[whatwg] Interpretation of video poster attribute

Philip Jägenstedt philipj at opera.com
Mon Jun 9 09:01:21 PDT 2008

Hi again,

http://lists.w3.org/Archives/Public/public-html/2007Oct/0108.html it is
clear that the intention of the poster attribute is to represent a still
image from the video. This should probably be made explicit in the spec
with something in the style of:

The poster image typically represents a still frame of video. User
agents must (may?) take this into account by applying the same rules as
for rendering video (aspect ratio correction, scaling, centering). HTTP
4xx and 5xx errors (and equivalents in other protocols) must (may?)
cause the user agent to ignore the poster attribute.

This needs to be clear as there are two quite natural interpretations of
what kind of image "the user agent can show while no video data is
available". The first is an unscaled, centered "click to play" button,
while the second is a scaled, centered and aspect ratio corrected still
frame from the video.


On Tue, 2008-06-03 at 10:00 -0500, Tab Atkins Jr. wrote:
> On Tue, Jun 3, 2008 at 7:36 AM, Philip Jägenstedt <philipj at opera.com>
> wrote:
>         Hi!
>         I'm a bit puzzled about how to interpret the poster attribute
>         on
>         HTMLVideoElement:
>         "The poster attribute gives the address of an image file that
>         the user
>         agent can show while no video data is available. The
>         attribute, if
>         present, must contain a URI (or IRI)."
>         Is the intention that this image should be stretched to the
>         size of the
>         video element, or that it should be centered in the frame? If
>         the width
>         and height attributes are not given, should the video element
>         initially
>         be given the size of the poster image, or should the user
>         agent wait
>         until it has the dimensions of the video (thereby making the
>         poster
>         useless)?
>         In short, what is the intended use of poster?
>         -- Philip Jägenstedt
> Just for similar-implementation-ideas, flvplayer simply aligns the
> poster image to the upper-left of the object element, with no scaling
> at all.  If width and height are not given, it simply doesn't display
> at all.
> Unless there's already some alternate intent, I suggest <video> scale
> to the poster's size if no explicit size is given.
> ~TJ

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