writing MXF video the includes GPS times

[Cory Albright]

I am needing to export rendered frames from my application to an MXF
video file.  The application is rendering based on a GPS time-clock and
I need to have the GPS time embedded into the frame headers of the MXF
video.   Does the MXF plugin for gstreamer support this?

Thank you for your time,

- Cory


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[Sebastian Dröge-7]

On Wed, 2011-08-10 at 17:30 -0600, Cory Albright wrote:
> I am needing to export rendered frames from my application to an MXF
> video file.  The application is rendering based on a GPS time-clock and
> I need to have the GPS time embedded into the frame headers of the MXF
> video.   Does the MXF plugin for gstreamer support this?

Hi,
currently the MXF plugin does not support this but it should be possible
to add support for this. Based on which specification do you want to add
the GPS time into the frame headers?

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[Josh Doe]

2011/8/11 Sebastian Dröge <[hidden email]>

On Wed, 2011-08-10 at 17:30 -0600, Cory Albright wrote:
> I am needing to export rendered frames from my application to an MXF
> video file.  The application is rendering based on a GPS time-clock and
> I need to have the GPS time embedded into the frame headers of the MXF
> video.   Does the MXF plugin for gstreamer support this?

Hi,
currently the MXF plugin does not support this but it should be possible
to add support for this. Based on which specification do you want to add
the GPS time into the frame headers?

I would be interested in this as well, as I'll likely have a need to support this in the future. Do you want to save the GPS (UTC) date and time along with every frame (perhaps interpolated), just at the start (using relative offsets for each frame), or at the sampling rate of the GPS (typ. 1-10Hz)?

Taking a quick look at the SMPTE metadata dictionary shows a lot of time-related keys, but I haven't worked with this before so I'm not sure which ones are appropriate. The SMPTE item for temporal keys is 07.02.00.00.00.00.00.00. My complete guess without reading any of the standards or RPs would be that you'd want to use: 07.02.01.02.01.01.00.00: Material Start True Date-Time, UTC, ("Absolute time at start of creating the segment, shot, clip, item etc."). Again, a complete guess, I'm not sure what's recommended or actually supported by software implementations.

-Josh

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[Cory Albright]

Unfortunately I do not have a specification for exactly how the GPS time is embedded, but I do have a sample video that was constructed by different means that does contain the GPS times.  Maybe a little reverse engineering will help with this.  I am new to gstreamer (and MXF), so I still have some learning to do.
     It is my understanding that the time is to be saved in the header of each frame, as opposed to a timestamp at the start and calculating relative offsets based on frame number.

- Cory



2011/8/11 Sebastian Dr?ge<[hidden email]>

> On Wed, 2011-08-10 at 17:30 -0600, Cory Albright wrote:
>> I am needing to export rendered frames from my application to an MXF
>> video file.  The application is rendering based on a GPS time-clock and
>> I need to have the GPS time embedded into the frame headers of the MXF
>> video.   Does the MXF plugin for gstreamer support this?
> Hi,
> currently the MXF plugin does not support this but it should be possible
> to add support for this. Based on which specification do you want to add
> the GPS time into the frame headers?
>

I would be interested in this as well, as I'll likely have a need to support

this in the future. Do you want to save the GPS (UTC) date and time along
with every frame (perhaps interpolated), just at the start (using relative
offsets for each frame), or at the sampling rate of the GPS (typ. 1-10Hz)?

Taking a quick look at the SMPTE metadata dictionary shows a lot of
time-related keys, but I haven't worked with this before so I'm not sure
which ones are appropriate. The SMPTE item for temporal keys is
07.02.00.00.00.00.00.00. My complete guess without reading any of the
standards or RPs would be that you'd want to use: 07.02.01.02.01.01.00.00:
Material Start True Date-Time, UTC, ("Absolute time at start of creating the
segment, shot, clip, item etc."). Again, a complete guess, I'm not sure
what's recommended or actually supported by software implementations.

-Josh



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[Sebastian Dröge-7]

On Thu, 2011-08-11 at 10:16 -0600, Cory Albright wrote:
> Unfortunately I do not have a specification for exactly how the
> GPS time is embedded, but I do have a sample video that was
> constructed by different means that does contain the GPS times.
> Maybe a little reverse engineering will help with this.  I am
> new to gstreamer (and MXF), so I still have some learning to do.
>      It is my understanding that the time is to be saved in the
> header of each frame, as opposed to a timestamp at the start and
> calculating relative offsets based on frame number.

You should really get the MXF specs from SMPTE then. Currently it works
the way how you described it but it's possible to have timecode tracks
and then timecode information in the System element of every edit unit.
There are multiple standards for storing the timecode information.

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