How do I read back errors?

When I get this back from ffmpeg ffprobe error (see stderr output for detail) I do not know how to check the stderr output for the details.

import sys

import ffmpeg
from ffmpeg import Error as FFmpegError

try:
    duration = ffmpeg.probe('https://www.youtube.com/watch?v=cv4123_39ddfa324LB23MsYg')['format']['duration']
    
except FFmpegError as e:
    print(e)

    # doesn't work
    # for line in sys.stderr:
        # print(line)

    # doesn't work
    # data = sys.stderr.readlines()
    # print(data)

Couldn’t find an example of this in the documentation and couldn’t figure it out myself.

[evictor]

With some finagling I came up with this:

1. Pass args capture_stdout=True, capture_stderr=True to run()
2. Theoretically the run() func returns tuple (out, err) so you can receive those; however…
3. If the return code is nonzero the function throws so you should probably catch that and print:

            try:
                ffmpeg.input(...) \
                    .output(...) \
                    .run(capture_stdout=True, capture_stderr=True)
            except ffmpeg.Error as e:
                print('stdout:', e.stdout.decode('utf8'))
                print('stderr:', e.stderr.decode('utf8'))
                raise e

[CodeStrumpet]

Just ran into this as well (could not figure out how to read stderr coming from probe). Finally (after a lot of unsuccessful googling) I found the answer in a nicely placed comment in the the source code:

From ffmpeg-python/ffmpeg/_probe.py:

    Raises:
        :class:`ffmpeg.Error`: if ffprobe returns a non-zero exit code,
            an :class:`Error` is returned with a generic error message.
            The stderr output can be retrieved by accessing the
            ``stderr`` property of the exception.

So this is what worked for me:

try:
    probe = ffmpeg.probe(video_path)
    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'])
    duration = float(video_stream['duration'])
except ffmpeg.Error as e:
    print(e.stderr)