Issues with rendering

Hi, I’m new here & fairly new to Natron. Recently I’ve been having issues rendering my projects. Whenever I use the Write to render, it takes ages and the video ends up displaying a black screen.
I’m using the Container named MP4 (MPEG-4 Part 14) [mp4] and the Codec named H264 Cisco libopenh264 H.264/MPEG-4 AVC encoder [libopenh264].
These were working fine for a few projects and producing MP4 videos in only a couple of minutes. I’m now waiting between 15-30 minutes… for a black screen.
I’ve compared the projects which do still render properly and the new ones that don’t & have noticed one difference. The projects that render work have R G B A boxes ticked at the top of the Write & the ones that display black screens don’t have these tick boxes.
I hope this is a simple fix & hope someone here can help.
Thanks in advance, David.Screen Shot 2021-05-19 at 15.55.23 Screen Shot 2021-05-19 at 15.55.36

how is you alpha channel looking before you write it out?

Where am I finding the alpha channel? Soz amateur lol

in the top left there is a drop down to choose the channel you are viewing or press a. Make sure the Alpha is white. If it is black you are rendering a full transparent image. Since h264 is not capable of alpha it will be just black. Also maybe consider writing to png first and then convert it to h264. Your more flexible that way. Have more controll on compression etc.

I pressed a to find it & the Alpha was white. It’s rendering now, so will let you know when it’s done & if that worked.
If I write to png first, how do I then convert it to h264?
Also, would you know why the rendering has slowed down so much? I am making longer projects with more going on, but I’ve even tried rendering short projects with not a lot going on & it just seems a lot slower than when I first started using the program. It will start running at like 13 minutes, then drop to around 8, then creep up to around 15 minutes. But it actually takes much longer than 15 minutes.

It has finally finished rendering and to no avail. Still showing a black screen.

h264 had issues before. Use png. You can convert it useing handbreak or ffmpeg.

Thank you for your help.

Don’t use PNG.

PNG is a great format for displaying graphics with transparency on the web… And that’s pretty much it. If you’re not doing that there are much better formats to use. For any video work I recommend EXR.

If you want to get into it any more than that and not just take my words at face value, here’s an excellent stack exchange thread that breaks down different compression types and what you should use where! Either the ZIP or PIZ compression algorithms will probably give you the best results.

Thanks for the advice on the best format but I’m still recieving black screens. My issue isn’t to do with compression, I don’t think.

Can you submit a sample file? If it’s not your alpha channel and everything looks good in the viewer I’m not really sure what the issue would be…

I don’t believe it lol. The video is playing on here! Must be a problem with my quicktime/VLC.

Yeah, the png suggestion was more to debug things. I usually stick to exr.

I don’t believe it lol. The video is playing on here! Must be a problem with my quicktime/VLC.

Propably this is an issue with chroma subsampling. Try 420 instead of 422.

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