https://chrome.google.com/webstore/detail/video-speed-controller/nffaoalbilbmmfgbnbgppjihopabppdk
This extension is magical. It works on almost all types of video. You can speed up videos up to 4x and slow them down .5x with sound. Anything beyond those points does not have sound, but will still play video at any speed you select.
Edit: As Perkie says, this tool can alter framerate, and thus reduce accuracy in verification. For modding, use your discretion. Don't speed up videos if you can't follow gameplay or track frame specific moves. Slow back to normal or reduced speeds near splits or critical moments. Its a great tool for finding the exact last frame that ends the speedrun at low playback speed. Slowing down can also be useful for verifying that players aren't using bots -- I have used it several times for this purpose.
Being realistic, we have many mods on speedrun.com that verify non-WR runs by checking start and end times, skimming, and clicking through videos on intervals: https://www.reddit.com/r/speedrun/comments/45e1en/a_question_to_speedruncom_moderators_how_do_you/
From the reddit post, this includes:
- GothicLogic, super mod of Super Mario 64
- TonesBalones, super mod of Splatoon and Splatoon 2
- CartinaCow, super mod of DuckTales
- MopeyJoe, super mod of Mega Man X4
- TreZc0, super mod of Twilight Princess and mod of BOTW
- bonecrusher1022, super mod of Paper Mario
- QuantumTM, super mod of The Hobbit
Fun fact: Some of these mods will benefit from a tool that allows them to watch an entire run at a faster or slower pace.
This is the second most polite fistfight I've ever witnessed, but I have to award the gold medal to the conversation between Hydrogen and Boost: