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[whatwg] HTML5 video: frame accuracy / SMPTE

From: David Singer <singer@apple.com>
Date: Tue, 11 Jan 2011 23:35:41 +0100
Message-ID: <024C63F5-8B41-423A-90F5-17B8A3163375@apple.com>
why does the frame rate make any difference on the accuracy of seeking to a time?  Imagine a video that runs at 1 frame every 10 seconds, and I seek to 25 seconds.  I would expect to see 5 seconds of the third frame, 10 seconds of the 4th, and so on.

On Jan 11, 2011, at 18:54 , Rob Coenen wrote:

> just a follow up question in relation to SMPTE / frame accurate playback: As
> far as I can tell there is nothing specified in the HTML5 specs that will
> allow us to determine the actual frame rate (FPS) of a movie? In order to do
> proper time-code calculations it's essential to know both the video.duration
> and video.fps - and all I can find in the specs is video.duration, nothing
> in video.fps
> 
> -Rob
> 
> 
> On Mon, Jan 10, 2011 at 9:32 PM, Kevin Marks <kevinmarks at gmail.com> wrote:
> 
>> If you really want to test timecode, you need to get into SMPTE drop-frame
>> timecode too (possibly the single most annoying standards decision of. all
>> time was choosing 30000/1001 as the framerate of NTSC video)
>> 
>> Eric, can you make BipBop movie for this? - Like the ones used in this
>> demo:
>> 
>> 
>> http://developer.apple.com/library/mac/#documentation/NetworkingInternet/Conceptual/StreamingMediaGuide/UsingHTTPLiveStreaming/UsingHTTPLiveStreaming.html
>> 
>> http://devimages.apple.com/iphone/samples/bipbopgear3.html
>> 
>> 
>> On Mon, Jan 10, 2011 at 11:18 AM, Rob Coenen <coenen.rob at gmail.com> wrote:
>> 
>>> Thanks for the update.
>>> I have been testing with WebKit nightly / 75294 on MacOSX 10.6.6 / 13"
>>> Macbook Pro, Core Duo.
>>> 
>>> Here's a test movie that I created a while back. Nevermind the video
>>> quality- the burned-in timecodes are 100% correct, I have verified this by
>>> exploring each single frame by hand.
>>> 
>>> 
>>> http://www.massive-interactive.nl/html5_video/transcoded_03_30_TC_sec_ReviewTest.mp4
>>> 
>>> Please let me know once you guys have downloaded the file, I like to
>>> remove
>>> it from my el-cheapo hosting account ASAP.
>>> 
>>> thanks,
>>> 
>>> Rob
>>> 
>>> 
>>> On Mon, Jan 10, 2011 at 2:54 PM, Eric Carlson <eric.carlson at apple.com
>>>> wrote:
>>> 
>>>> 
>>>> On Jan 9, 2011, at 11:14 AM, Rob Coenen wrote:
>>>> 
>>>> I have written a simple test using a H264 video with burned-in timecode
>>>> (every frame is visually marked with the actual SMPTE timecode)
>>>> Webkit is unable to seek to the correct timecode using 'currentTime',
>>> it's
>>>> always a whole bunch of frames off from the requested position. I reckon
>>> it
>>>> simply seeks to the nearest keyframe?
>>>> 
>>>>  WebKit's HTMLMediaElement implementation uses different media engines
>>> on
>>>> different platforms (eg. QuickTime, QTKit, GStreamer, etc). Each media
>>>> engine has somewhat different playback characteristics so it is
>>> impossible
>>>> to say what you are experiencing without more information. Please file a
>>> bug
>>>> report at https://bugs.webkit.org/ with your test page and video file,
>>> and
>>>> someone will look into it.
>>>> 
>>>> eric
>>>> 
>>>> 
>>> 
>> 
>> 

David Singer
Multimedia and Software Standards, Apple Inc.
Received on Tuesday, 11 January 2011 14:35:41 UTC

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