclloyd\AppData\Local\Temp\tmp9lhjsl9n.mp3: Permission denied

So why is it giving me that error?

Answer 1

As per the documentation :

...name can be retrieved from the name attribute of the returned file-like object. Whether the name can be used to open the file a second time, while the named temporary file is still open, varies across platforms (it can be so used on Unix; it cannot on Windows NT or later ). If delete is true ( the default ), the file is deleted as soon as it is closed.

When you pass fp.name to probe() function, the ffprobe process attempts to access/open the file, but - as described above and here - Windows does not allow processes other than the one used to create the NamedTemporaryFile to access the file when the delete is set to True . Thus, you should set delete to False when creating a new instance of a NamedTemporaryFile , and delete the file once you are done with it using the os.remove() or os.unlink() method. Example below:

f = NamedTemporaryFile(delete=False, suffix=f'.{self.audio.name.split(".")[-1]}')
try:
    f.write(self.audio.read())
    try:
        # Get duration with ffprobe
        info = probe(f.name)
        self.duration = info['format']['duration']
    except ffmpeg.Error as e:
        print('stderr:', e.stderr.decode('utf8'))
        raise NotAudioFile
    except:
        traceback.print_exc()
        raise NotAudioFile
finally:
    f.close()
    os.unlink(f.name)  # delete the file

Answer 2

FWIW, I posted a helper class that wraps the solution proposed by @Chris here: https://stackoverflow.com/a/73344950/19166