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

If the input is audio, transcribe it with OpenRouter using openai/gpt-4o-audio-mini and the input_audio format.
If the input is video, first extract a separate audio file with ffmpeg, then transcribe that extracted audio with OpenRouter.
Save the transcript locally as a plain text file and use that saved transcript for the rest of the lecture-notes workflow.
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
...
```

lecture-notes