File read correctly by Chrome (and WebPDemux) but fails with webpmux (and WebPMux)

[GoogleCodeExporter]

What steps will reproduce the problem?
1. Open attached file with webpmux -info

What is the expected output? What do you see instead?
Error message "Failed to create mux object from file"

What version of the product are you using? On what operating system?
0.4.3 on Linux/OS-X

Please provide any additional information below.
The file was created via ffmpeg. Chrome plays correctly and WebPDemux is able 
to traverse frames correctly, but 
WebPDemux fails.

Original issue reported on code.google.com by tal.lev...@gmail.com on 30 Sep 2015 at 9:59

Attachments:

• animated.webp

[GoogleCodeExporter]

This is, in fact, and invalid file.
The VP8X chunk in the file has 'Alpha bit' set, but none of the frames contain 
transparency information.

If you look at the spec 
(https://developers.google.com/speed/webp/docs/riff_container?hl=en#extended_fil
e_format):

<Quote>
Alpha (L): 1 bit
Set if any of the frames of the image contain transparency information 
("alpha").
<Unquote>

The WebPDemux library is just being tolerant about it, but WebPMux library is 
strict and rejects the file as invalid.

This is actually a problem with ffmpeg's WebP muxer code: it always sets alpha 
bit to be true (regardless of whether any frames contain transparency), which 
is wrong.
Please file a bug on ffmpeg.

Original comment by urv...@google.com on 30 Sep 2015 at 4:51

• Changed state: Invalid

[GoogleCodeExporter]

Reported the issue on ffmpeg mailing list: 
http://ffmpeg.org/pipermail/ffmpeg-devel/2015-October/179955.html

Original comment by urv...@google.com on 1 Oct 2015 at 8:03