Trying whisperX

How I converted a video into a transcript.

As part of making the first episode of Design Lab, I needed two assets: subtitles and a transcript.

Problem #

The entire episode was recorded with Google Meet (video + transcript), but the resulting Google Doc was not that great. YouTube's automatic captions weren't that great either.

Possible Solution #

Shalev NessAiver pointed me at whisperX which can do all kinds of transcription tasks. He had warned me that speaker diarization (figuring out who is speaking) was super slow. So I figured I could run the process over night to try it out.

Setup #

First, I had to get a HuggingFace token and agree to a bunch of user agreements.

Then, I was able to get it running on my M1 pretty easily:

git clone https://github.com/m-bain/whisperX.git
cd whisperX
pip install torch torchvision torchaudio
pip install -e .
whisperx --help

I extracted the audio from the recording:

ffmpeg -i video.mp4 audio.mp3

Running #

Then I made a little wrapper around whisperx in a file called run.sh:

#!/usr/bin/env bash
time whisperx \
  --model large-v2 \
  --compute_type float32 \
  --language en \
  --diarize \
  --min_speakers 2 \
  --max_speakers 2 \
  --threads 10 \
  --hf_token <REMOVED> \
  $@

Then I ran run.sh audio.mp3 which ran for many hours. I added the time command afterwards because I realized I didn't know how long it actually took. Certainly over 3 hours for an hour-long audio.

Clean up #

whisperx produces several formats:

.json: very detailed word-level segment information including the speaker and a score
.srt: a subtitle file. This is the main thing I cleaned up
.tsv: start, end, and text in a tab-delimited format
.txt: all the text without speaker or time information
.vtt: similar to the .srt, but starts with WEBVTT (not sure how else its different)

There were only a few places where I needed to clean up the .srt. Transcription was really good and only picked the wrong word when I was mumbling or using technical jargon (e.g., document.createElement).

Diarization was remarkably good, but it turned out that --max-speakers was technically false because there was a very short bit where my niece chimed in. It didn't mess things up too much. There were maybe a handful of places where the speaker was incorrectly selected or not indicated at all.

Overall, I was able to watch the video at 1.6x and comfortably read the subtitles along and make edits which was great. I uploaded the new .srt file to YouTube and was glad when it accepted the result without complaint.

Transcript #

The last bit was to create a transcript from the .srt file. My initial idea was to merge adjacent subtitles if they had the same speaker. I published srt2txt.py as a small gist to try it out.

The walls of text are ugly, but it made a reasonable transcript which is great for a first pass. The whole thing made me realize how inarticulate one seems when transcribing their thought process.