Re: [time-nuts] Timestamps in audio files?

[Magnus Danielson]

Jim,

On 12/21/2015 04:22 PM, Jim Lux 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.


The time-code (SMPTE 12M), often referred to as LTC or VITC, often 
accompany the media. However, it's a relative timing and really not an 
absolute timing. This means that initial delays and processing delays is 
not being captured. Lip-sync is being monitored and re-established using 
delays. Lip-sync is easily lost these days, as apparent regularly.


With the SMPTE 2059-1 and 2059-2, such time may have an improved 
connection to normal wall-time, but still no real handling of delays.


Cheers,
Magnus
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Re: [time-nuts] Timestamps in audio files?

[Götz Romahn]

there is a timecode associated with Audio CDs.
https://en.wikipedia.org/wiki/Compact_Disc_Digital_Audio
maybe this helps, Götz


Am 21.12.2015 um 22:06 schrieb Hal Murray:


tsho...@gmail.com said:

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.


What sort of accuracy to you want?  Is nearest second good enough or do you
want time-nut level accuracy?

One thing to keep in mind is that the recording clock may not be accurate, so
if all you know is the start time, your error bars grow as you move down the
file.

Recording IRIG on another channel is the best suggestion I've seen.




--
Götz Romahn
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Re: [time-nuts] Timestamps in audio files?

[Chris Caudle]

On Mon, December 21, 2015 5:19 am, Tim Shoppa wrote:
> Are there any standard consumer-type audio file formats, that support
> absolute time time/datestamps?

Broadcast WAV file (BWF) is probably the closest.  I'm not sure what
different timecode formats are possible, but this description of how Avid
and Final Cut import time code from BWF files probably indicates what is
commonly used.  I think the usual timecode roles over every 24 hours, I'm
not sure there is a standard way to attach calendar date.  Could be a way
that just isn't decribed here:

BWF Time Code
The recorded files generated by Sound Devices 7-Series recorders and the
552 mixer contain extensive metadata describing their contents. This
metadata is stored in the BeXT and iXML chunks within the Broadcast Wave
format. To represent time code the primary metadata parameters include:

Start TC:  stored in both the bEXT and iXML chunks as a ‘Samples Since
Midnight’ value.
TC frame rate:  This is the frames per second rate. It is also used to
convert the HH:MM:SS:FF time code value to a ‘Samples Since Midnight’
value and visa versa. It is stored in the bEXT chunk as the ‘SPEED’
parameter and in iXML as the ‘TIMECODE_RATE’ parameter.
Sampling Rate:  This is stored in the ‘fmt’ (format) and iXML chunks.
This tells the playback device at what speed to playback the file,
typically 48 kHz in sound-for-picture applications.

-- 
Chris Caudle




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Re: [time-nuts] Timestamps in audio files?

[Tim Shoppa]

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  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  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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> > and follow the instructions there.
>
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Re: [time-nuts] Timestamps in audio files?

[Hal Murray]

tsho...@gmail.com said:
> 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. 

What sort of accuracy to you want?  Is nearest second good enough or do you 
want time-nut level accuracy?

One thing to keep in mind is that the recording clock may not be accurate, so 
if all you know is the start time, your error bars grow as you move down the 
file.

Recording IRIG on another channel is the best suggestion I've seen.


-- 
These are my opinions.  I hate spam.



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Re: [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  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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> To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
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Re: [time-nuts] Timestamps in audio files?

[Jim Lux]

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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