Fix audio/webm files

[kiskoza]

Hi. Recently I encountered a bug using Active Storage when I recorded some audio in a Chrome browser (only supported mimetype is audio/webm), uploaded it to the server and got it back as video/webm - which broke the frontend logic to show it in an audio player instead of a video player. During my investigation I found this gem and noticed that it doesn't know anything about audio/webm.

In the WebM Project docs, you can find the following information:

• MIME-type: video/webm
• Audio-only MIME-type: audio/webm
• Video codec: The Codec ID SHOULD be "V_VP8" or "V_VP9".
• Audio codec: The Codec ID SHOULD be "A_VORBIS" or "A_OPUS".

That means a video webm file should contain at least one video stream (but don't need to check for audios) and an audio webm file should contain at least one audio stream (but should not have any video streams - this rule should be after the video's). I added these rules to the tables.rb file with a new sample file for audio/webm

Is there anything else I need to add regarding these changes?

[gmcgibbon]

The tables.rb file is generated using the XML data files in the repo. We recently switched from Mimemagic to Apache Tika. It seems audio/webm isn't a type Tika knows about. Could you please add the mime info to data/custom.xml and regenerate the file (using bundle exec rake tables)? Thanks!

[kiskoza]

Thanks for the feedback, I added my changes to custom.xml and regenerated the tables (got the same result, but the new line for audio/webm moved to the audios) and force pushed all of it in one commit.

We should mention this rake task in a contribution guide to help future contributors, it was easier to make the changes there now I'm aware of this file 😄

[gmcgibbon]

Looks great, thanks!

We should mention this rake task in a contribution guide to help future contributors, it was easier to make the changes there now I'm aware of this file 😄

Yes, totally agree. I will look at adding this.

[ClearlyClaire]

This seems to break some webm files, for instance this one, presumably because the V_VP8 string appears after 4096 bytes.

[kiskoza]

hi @ClearlyClaire . thanks for raising this issue. I think we should scan the whole file for the signatures as the webm's container format doesn't have a strict order for the contained streams.

@gmcgibbon what do you think? is there a way to scan the whole file?