replace AVCodec * with const AVCodec * to read codec information

[developer0hye]

Thanks for writing the great tutorial!

I found some problem having been following your code.

The return type of avcodec_find_decoder is changed Avcodec* to const AVCodec*.

https://github.com/FFmpeg/FFmpeg/blob/master/libavcodec/codec.h#L266

[developer0hye]

@leandromoreira

Could you review this PR?

The official example code also uses const*.

https://github.com/FFmpeg/FFmpeg/blob/master/doc/examples/decode_video.c#L86

[leandromoreira]

Thanks @developer0hye did you test using the current docker ffmpeg image to see if everything works fine?

[developer0hye]

@leandromoreira Sorry, I didn't check it with current docker ffmpeg image. After checking it, I will tell you about it.

[leandromoreira]

ffmpeg

Thank you :)

[AndreiCherniaev]

The return type of avcodec_find_decoder is changed Avcodec* to const AVCodec*.

I have the same commit please check.