Animated plots, hook_ffmpeg_html and video format

[basille]

Since knitr 1.3, animated plots using hook_ffmpeg_html uses OGG video flies instead of MP4. I think it is a sensible default (although WebM would be equally good, according to browser support. However, would it be possible to have the file type as an option, so that people could, if needed, switch to MP4?

It might be already possible, in which case I apologize: I couldn't find a way to do it. As far as I understand it, the file type is hard-coded in hook_ffmpeg_html:

mov.fname = str_c(sub(paste(fig.num, "$", sep = ""), "", 
    x[1]), ".ogg")

After a couple of trials, I couldn't find a way to do it manually. For instance, modifying directly hook_ffmpeg_html using:

knit_hooks$set(hook_ffmpeg_html = function(x, options) 
    ...
    mov.fname = str_c(sub(paste(fig.num, "$", sep = ""), "", 
        x[1]), ".mp4")
    ...

does nothing: output is still a OGG file. Or setting up a new hook_ffmpeg_html_mp4, which would be called by opts_knit$get(animation.fun = hook_ffmpeg_html_mp4), results in an error. In the end, I'm not too sure what to modify or what option to change to make this choice possible.

By the way, I'm using knitr 1.5.
Mathieu.

[yihui]

Thanks for the feedback. The animation support in HTML was not carefully designed, and there is a lot of room for improvement. I do not really want to hard-code the video format. Perhaps I can clean up the mess in knitr 1.7.

[basille]

Admittedly, I'm not a video expert, but I would think that the more control given to the user the better (given sane default settings for those who don't want to bother with details, and just want an out-of-the-box result). So, in advance, thanks for taking care of the code about videos!

[yihui]

I added an internal function so you can define your own video format, e.g. if you want mp4:

knitr::opts_knit$set(animation.fun = function(x, options) {
  knitr:::hook_ffmpeg(x, options, '.mp4')
})

Note the default video format has been changed to WebM in the latest version of knitr.

[basille]

Thanks Yihui, that looks great! Looks like I have everything I was hoping for there (not tested yet).

[yihui]

FYI, I just added a chunk option ffmpeg.format so you can easily change the video format from the default webm to mp4 by using the chunk option ffmpeg.format = 'mp4'.

[basille]

Hey Yihui,

This looks great! Did the new option make it to v1.11? I couldn't have it work, with e.g. ffmpeg.format = "mp4". Shall I use the dev version instead?

In addition, does the option allow to change other settings, or is it necessary to go through opts_knit$set/hook_ffmpeg for detailed settings?

Thanks for your work!
Mathieu.

[yihui]

@basille It is in the development version: https://github.com/yihui/knitr/blob/master/NEWS.md (1.12 is not released yet) This option does not allow you to change any other settings.

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