I love the concept!

Some constructive feedback, running chromium on linux:

1- The lyrics can't be selected with my mouse, making it difficult for me to use other translation tools to get a sense of what the lyrics mean.

2- Below the lyrics section, there is what looks like a blue progress bar moving from "full" on the right, then moving to "empty" on the left. I have no idea what progress this is tracking. It seems to bounce back to full after going to empty, and since each cycle appears vaguely related to the progress of the text, I assume there is some connection. However, it isn't clear.

3- There are four blue boxes below the reverse progress bar, which are mostly empty but occasionally have words in them. And if I click in the area, they adopt colors, one green and if wrong, the others red. However, it seems like the translation of the lyric that is in red matches the translation in green, and the other words in the remaining 3 boxes are red. Wouldn't it make more sense to make the lyric highlighted in green, so you can visually see that it matches the word in green? The fact that the selection is wrong can be indicated by setting the background of the answer area red, rather than making the red appear in the lyric itself.

4- The instructions only appeared on the third video I watched, the first two I either didn't see the one line instruction or it didn't appear. Probably the former, so it might make sense for the instruction line to appear for a longer period of time.

5- The text boxes move around, it would be much easier and effective for me if I could press 1 2 3 or 4 to select the appropriate box. The mistakes I've made so far are mostly getting the pointer in the correct position, rather than not knowing which is the correct translation.

6- With understanding that "everyone is a critic": I found the music selection annoying, at least in the English->French series.

7- With understanding that "I have no idea of your intended profit model": it seems very challenging to get breadth and depth in terms of the number of languages, dialects, and songs out there. One possibility that other language-learning tools have used is crowd-sourcing the data, i.e. enabling users of the site to input videos, lyrics, timings, difficulty levels, perhaps even offer ratings and corrections.

8- While linguician makes a nice adjunct to primary language learning, and I can see the charms of sharing culture along with language, and having video that may provide more cues to meaning, it seems that there is some ideal threshold in terms of comprehensibility for language learning. For example, I've heard that an ideal scenario is one at which the language learner is always in a state of roughly 90% comprehensible speech, but in linguician it doesn't seem scalable in terms of comprehensibility. Contrast this to, for example, Earworms MBT, which for a new language learner is totally comprehensible and slowly builds up.

9- Having gone through the painful adult language learning process multiple times, I feel that adding relative scores adds some way for users to feel where they are at.

10- The lyrics on the first three videos I selected took approximately 20 seconds to load, which seems a bit excessive given that 20 seconds of HD video have been downloaded by that point.

11- The progress bar, which I believe is a timeout counter for selecting the appropriate response, begins its countdown significantly before the target phrase is shown on the screen.

12- Now it appears the videos have a dual selection, "I want to know this" versus "I already know this", which probably has to do with the path taken to get to the video. This seems like somewhat of a waste of time -- either teach or test, or explain what the point is.

13- The videos say "press play on the video to start", but the videos begin playing automatically anyway.

14- Having a way to see or hide a full translation of a song may be useful to get the flavor of a song's overall meaning.

15- Not sure what the black music note in the red circle at the top right of each video is supposed to do.

16- There are multiple errors in the English translations, e.g. "they live" for "their lives" I believe, but it's very difficult to enumerate them without the ability to select text to copy and paste.

In summary: This is really a great platform, I look forward to seeing where this goes!