ancillary time code (atc) according to smpte 12m-2
DESCRIPTION
Several methods have been defined to allow time code to be embedded in video. SMPTE 12M-2 is applies to Analog and standard definition video. Other standards apply for HD.TRANSCRIPT
5/9/13 Alpermann+Velte time code and ancillary data systems, faq, Ancillary Time Code (ATC) according to SMPTE 12M-2
www.alpermann-velte.com/faq_e/e_atc.html 1/2
Ancillary Time Code (ATC) according to SMPTE 12M2
Overview
The SMPTE standard SMPTE 12M22008 defines the “Transmission of Time Code in the Ancillary Data Space” and replaces the RP188. In the past there were different methods of implementations regarding ATC. This note describes the implementation of ATCaccording to SMPTE 12M2 and what are the changes regarding Alpermann+Velte time code modules.
The following specifications are concerned with ancillary time code:
Standard DID DBN/SDID DC Time CodeType Remark
RP 196 64h64h
64h7Fh
8h9h
HANC LTCHANC VITC
No longer listed!
SMPTE 291M F5h 00h 8h LTC Specification unknown!
RP 188/SMPTE 12M2 60h 60h 10h ATC RP 188 led to different im
plementations!
It is strongly recommended to implement ATC according to SMPTE 12M2!
Introduction
There are four transport methods of time code known (regarding only “12M” time codes, so not dealing with MPEG, film, digital audio, midietc.):
LTC Transported as a serial (analogue audio) signal independent of any video signal.
VITC Inserted in an active line within the VBI of an analogue video signal.
DVITC Similar to the VITC inserted in an active line within the VBI of a digital video signal.
ATC Ancillary data packets carried in the ancillary data space of a digital data stream.
Remarks regarding the DVITC: There is no specification of DVITC for HD digital video! ATC can be used for SD digital video as well.
For HD digital video ATC should be used.
ATC can be of type ATC_LTC and ATC_VITC.
The ancillary data spaces of a digital television data streamare HANC in the horizontal blanking area and VANC inthe vertical blanking interval.
HANC:All lines after EAV but before SAV.
VANC: In the vertical blanking region after SAV but beforeEAV.
Ancillary data packets should not be located in the lines identified as a switch point – defined by SMPTE RP 168.
Format of Ancillary Time Code Packets
SMPTE 291M defines the format for a type 2 ANC packet.
16 User Data Words consist of time code data and the type of time code, i.e. LTC or VITC or further user defined time codes.For HD digital video the ANC packets shall be carried in the Y stream.ATC according to SMPTE 12M2 is applicable to 8, 10, or 12bit television systems.
5/9/13 Alpermann+Velte time code and ancillary data systems, faq, Ancillary Time Code (ATC) according to SMPTE 12M-2
www.alpermann-velte.com/faq_e/e_atc.html 2/2
Recommendations of SMPTE 12M2
Location for ATC in HD video: ATC_VITC in HANC, line 9,ATC_LTC in HANC, line 10.
Location for ATC in SD video: in VANC as early as possible from line 9 of 625/50/I and line 13 of 525/59.94/I.
Counting frames up to 50 or 60 is not provided, so for progressive systems running at greater than 30 framespersecond each time codecount references a frame pair. The first frame of the frame pair receives the new time address which then will be repeated at the secondframe. With LTC it is not possible to distinguish between the frames of a pair, but the VITC marks the individual frames using the fieldflag. Evaluating this flag enables a time code reader or inserter to identify the first or second frame.
Interlaced:
Progr. 25/30 frames:
Progr. 50/60 frames:
Something New and Special
ATC_VITC: In detail the ATC_VITC consists of two types, VITC1 and VITC2. Apart from this type definition the payload of both types is identical.Implementations of VITC1 and VITC2 should be used to distinguish between the fields of interlaced formats and the frames of a framepair of progressive formats, together with the field mark flag. Now only ATC_VITC will be presented, and the internal encoder or decoderhandles the VITC1 and VITC2 type.
Older versions of the RUBIDIUM modules DT/DV and HT/HV as well as our PC boards PCIHD, PCIeD and PCIeHD have treated VITC1and VITC2 as separate time codes, this now has changed:
DT/DV and HT/HV from version 2.0.168, November 2009,
PCIHD/PCIeD/PCIeHD from version 7.19, October 2009.
After an update please take care using only the latest configuration tools and drivers.
ATC_LTC: The SMPTE 12M2 gives not a clear recommendation about the transmission rate of the ATC_LTC: „... at least once a frame ...“. Ininterlaced video formats the transmission rate may be once a frame or every field. We decided to offer the onceaframe method as adefault, inserting the ATC_LTC in the first field. The user may select the everyfield method by activating the „All Fields“ checkbox. Thisconcerns our RUBIDIUM modules DT/DV and HT/HV.
ATC_LTC > ATC_VITC: The HT and HV modules are our time code converters in HD digital video systems. If only ATC_LTC is present in a progressive videosystem with frame rate greater than 30 frames per second or in interlaced systems, these converter modules are able to convert theATC_LTC to an ATC_VITC. This method will keep the time addresses and add the advantage of the field flags, thus making the individualframes/fields distinguishable.
Others: You can download the latest versions from: Software
Please don’t hesitate to contact Alpermann+Velte if you have any ATC problems. We would like to help analyzing this problem.
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