MATLAB: How to get the audio signal from a video

audio processing

I have a video, i needed to get the audio signal from the video…
I did as,
a = audioread('audio1.avi');
in some cases i can read the audio, but in some cases it is showing error such as
Error using audioread (line 88)
The file type is not supported
Error in demo_audio (line 5)
a = audioread('audio1.avi');
In some videos it shows the error as
Error using audioread (line 88)
Failed to initialize internal resources.
Error in demo_audio_extract (line 9)
input_file = audioread('audio1.avi');
Is there any other way to get the audio signal from a video… why does this error occur?
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