LectureSift · Study by exam and topic
How to study a long lecture recording, section by section
Split a two-and-a-half-hour lecture recording at its topic changes: a time index, one sentence and one question per section, and a parking list.
No account needed for the guest trial · Current limits are shown in the workspace and on the Plans page
Why a long recording should not be studied in one go
Studying a two-and-a-half-hour lecture recording by watching it from start to finish takes a long time and is hard to concentrate on. If you stop halfway, it is difficult to find where to pick up again, and when you want to revise one topic before the exam, you will not remember where in the recording it came up. Reading an hour's worth of notes in one sitting is hard enough; nobody can be expected to hold a two-and-a-half-hour talk in their head as a single piece.
This guide suggests splitting a long recording into sections at its topic changes and writing a short index row for each one. The index works like a table of contents for the recording: it shows which topic starts at which minute, the main point of that section and a question to ask yourself. Once the sections are marked, you can use the Cornell note-taking method to work through each one on its own page; this guide is about dividing the recording rather than the notes themselves.
Four steps to dividing a recording
- Mark the topic changes. Note phrases such as “Let's move on to…” or “That's it for this topic”, a new slide title, or a long break as transition points. Skimming the transcript to find them is quicker than watching the recording.
- Give each section a title. The title should say what the section covers: write “Ionic bonding”, not “Part 2”. Mark breaks and announcements too, so you can skip them when you revise.
- Write one sentence and one question per section. The sentence gives the section's main point; the question picks out something from it that could come up in the exam. If you cannot write the question, you may not have understood the section yet.
- Keep a parking list. Write down anything the lecturer mentioned without explaining, or that you did not follow, on a separate list. You clear it with the textbook, a teaching assistant or the next lecture.
Example: a two-and-a-half-hour general chemistry lecture
This section is an example. The lecture index, questions and parking list were written for this guide for teaching purposes. They are not taken from a student's upload or from a live LectureSift output; check the chemistry against your own textbook.
Lecture index
| Time | Section | One sentence | Question to ask yourself |
|---|---|---|---|
| 00:00–00:12 | Introduction and recap of last week | Electron configuration and valence electrons were revisited. | — |
| 00:12–00:41 | Ionic bonding | Oppositely charged ions formed by electron transfer attract each other. | Between which atoms does ionic bonding usually form? |
| 00:41–01:10 | Covalent bonding and Lewis structures | Atoms share electrons; a Lewis structure shows bonding pairs and lone pairs. | How are lone pairs shown in a Lewis structure? |
| 01:10–01:20 | Break | — | — |
| 01:20–01:52 | Electronegativity and polarity | A difference in electronegativity makes a bond polar; whether the molecule is polar also depends on its shape. | Can a molecule with polar bonds be non-polar? |
| 01:52–02:25 | Intermolecular forces | London forces, dipole–dipole interactions and hydrogen bonding were compared. | When does hydrogen bonding occur? |
| 02:25–02:30 | Announcements | The assignment deadline was announced. | — |
Parking list: around 01:05 the lecturer briefly mentioned resonance without explaining it; look it up in the relevant textbook chapter. Reread the boiling-point comparison from around 02:10 in the transcript.
Question
The C=O bonds in CO₂ are polar. Why is the molecule non-polar? A) There is no electronegativity difference between C and O · B) The molecule is linear, so the two bond dipoles cancel · C) CO₂ has no covalent bonds · D) The oxygen atoms have no lone pairs
Show the answer and explanation
B) Oxygen is more electronegative than carbon, so the C=O bonds are polar. But CO₂ is linear: its two bond dipoles are equal in size and point in opposite directions, so they cancel. Compare H₂O, which is bent because of the two lone pairs on oxygen; its dipoles do not cancel, and the molecule is polar. A and C are simply untrue, and so is D: the oxygen atoms in CO₂ do have lone pairs.
Short answers to the index questions
Ionic bonding: usually between a metal and a non-metal with a large difference in electronegativity. Lewis structures: lone pairs are drawn as pairs of dots around the atom's symbol. Polarity: yes; as with CO₂, bond dipoles can cancel. Hydrogen bonding: between a hydrogen atom bonded to F, O or N and a lone pair on an F, O or N atom in a neighbouring molecule.
Flashcards
Does a molecule's polarity depend only on the polarity of its bonds?
No. Its shape matters too: in CO₂ the bond dipoles cancel; in H₂O they do not.
What goes in each row of a long recording's index?
The time range, a section title, one sentence giving the section's main point, and a question to ask yourself about it.
Using LectureSift with a long recording
You can upload a lecture recording as MP4, MP3, WAV or MOV. Before uploading a long one, check your plan's limits. According to the plans page, a free account gives you 120 minutes each month, and a single job can be at most 60 minutes long and contain up to 3 sources. Paid plans allow longer jobs and more files per job. Within those limits, a whole two-and-a-half-hour recording is more than a free account's monthly minutes.
- Split at topic changes. If you have to cut the recording into parts, cut at the topic changes in your index rather than at arbitrary minutes. That way each pack covers a single topic.
- Keep track of timestamps. If you add several files to one job, the timestamps continue from one file to the next in the order you added them; in separate jobs, each recording starts at 00:00. Putting each part's start time in the original lecture into its file name makes it easier to match against your index.
- Consider an audio file for a large video. If a video file is over the upload limit, you can upload just its audio as MP3. Slide images cannot be taken from video frames in that case.
- Turn on precise timestamps. The “Precise timestamps” option shows speech segments with more precise times, which makes topic changes easier to find; it can make processing take longer.
- Go back with “Ask this lesson”. When you ask something like “What example did the lecturer use for hydrogen bonding?” on the results screen, the answer comes only from that lesson's summary, notes and transcript, with the supporting timestamps shown.
Your original file is deleted when processing ends, even if processing fails; if that deletion fails, the file is removed with the lesson when the lesson is deleted or expires. LectureSift is therefore not a backup of the recording, so keep your own copy if you will need it again.
Frequently asked questions
What is the quickest way to find topic changes?
Skim the transcript. Phrases such as “now”, “let's move on” or “the next topic”, and long pauses, usually mark a change. In lectures with slides, a new slide title is another good sign.
What should I use to cut the recording?
LectureSift does not split the recording for you. You can cut it at the topic changes in your index with a video or audio editing app on your device.
Should I upload the break and the announcements?
If you are splitting the recording yourself, cutting out a long break saves minutes. For announcements, a separate note is usually enough.
Can I combine this with Cornell notes?
Yes. You can start a separate Cornell page for each section of the index and move the questions from the “Question to ask yourself” column into the left-hand question column of the page.
Can I try it for free?
Yes. Without an account, a one-time guest trial processes a source of up to 30 minutes. A free account gives you 120 minutes each month. With a long lecture, try a single section first.
Try it with your own recording
Start with one section.
Upload the part of your long recording that covers one topic as a guest. Find the topic changes in the transcript and write the first rows of your index.