[Matroska-devel] ReferenceTimecode tracks in Matroska proposal

Kieran O Leary kieran.o.leary at gmail.com
Mon Jan 11 01:34:45 CET 2016


On 10 Jan 2016 10:57 pm, "Dave Rice" <dave at dericed.com> wrote:
>
> Hi all,

Hi,

I don't have much to add except that I'm delighted to see this addressed
and it looks like a great addition to the matroska format. Some comments
further down.
>
> Here is an early draft of Elements for managing ReferenceTimecode tracks.
Matroska uses the term 'Timecode' to reference presentation timestamps,
whereas other formats (QuickTime, MXF) use 'Timecode' to reference a time
reference that is added to the timeline which is inpendent of the
presentation (i.e. a QuickTime file with a timecode track that starts at
one hour aka 1:00:00;00 would not cause a one hour delay before playback
starts). In the context of Matroska I am using ReferenceTimecode (for now)
to refer to QuickTime/MXF style timecode tracks.
>
> TrackType:
> Add to the TrackType definition to list "0x13: timecode,"
>
> CodecID:
> Add the following timecode Codec IDs.
> Codec ID        | Name               | Description
> T_QUICKTIME     | QuickTime Timecode | Timecode data as stored in
QuickTime, e.q. tmcd. The CodecPrivate contains all additional data that is
stored in the 'tcmd' (timecode) atom in the QuickTime file.
> Others? LTC? VITC?

I have mostly encountered QuickTime tmcd info thus far. I haven't
reformatted any mxfs as mkv yet, but tmcd info within matroska would be
fantastic from my perspective.
>
> Proposed elements under TrackEntry:
>
> Element Name: ReferenceTimecode
> Level:        3
> ID:           [EF]
> Mandatory:    -
> Multiple:     -
> Default:      -
> Type:         m
> Description:  ReferenceTimecode settings
>
> Element Name: ReferenceTimecodeForm
> Level:        4
> ID:           [EF][A1]
> Mandatory:    mand.
> Multiple:     -
> Range:        0-2
> Default:      0
> Type:         u
> Description:  Indicates the form of expression used to present the
timecode (using HH for hours, MM for minutes, SS for seconds, mmm for
milliseconds, ff for frames).
>               0: HH:MM:SS.mmm
>               1: HH:MM:SS:ff (non-drop frame)
>               2: HH:MM:SS;ff (drop frame)
>

I don't know if this flag is explicitly mentioned in a QuickTime
container,but it seems to me to be a great idea to flag this message info.
> Element Name: ReferenceTimecode24HourMax
> Level:        4
> ID:           [EF][A2]
> Mandatory:    mand.
> Multiple:     -
> Range:        0-1
> Default:      0
> Type:         u
> Description:  Indicates if the timecode should revert to a zero-value at
the time reference of 24 hours. Set to 1 if the ReferenceTimecode should
use a maximum value of 24 hours and wrap values back to zero hours at that
point.
>
> For storage of ReferenceTimecode values in Blocks, I suggest storing a
signed integer (ReferenceTimecode values may be negative). The stored
signed integer would be the frame number (players supporting
ReferenceTimecode should convert the frame number accordingly to a
drop-frame or non-drop-frame display). So if ReferenceTimecodeForm=1, the
Block stores 0x00BC, and the frame duration is NTSC, then the displayed
value would be 00:00:06:08. The next value 00:00:06:09, etc.
>
> I propose that one block per ReferenceTimecode not be required for simple
incrementing ReferenceTimecode, but that the ReferenceTimecode value of the
next video frame be considered to be either 1 greater than the previous
value (if ReferenceTimecodeForm is 1 or 2) or increased by the duration of
the corresponding video frame.
>
> If the ReferenceTimecode is non-continuous then a new ReferenceTimecode
value in a new Block with a new Timecode (Matroska meaning of Timecode)
could be inserted at the point of the discontinuity.
>
> Comments?
> Dave Rice

Best,

Kieran.
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