VirtualBox recorded session timings

[Mike Newell]

I've been using the VirtualBox "record" option to record some training
stuff, however the results have an issue: in the PV8 video stream the
stream start time is given as a huge number (usually several hours).
For example one recent stream I recorded was 1.5 hours long, but since
the start time was at about 2.75 hours the resulting stream appeared to
be 4.15 hours long when played back on VLC. This leads to two problems:

1. Syncing the separately recorded audio is harder because you have to
factor in whatever the video start time is, and
2. When playing back with an application that cares (like VLC) the
video appears to be very long. If you use the slide bar to move
ahead in the video you have to be careful not to move past the
actual video length or you get blank video.

This can be fixed by re-encoding, but that has its own set of issues
(and takes forever).

Is there any way to fix VB so it marks recording start at 0 time? Where
DOES VB get its start time from? It's not from when the guest is booted
- I only had the guest up a few minutes before starting the recording
and VB marked the start as noted above.

Thanks!

Mike

[Frank Mehnert]

Mike,

Post by Mike Newell
I've been using the VirtualBox "record" option to record some training
stuff, however the results have an issue: in the PV8 video stream the
stream start time is given as a huge number (usually several hours).
For example one recent stream I recorded was 1.5 hours long, but since
the start time was at about 2.75 hours the resulting stream appeared to
1. Syncing the separately recorded audio is harder because you have to
factor in whatever the video start time is, and
2. When playing back with an application that cares (like VLC) the
video appears to be very long. If you use the slide bar to move
ahead in the video you have to be careful not to move past the
actual video length or you get blank video.
This can be fixed by re-encoding, but that has its own set of issues
(and takes forever).
Is there any way to fix VB so it marks recording start at 0 time? Where
DOES VB get its start time from? It's not from when the guest is booted
- I only had the guest up a few minutes before starting the recording
and VB marked the start as noted above.

not sure if we are talking about the same problem but the time stamp
of video-recordings start when video capturing starts. That is, if you
start your VM, then do something and 2 hours later you decide to start
capturing then the video time stamp will start at 2 hours. If you pause
the video capture and continue it later then the time stamps will jump.
The time stamp of the video is always synchron with the VM runtime. I
don't consider this a bug but as a feature.

If you think this does not fit your needs and the time stamp should
always start at 0 and should only advance if recording is active (i.e.
don't jump if capturing is paused) then this can be certainly implemented.

Kind regards,

Frank
--
Dr.-Ing. Frank Mehnert | Software Development Director, VirtualBox
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[Mike Newell]

Post by Frank Mehnert
not sure if we are talking about the same problem but the time stamp
of video-recordings start when video capturing starts. That is, if you
start your VM, then do something and 2 hours later you decide to start
capturing then the video time stamp will start at 2 hours. If you
pause the video capture and continue it later then the time stamps
will jump. The time stamp of the video is always synchron with the VM
runtime. I don't consider this a bug but as a feature. If you think
this does not fit your needs and the time stamp should always start at
0 and should only advance if recording is active (i.e. don't jump if
capturing is paused) then this can be certainly implemented. Kind
regards, Frank

Thanks for the rapid reply! I guess I wasn't clear in the original
message... I started a VM (Windows 7 guest) and once it was up started
the recording. I recorded for about an hour and a half. The resulting
WebM stream had a start time stamp of just shy of three hours and an
apparent length of just over 4 hours (according to VLC). I don't
believe the VM was running for 2+ hours before I started recording, but
it's possible. Having a non-zero start time is confusing because it's
harder to line up audio tracks and also players like VLC think the video
is much longer than it is so the slide bar doesn't work like you'd think
it would (e.g. if you slide the bar to advance to what appears to be the
middle of the video you've actually gone way past the end).

That said it would be MUCH better if the video timestamp were to start
at 0 (without having to recode the video :-). Is there a setting
somewhere that can force VirtualBox recordings to start at 0? I looked
but didn't find anything on the InterWebs about it.

Thanks!

Mike