set up error about "av"

I have followed the instruction of the INSTALL.md, and have installed all required library.
But when I built pyslowfast, I met this error as follow:

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(PySlowFast) cjj@cjj-hp:~/PycharmProjects/PySlowFast/slowfast$ python setup.py build develop
running build
running build_py
running develop
running egg_info
writing slowfast.egg-info/PKG-INFO
writing dependency_links to slowfast.egg-info/dependency_links.txt
writing requirements to slowfast.egg-info/requires.txt
writing top-level names to slowfast.egg-info/top_level.txt
reading manifest file 'slowfast.egg-info/SOURCES.txt'
writing manifest file 'slowfast.egg-info/SOURCES.txt'
running build_ext
Creating /home/cjj/anaconda3/lib/python3.7/site-packages/slowfast.egg-link (link to .)
Adding slowfast 1.0 to easy-install.pth file

Installed /home/cjj/PycharmProjects/PySlowFast/slowfast
Processing dependencies for slowfast==1.0
Searching for av
Reading https://pypi.org/simple/av/
Downloading https://files.pythonhosted.org/packages/8e/7a/be91247d5d1613ce3a77d2a2d85211017536558c055b6f904eb38f21e2dc/av-7.0.1.tar.gz#sha256=fb13afa8967d112f3f78ee6ded1082546c32462dfdfa8dac81c9539f5bda0a83
Best match: av 7.0.1
Processing av-7.0.1.tar.gz
Writing /tmp/easy_install-2ogmb6kk/av-7.0.1/setup.cfg
Running av-7.0.1/setup.py -q bdist_egg --dist-dir /tmp/easy_install-2ogmb6kk/av-7.0.1/egg-dist-tmp-fjjwaqb4
writing build/temp.linux-x86_64-3.7/include/pyav/config.h
src/av/stream.c: In function ‘__pyx_f_2av_6stream_6Stream__init’:
src/av/stream.c:3012:15: warning: assignment discards ‘const’ qualifier from pointer target type [-Wdiscarded-qualifiers]
__pyx_t_7 = __pyx_v_self->_codec_context->codec;
^
src/av/stream.c: In function ‘__pyx_f_2av_6stream_6Stream__finalize_for_output’:
src/av/stream.c:3698:44: warning: implicit declaration of function ‘avcodec_parameters_from_context’; did you mean ‘avcodec_free_context’? [-Wimplicit-function-declaration]
__pyx_t_8 = __pyx_f_2av_5error_err_check(avcodec_parameters_from_context(__pyx_v_self->_stream->codecpar, __pyx_v_self->_stream->codec), 0, NULL); if (unlikely(__pyx_t_8 == ((int)-1))) __PYX_ERR(0, 142, __pyx_L1_error)
^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
avcodec_free_context
src/av/stream.c:3698:99: error: ‘struct AVStream’ has no member named ‘codecpar’; did you mean ‘codec’?
__pyx_t_8 = __pyx_f_2av_5error_err_check(avcodec_parameters_from_context(__pyx_v_self->_stream->codecpar, __pyx_v_self->_stream->codec), 0, NULL); if (unlikely(__pyx_t_8 == ((int)-1))) __PYX_ERR(0, 142, __pyx_L1_error)
^~~~~~~~
codec
error: Setup script exited with error: command 'gcc' failed with exit status 1
##
But I have installed 'av' by **conda install av -c conda-forge**.Could you please give some advices?