- From: Philip Jägenstedt <philipj@opera.com>
- Date: Thu, 21 Oct 2010 10:31:03 +0200
- To: public-media-fragment@w3.org
On Thu, 21 Oct 2010 01:48:53 +0200, Silvia Pfeiffer <silviapfeiffer1@gmail.com> wrote: > On Thu, Oct 21, 2010 at 10:39 AM, Silvia Pfeiffer > <silviapfeiffer1@gmail.com> wrote: >> On Thu, Oct 21, 2010 at 10:32 AM, Chris Double <cdouble@mozilla.com> >> wrote: >>> On Thu, Oct 21, 2010 at 12:24 PM, Silvia Pfeiffer >>> <silviapfeiffer1@gmail.com> wrote: >>>>> How do you convert SMPTE to ms when you don't know the framerate? >>>>> WebM >>>>> doesn't provide that information. >>>> >>>> How do you know at what speed to display WebM files if you don't have >>>> a framerate? I'm confused... >>> >>> We use the timestamps on the frame to know when that frame needs to be >>> displayed. >> >> Oh, so it's possible to have a non-fixed framerate in WebM? Hmm... >> Silvia. >> > > It seems to me, looking at > http://groups.google.com/a/webmproject.org/group/webm-discuss/browse_thread/thread/2f0120b464b536c1/e7e1003f1be4c4fa?lnk=st&q=smpte#e7e1003f1be4c4fa > , one could use the TimecodeScale to calculate the conversion. Since > SMPTE is just a marker, it doesn't actually matter what frame rate the > video is encoded in. You can convert the SMPTE time marker to an > actual ms time and back only depending on what frame rate SMPTE you > pick. The actual frames available don't matter since SMPTE on digital > files isn't actually properly counting frames. This is why I call it a > marker and not a counter. WebM files don't have to know their own framerate, and if it does it is only informational and not actually used for playback. However, the SMPTE formats actually assume a framerate, taking a guess: smpte: 30000/1001? smpte-25: 25? (if so, could be represented with 3 decimal points) smpte-30: 30? smpte-30-drop: 29.97? See http://en.wikipedia.org/wiki/SMPTE_time_code#Drop_frame_timecode What does one do when the framerate assumed by the format doesn't match the resource, or the framerate of the resource isn't known? -- Philip Jägenstedt Core Developer Opera Software
Received on Thursday, 21 October 2010 08:31:43 UTC