[time-nuts] Timestamps in audio files?

[Bob Camp]

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 <jimlux at 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.
> 
> 
> 
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