Lecture Notes

Lecture Notes Skill

Transform lecture materials into structured, exam-ready Markdown notes for Obsidian.

Audio and Video Inputs

When the source material is an audio or video file, always create a local transcript first and use that transcript as the primary input for note generation.

Required Workflow

1. If the input is audio, transcribe it with OpenRouter using openai/gpt-4o-audio-mini and the input_audio format.
2. If the input is video, first extract a separate audio file with ffmpeg, then transcribe that extracted audio with OpenRouter.
3. Save the transcript locally as a plain text file and use that saved transcript for the rest of the lecture-notes workflow.
4. If useful, also save the raw JSON response locally, but the .txt transcript is the canonical note-generation source.

OpenRouter Audio Transcription

Before using audio or video transcription, make sure OPENROUTER_API_KEY is defined in the environment.

Use OpenRouter's chat completions API with multimodal input_audio. The prompt should explicitly ask for a verbatim transcript with minimal cleanup.

AUDIO_BASE64=$(base64 < "Lecture 05.audio.wav" | tr -d '\n')

curl https://openrouter.ai/api/v1/chat/completions \
  -H "Content-Type: application/json" \
  -H "Authorization: Bearer $OPENROUTER_API_KEY" \
  -d "{\n    \"model\": \"openai/gpt-4o-audio-mini\",\n    \"messages\": [\n      {\n        \"role\": \"user\",\n        \"content\": [\n          {\n            \"type\": \"text\",\n            \"text\": \"Transcribe this lecture audio as plain text. Keep the wording faithful to the speaker, preserve important structure, and do not summarize.\"\n          },\n          {\n            \"type\": \"input_audio\",\n            \"input_audio\": {\n              \"data\": \"$AUDIO_BASE64\",\n              \"format\": \"wav\"\n            }\n          }\n        ]\n      }\n    ]\n  }"

For actual skill usage, save the JSON response first, then extract the transcript into a plain text file:

AUDIO_BASE64=$(base64 < "Lecture 05.audio.wav" | tr -d '\n')

curl https://openrouter.ai/api/v1/chat/completions \
  -H "Content-Type: application/json" \
  -H "Authorization: Bearer $OPENROUTER_API_KEY" \
  -d "{\n    \"model\": \"openai/gpt-4o-audio-mini\",\n    \"messages\": [\n      {\n        \"role\": \"user\",\n        \"content\": [\n          {\n            \"type\": \"text\",\n            \"text\": \"Transcribe this lecture audio as plain text. Keep the wording faithful to the speaker, preserve important structure, and do not summarize. Return only the transcript text.\"\n          },\n          {\n            \"type\": \"input_audio\",\n            \"input_audio\": {\n              \"data\": \"$AUDIO_BASE64\",\n              \"format\": \"wav\"\n            }\n          }\n        ]\n      }\n    ]\n  }" \
  > "Lecture 05.transcript.response.json"

jq -r '.choices[0].message.content // (.choices[0].message.content[]? | select(.type == "text") | .text)' \
  "Lecture 05.transcript.response.json" > "Lecture 05.transcript.txt"

Recommended Local File Outputs

Given an input file like Lecture 05.mp4 or Lecture 05.m4a, save derived files alongside it using predictable names:

• Lecture 05.audio.wav for audio extracted from video or normalized for upload
• Lecture 05.transcript.response.json for the OpenRouter API response
• Lecture 05.transcript.txt for the plain text transcript used to generate notes

Video to Audio Extraction

Use ffmpeg to extract audio from video before transcription. A safe default is:

ffmpeg -i "Lecture 05.mp4" -vn -ac 1 -ar 16000 -c:a pcm_s16le "Lecture 05.audio.wav"

If the source is already audio but not in a convenient format, normalize it to .wav before base64 encoding and upload.

Transcript Handling Rules

• Always generate notes from the saved local transcript file, not directly from the raw media file.
• If the user also provides slides, PDFs, or other lecture materials, combine them with the transcript when producing notes.
• Preserve important spoken structure such as section transitions, definitions, theorem statements, examples, and repeated exam hints.
• If the transcript is clearly noisy or incomplete, note uncertainty in the final notes rather than silently inventing missing content.
• If a transcript already exists locally for the same media file, reuse it unless the user explicitly asks for a fresh transcription.

Output Format

Output all notes inside fenced codeblocks. When content spans multiple chapters or distinct topics, create separate files.

File Naming

Chapter X - Title.md or Unit X - Title.md

Document Structure

---
course: [Course name if known]
lecture: [Lecture number/title]
date: [Date if provided]
tags: [relevant, topic, tags]
---

# Title
Brief overview connecting to previous material when applicable.

## Key Concepts
Bulleted summary of the most important takeaways.

## [Content Sections]
Organized by topic from the source material.

## Definitions
New terms introduced in this lecture.

## [Additional Sections as Needed]
Examples, proofs, diagrams, etc.

Formatting Rules

Headings

No empty lines after headings. Content begins immediately on the next line:

## Section Title
Content starts here directly below the heading.

Math and Equations

Use LaTeX inside $...$ (inline) or $$...$$ (block):

The quadratic formula is $x = \frac{-b \pm \sqrt{b^2 - 4ac}}{2a}$.

$$
\int_0^\infty e^{-x^2} dx = \frac{\sqrt{\pi}}{2}
$$

Footnotes

Use Markdown footnotes for supplementary information. Never use citations:

This concept was introduced in 1905[^1].

[^1]: Additional context or clarification here.

Callouts for Exam-Important Content

Use Obsidian callouts to flag critical information:

> [!important] Exam Alert
> This formula is frequently tested.

> [!note] Remember
> Supplementary context or tips.

> [!example] Worked Example
> Step-by-step demonstration.

> [!warning] Common Mistake
> Students often confuse X with Y.

> [!definition] Term
> Formal definition here.

Wiki-Links

Use [[double brackets]] to link related concepts:

This relates to [[Chapter 2 - Thermodynamics#Entropy]].

Content Guidelines

Completeness

Capture all information from source material, especially:

• Formulas and equations
• Definitions and theorems
• Examples and worked problems
• Diagrams (describe or recreate in text/ASCII if needed)
• Any content emphasized as important by the lecturer

Definitions Section

Always include a ## Definitions section. Format each term:

## Definitions
**Term**
Precise definition immediately below.

**Another Term**
Its definition here.

Connections

When possible, reference previous lectures or related concepts:

## Key Concepts
- Builds on [[Chapter 3 - Kinematics]] by introducing forces
- Extends the velocity equations to include acceleration

Examples

Preserve all examples from source material. Format with the example callout:

> [!example] Finding the Derivative
> Given $f(x) = x^3 + 2x$, find $f'(x)$.
>
> **Solution:**
> $$f'(x) = 3x^2 + 2$$

Multiple Files

When source material covers multiple distinct chapters or units, output each as a separate codeblock with clear file naming:

```markdown
<!-- Chapter 1 - Introduction.md -->
---
course: Physics 101
...
```

```markdown
<!-- Chapter 2 - Mechanics.md -->
---
course: Physics 101
...
```