zznidar/lecture-speedrun

Speed up silent portions of a lecture video/audio on-the-fly! Lecture Speedrun. Prototype. Inspired by jumpcutter.

lecture-speedrun

Lecture Speedrun. Prototype. Very experimental. Accessible here: https://zznidar.github.io/lecture-speedrun/

Inspired by carykh's Automatic on-the-fly video editing tool! and jumpcutter.

Very experimental

Prototype tested only in Firefox and Chrome. Firefox prior to v91 may not play any audio.

What is Lecture Speedrun?

Lecture Speedrun allows you to speed up silent portions of a lecture video/audio on-the-fly, saving you precious time. Should it happen that your teacher speaks really slowly or makes a lot of pauses between sentences, use Lecture Speedrun to play the silent portions at a higher rate.

Usage

1. Open https://zznidar.github.io/lecture-speedrun/ in Firefox or Chrome.
2. Pick a video or audio file of the lecture you want to speedrun.
3. Optionally adjust settings.
4. Play the video.

Settings

Confirm your settings changes with the Confirm button.

Loudness threshold

How loud the audio should be at a given moment to be treated as speech. Observe Current loudness below to fine-tune it. If silence is treated as speech, increase the threshold. If speech is treated as silence, lower the threshold.

Smoothen

How many consequent analyses should be silent to count it as silence. The higher this number, the longer it will take after the lecturer stops speaking to start fast-forwarding.

Speed of silence

Playback speed when the lecturer is silent.

Speed of speech

Playback speed when the lecturer is speaking.

Lefting (revert each start of speaking)

Experimental feature to seek the video back for a split-second once the lecturer starts speaking. Would be useful if the first sounds of speech were cut off. Doesn't work too well 😅

Audio gain

Increase the playback loudness. Useful if the video volume is very low. Note that this does not affect the analysis.

Hide current loudness indicator

Current loudness is shown at every given moment to make it easier for you to adjust the Loudness threshold. However, some users reported it uses a lot of their CPU. Check this box to stop updating current loudness indicator.

Hide speed indicator

This icon indicates when the video is fast-forwarded: ⏩︎ Check this box to stop indicating the state of speed.

Troubleshooting

• Make sure not to use the lefting functionality. It really does more harm than good.
• Some users report better performance if they disable Hardware-accelerated video decode and Hardware-accelerated video encode under chrome://flags
• Firefox limits playback speed to 4x.

Note

Binge-watching your lectures at 2x playback speed on your sofa with a glass of beer and a bowl of popcorn in your hands during the last 2 weeks before your exams might not be the best idea.

lecture-speedrun's Issues

Changing smoothing while playing sometimes causes Lecture Speedrun to stop working

In some cases, it happens that chaning the "Smoothen last n samples" setting while a video is playing causes Lecture Speedrun to break.

More precisely, it happens when you decrease that number. Apparently the indexSmoothing variable is not reset when updating settings. That means that it may happen that current loudness gets written into the array at some out-of-bound index (which apparently extends the array, creating something like [0.16436233363224984, 0.13041777660688667, empty × 39, 0.17346392315239798]).
However, in the subsequent line the index gets moduled to the new smoothing value, preventing it from reaching the last few elements of the array. Therefore, the last elements of the array may remain "loud" forever, preventing the silence from being sped up.

Possible solution: Reset the indexSmoothing variable in the updateSettings function.

Screenshare in BBB gets out of sync

Changing webcam video playback rate in BigBlueButton does not automatically change the playback rate of the screen share. Thus, they get out of sync quickly.

Affects: bbb-spedrun.js

Make this a PWA with offline support

This would allow users to watch local videos even when offline (airplane and other means of transport ...).
Once the webpage is loaded, internet connection ist sowieso not required anymore for local files.

Workaround for .mkv support

The following project successfully adds support for .mkv files from OBS to play in Firefox 106.0.2: https://github.com/ilian/mkv-web