"repeat" loop is not recognized by Chrome

[happylinks]

I'm creating gifs with repeat: -1, which should loop. In finder this works fine, but in browsers (Chrome for example) it only plays once. I found this post about it: https://stackoverflow.com/questions/10867789/animated-gif-only-loops-once-in-chrome-and-firefox

Aparantly you need to add this extension command: "0x21,0xFF,0x0B,"NETSCAPE","2.0",0x03,0x01,0x00,0x00,0x00" for it to loop.

Is this something we can add to this library? I can make a PR, but any guidance would be great.

[fintelia]

Thanks for tracking this down! I'd be in favor of accepting a PR to fix this

[okaneco]

I looked into this and I'm not sure how to replicate it.

The number of repetitions is a u16, so the program won't compile without an integer cast. Converting from -1_iX will result in u16::MAX. An infinite loop corresponds to 0, according to http://www.vurdalakov.net/misc/gif/netscape-looping-application-extension. Perhaps Finder is automatically looping a one-repeat GIF?

pub enum Repeat {
    Finite(u16),
    Infinite,
}

https://docs.rs/gif/0.12.0/gif/enum.Repeat.html

The extension block is written when Encoder::set_repeat is called, which includes the NETSCAPE2.0 command. Either a 0 or the number of repetitions is written.

https://github.com/image-rs/image-gif/blob/442225a78d55c9deb900fc4805117db7b778d822/src/encoder.rs#L287-L297

If Repeat::Finite(0) is specified, then the block isn't written. https://github.com/image-rs/image-gif/blob/442225a78d55c9deb900fc4805117db7b778d822/src/encoder.rs#L272-L276

Here's the example program I used to generate a finite and infinite gif, then inspect the image binary data.

Create the file in the `gif/examples` folder. ```rust // loop.rs fn main() { use gif::{Encoder, Frame, Repeat}; const WIDTH: usize = 8; const SQUARED: usize = WIDTH * WIDTH; let black = [0; SQUARED * 3]; let white = [255; SQUARED * 3]; let (width, height) = (WIDTH as u16, WIDTH as u16); let mut image_finite = std::fs::File::create("./blinker_fin.gif").unwrap(); let mut image_infinite = std::fs::File::create("./blinker_inf.gif").unwrap(); let mut encoder_finite = Encoder::new(&mut image_finite, width, height, &[]).unwrap(); let mut encoder_infinite = Encoder::new(&mut image_infinite, width, height, &[]).unwrap(); encoder_finite .set_repeat(Repeat::Finite(-1i16 as u16)) .unwrap(); encoder_infinite.set_repeat(Repeat::Infinite).unwrap(); for buffer in [black, white] { let mut frame = Frame::from_rgb(width, height, &buffer); frame.delay = 50; encoder_finite.write_frame(&frame).unwrap(); encoder_infinite.write_frame(&frame).unwrap(); } } ``` You can diff the binary of the gifs with the following and see the only difference is whether `0u16` or `u16::MAX` is written. ```bash cargo run --example loop xxd blinker_fin.gif > fin.hex xxd blinker_inf.gif > inf.hex diff fin.hex inf.hex ``` ```bash < 00000020: 3003 01ff ff00 21f9 0404 3200 0000 2c00 0.....!...2...,. --- > 00000020: 3003 0100 0000 21f9 0404 3200 0000 2c00 0.....!...2...,. ^^^^^ ```

[happylinks]

Did some testing, just to be helpful.

Gif generated with this library: https://tella-static.s3.us-east-2.amazonaws.com/clfic1aqm00000gmk3leg87cr.gif

"Fixed" with ffmpeg -i <input gif> -loop 0 -c copy <output gif>: https://tella-static.s3.us-east-2.amazonaws.com/clfic1aqm00000gmk3leg87cr-fixed.gif

Hex diff:

I'm not seeing the NETSCAPE2.0 part at all in the original gif, I set repeat to -1.

I'll test your code as well.

[happylinks]

Tested your example code and it looks fine indeed, it repeats infinitely in chrome.

Maybe it has to do with the library I'm using: https://gitlab.freedesktop.org/gstreamer/gst-plugins-rs/-/blob/main/video/gif/src/gifenc/imp.rs#L120 Code looks good at first glance though. I'll dig a bit deeper.

[happylinks]

Ok yeah, it's not this project, it's the gstreamer plugin passing "0" for repeats. Sorry about the noise! I'll fix it in that package.