Analogies to broadcast timing are interesting, but that seems like a non-starter today due to multiple cascaded codec latencies.
The video formats I know that use timestamps for historical reconstruction, just recorded a human-readable timestamp onto the video itself at original recording time. Jim, I agree that playing games with the timestamp cause problems with many players that expect the start to be "00:00:00". Certainly embedding time info into the transport layer is a possibility. I'm more interested in the "file" layer today. I remember to the last time I had to extensively work with analog recordings with IRIG-type timestamps. The playback console had a LED playback-clock readout and it was very impressive because with variable-speed analog playback the LED readout's IRIG decoder would maintain lock to the timecode. (It must've been one of the amplitude-modulated IRIG codes now that I think about it, because it would show hundredths of a second - IRIG-B? - and sometimes we would record it on a polaroid with a scope and count off fractions of 0.01s. Or maybe it was 0.001s.) Tim N3QE On Mon, Dec 21, 2015 at 12:40 PM, Bob Camp <kb...@n1k.org> wrote: > Hi > > I sort of suspect that if there *was* a system “broadcasting” time over > the internet > (other than NTP) we all would be fooling around locking up oscillators to > it … > > Yes, streaming and time stamping are not the same thing. These days > though, the > two probably get crossed between a lot. > > Bob > > > On Dec 21, 2015, at 10:22 AM, Jim Lux <jim...@earthlink.net> wrote: > > > > On 12/21/15 3:19 AM, Tim Shoppa wrote: > >> As an adjunct to the thread about timestamped samples of LORAN > >> transmissions... > >> > >> Are there any standard consumer-type audio file formats, that support > >> absolute time time/datestamps? Would not have to be done continuously, > but > >> something like a time and date stamp inserted nearest each sample on a > >> second boundary. > >> > >> I have worked with some analog tape audio formats in the past where > >> IRIG-type timestamps were written on a separate channel or on a > subcarrier. > >> > >> I know of many proprietary digital recording applications that make > WAV's > >> or MP3's or proprietary codec formats, where the filename includes a > >> timestamp. Much more interested in standard formats where the timestamp > is > >> embedded in the file itself. > >> > > > > For RF recordings, VITA49 has a standard for timestamps in the packet > headers (4 flavors of epoch, multiple flavors of time format and precision) > > > > Video file formats seem to draw from older time code things like SMPTE > and are "relative" (so you're always fooling around trying to figure out > the offsets). I spent a few days earlier this year trying to put absolute > time subtitles on video files using all manner of tools, and it was > frustrating (ffmpeg, vlc, etc.. all were to no avail). Trying to put UTC > time into embedded timecode was also pretty unproductive (most tools don't > like to see the first frame occurring at a time very different from > 00:00:00:00) > > > > > > In fact, in the music file world (e.g. MIDI) you see references to > absolute and relative time, and there, they are really talking about time > measured in seconds vs time measured in beats; e.g. whether the duration of > something is 1 second, or 2 quarter notes, which might be the same if the > tempo is 120bpm. > > > > > > You might look for solutions for people trying to synchronize multiple > multimedia streams delivered over the internet (e.g. slides and > accompanying narration or music) because they actually have a need for > "show this slide at time HH:MM:SS and play this sound at HH:MM:SS" kind of > synchronization. > > > > I suspect, though, that this kind of info gets encapsulated in the > transport layer, rather than the underlying files holding the info. > > > > > > > > _______________________________________________ > > time-nuts mailing list -- time-nuts@febo.com > > To unsubscribe, go to > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > > and follow the instructions there. > > _______________________________________________ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. > _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
