Loader node drops frames

Interesting observation... when using a loader node with H264 footage (.mov created by Resolve), I almost always get render errors and the render fails before all frames are processed.

The loader node complains about being unable to load frames or even that the file (which it has already loaded 100 or so frames from) no longer exists.

This only happens with H264 format video so I think Fusion is broken in this respect. Perhaps it's just not able to decode and encode H264 at the same time?

It's not hard to transcode my H264 stuff to another format (since the other supported formats work just fine and don't give this error)

I guess it's just me then. Oh well, at least I'm "special"

As youre using the term Loader node, I assume youre using Fusion inside Resolve.

You should always work in frames instead of video, as some codecs (as you're experiencing) don't store frames directly, but rather at keyframes and interpolates. This causes it to have to re-generate frames when you scrub around and sometimes it misses how its indexed. (also the reason why playing backwards on web codecs like h264 and 5 is almost always stuttery)

Try converting the source to frames, and all should be smooth.

From the OP's sig:

Still using Resolve 14 until 15 is sorted, Fusion 9 Studio

So I think he's referring to Fusion standalone. (your advice still applies though :-p)

As youre using the term Loader node, I assume youre using Fusion inside Resolve.

So I think he's referring to Fusion standalone. (your advice still applies though :-p)

Resolve 15.1's new Fusion page Loader node addition supports image formats and does not allow access to encoded movie files. That means I'm 100% confident the OP is referring to Fusion Standalone, too.

Yes, I'm using Fusion 9 stand-alone Studio version.

It seems odd to me that there should be this limitation, even for a format like H264 since the codec should simply be spitting out the next frame when requested. If I run the timeline without a saver node, everything is fine -- but if I connect a saver node, then the loader node drops frames so something is odd.

The thing is - as I understand h264 codecs, that there is no such thing as a 'next frame' - it's a differential format with some pieces of the next frame coming from 10 frames ago, so it's not designed for random acccess of frames. What are your 'frame at once' settings in the preferences? This could definitely influence those results: if Fusion is working on 2 (or more) frames concurrently and needs to save them randomly, this can happen. If this still happens if you work with image sequences then something is really wrong, for now, this is something that's annoying, but can be expected with h264 (and other compressed) codecs.

Since reading the frames is a sequential operation, it is not difficult for the codec to honour a "next frame" request.

The fact that the loader node works 100% fine when the saver node is not enabled shows that it does actually do this as expected.

However, when the saver node is enabled, things go to hell in a handbasket -- which suggests that there's some problem associated with decoding and encoding at the same time -- perhaps a re-entrancy issue with a shared codebase.

If it was simply the fact that H264 has P frames that are dynamically reproduced when decoding then the loader node would fail all the time -- wouldn't it?

I'm no expert, so I'm not sure. But if you're working interactively Fusion renders stuff out differently than on full renders. So if you don't jump back and forth all the time, the loader works sequentially.
And yes, my loaders fail regularly before I add a saver to my comp. Well, they don't actually *fail* but they display error messages and then load the desired frame anyway. Sometimes setting the loader option to 'wait' helps as well. But I think your assessment that decoding and encoding are in each other's way might be worth investigating. If you save to frames instead of a codec, does it still fail?