We spotted a question online recently that we had the exact problem with a while ago. Searching didn't find an answer on Google, but we did eventually find out why the trim option wasn't available on YouTube.
Live broadcasting to YouTube is fantastic. A few years ago, broadcasting around the world would have cost tens if not hundreds of thousands of dollars. Now you can do it from your home with a laptop.
The start of live broadcasts on YouTube are not as easy as you think. You'll have to wait whilst checking everything is working and possibly post the video on websites and social media to entice more views. There are two ways of getting around this false start.
The first is to run a countdown, which seems like a good idea, but is annoying as it leaves people waiting for the show to start. The second is to go live, but only start the subject once ready and checked. Both can leave minutes at the top of the YouTube video and that doesn't lead to a very good viewer experience for people watching later. They need to be engaged once they have clicked.
YouTube has a handy trim tool in YouTube Studio - You will find it under the Editor heading on the left hand side of the web page. Perfect you would think to trim the front and end of a live recording?
In the image below (click for larger version) you can see our recent FCP.co Live show where we talked to Larry O'Connor from OWC about Thunderbolt 4. The video needs a trim at the top and end, but YouTube is only offering a 'Save as New' option in the top right corner.
Saving as new will make a new YouTube video ID and listing, which you really don't want to do as the video has already been embedded on websites and linked & retweeted many times on Twitter.
The giveaway for the trimming restriction here is the blue bar. Quite simply, YouTube hasn't finished processing the recording! Sometimes I have to wait overnight for the timeline to be populated with images.
When that happens, you can trim away to produce a video on the same YouTube video ID. In the image below you can see I've slid the front trim marker up to the point where I want the new beginning of the video. The slider on the right gives you access to enlarge the timeline to see the waveforms for greater accuracy. This enables you to start right before a word like 'Hello" for example..
But the Save button is greyed out! You have to hit the Preview button at the bottom of the frame, then then the Save button will become clickable.
The Save button will turn blue and once pressed will trim the video or take any snips, blurs or audio muting you've done on the timeline. If you've had any copyright strikes, you are probably very familiar with this process.
This trim can take some time, I have had to wait for up to 24 hours for it to be processed. Although YouTube's dialogue box says the untrimmed video will still be available, I have had occasions where the whole video has gone offline. My advice would be do the trim when you expect low traffic for the video.
If you watch the trimmed & processed video back and spot a mistake, you can revert to the original length and start the process again. The 'Revert to Original' option becomes available if you click on the three dots on the right hand side.
One gotcha here. If you do a trim and save, you will lose all the live comments from the original stream. That might be bad, but having a video start at exactly the right place when somebody clicks is a price worth paying.