Ok -
1) In this post, you don't refer ANYTHING to why you wanted to make AVIs - I assumed it was because you wanted to play the video files.
2) Also in this post, you don't ask ANYTHING about how to burn to dvd with srt subtitle files - you do ask that in another post, but I didn't read and reply to it until I had already read and replied to this post.
So - I'd suggest, when you want to do something specific - like in this case, take an MKV, extract video, audio and subtitles then burn them to a video DVD - ask it as a single question with a title like "How can I take a .mkv with subtitles and convert it to a video DVD?" that way you have the entire question you want answered in one post - and so you won't get half answers when people think they are answering your question, or offering potential alternatives. As well as, when you make a response like you did, people don't sit there scratching their head wondering why your responding that way with regard to what's been offered and your original question.