I'm working on a 32x texture pack, and currently making lava. But for some reason, the flowing lava appears as 16x in game. It still uses the texture, but only part of it. The texture is 32x512. This is the lava_flow.txt
While most animations follow the above format and rules, there are a few exceptions. The two biggest are Flowing water and lava. These two files follow a special set of rules when it comes to laying out your animation sheet. Don't worry, once you understand them they're pretty easy. It's just a few extra steps.
IMPORTANT: FLOWING LIQUIDS ONLY: This only applies to water_flow.png and lava_flow.png. The still water and lava files follow the same format as any other block, as outlined above. Do NOT do the stuff in this section with your still liquids. It will end up looking really weird.
To make a flowing liquid animation, start by making your frames the same way you would any other animation. Don't organize them into strips like normal, though. Instead, take each frame and repeat it in a 2 by 2 block. This will make each frame in a flowing liquid animation twice the normal resolution of your texture pack. Don't worry, this is normal and won't affect the look of your pack at all.
Once you've done that, then you organize them into strips as shown above.
Here's a graphical representation of this:
This will also help you if you're converting your flowing water/lava animations from the pre-1.5 MCPatcher/Optifine format to the new Minecraft flowing liquid animation format.
Tip: Why the Double Tile?: If you're wondering the reason why the flowing liquid animations are different, it's because of how Minecraft renders the water textures. Flowing water tiles are placed in the middle of the 2x2 area. This saves Minecraft from having to tile the texture in real time. If your animation looks different than expected, remember that the tile is actually in the middle of your frame, and not lined up with the single tile in the corner. A 25% offset is required to fix this if it's an issue.
When making the .txt file for these animations, remember that your frames are now twice as large as they normally would be. When you go to figure out the number of frames you have, remember to divide both dimensions of your animation strip by 2 to get your 'real' resolution.
I think I will have to make this my next scripting project; same as the one I've got now, just that it tiles them too. So you could take your 16x lava animation, in a 16x16 layered file with 16 layers, and turn it into the properly sized 32x512 animation strip.