- From: David Singer <singer@apple.com>
- Date: Tue, 11 Jan 2011 23:51:22 +0100
OK, but it does seem kinda a tautology if you say "I want to use a time-expression that represents fractions of seconds as frame numbers, and it's not very accurate if there aren't very many frames/second..." ! On Jan 11, 2011, at 23:40 , Rob Coenen wrote: > Hi David- that is b/c in an ideal world I'd want to seek to a time expressed as a SMPTE timecode (think web apps that let users step x frames back, seek y frames forward etc.). In order to convert SMPTE to the floating point value for video.seekTime I need to know the frame rate. > > -Rob > > On Tue, Jan 11, 2011 at 10:35 PM, David Singer <singer at apple.com> wrote: > 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. > > David Singer Multimedia and Software Standards, Apple Inc.
Received on Tuesday, 11 January 2011 14:51:22 UTC