The decode projects are made up of a series of decoders and tools which form a processing tool-chain for processing, analysing decoded RF samples. In order for each tool in the chain to communicate efficiently this is facilitated by a JSON metadata file is used to store and communicate information about the decoded RF capture and any data that has been determined.
Tools should (as appropriate) be able to accept metadata as well as output metadata.
This document describes the metadata format to be used by all tools in the decode tool-chain.
Supported JSON data types Name Qt Equivalent Description String QString String of UTF-8 characters Number qint32 or double Integer or real number JSON object Object Object Array Vector Vector of another type Boolean Qbool Boolean value of true or falseWhen producing a JSON metadata file the application/utility will use its normal file extension with .json added. For example, ld-decode & cvbs-decode produces a .tbc file containing the composite signal, and a .tbc.json file containing the metadata. (For colour-under formats, vhs-decode additionally produces a file with the suffix _chroma.tbc containing the chroma signal; this can be processed using the same .tbc.json metadata.)
All metadata should be considered as optional. Each tool will add metadata as appropriate but should be able to handle the case when metadata is not available.
A field with a null or -1 value (for integers) should be considered as invalid.
VBI frame numbers, sequential field numbers and field-lines are numbered starting from 1. A value of 0 should be considered as invalid.
Name Type videoParameters Object videoParameters pcmAudioParameters Object pcmAudioParameters fields Array field Name Type Description numberOfSequentialFields Integer The total number of fields decoded system String The video system in use:"PAL", "NTSC", "PAL-M" colourBurstStart Integer Position (in pixels) of the colour-burst start colourBurstEnd Integer Position (in pixels) of the colour-burst end blackLevelStart Integer Position (in pixels) of the black-level start blackLevelEnd Integer Position (in pixels) of the black-level end activeVideoStart Integer Position (in pixels) of the start of the active video line activeVideoEnd Integer Position (in pixels) of the end of the active video line white16bIre Integer The white level IRE in a 16-bit scale black16bIre Integer The black level IRE in a 16-bit scale fieldWidth Integer The width of each field in pixels fieldHeight Integer The height of each field in field-lines sampleRate Double The sample rate in Hz (usually 4 * fSC for ld-decode) tapeFormat String The type of tape media format i.g VHS, Betamax, Video8 isMapped Boolean true if the video has been mapped by ld-discmap isSubcarrierLocked Boolean true if samples are subcarrier-locked isWidescreen Boolean true if the video is 16:9 anamorphic, rather than 4:3 gitBranch String The git branch ID of ld-decode used to decode the TBC gitCommit String The git commit ID of ld-decode used to decode the TBC
A video system is a combination of a line standard and a colour standard - see TV Systems. "PAL" is standard 625-line PAL, and "NTSC" is standard 525-line NTSC; these are the only two systems used on LaserDisc. "PAL-M" is the 525-line PAL system used in Brazil, and is supported by vhs-decode. Other systems may be supported in the future.
The 'blackLevelStart' and 'blackLevelEnd' parameters point to a recommended section of the scan-line from which the average black level IRE can be determined. This is typically from the end of the colour-burst (with some safety margin) to the beginning of the active video (again with some safety margin).
fieldHeight represents the taller of the two video fields. In the .tbc file, the shorter field will be padded with an additional line at the end to make both fields the same size. The first field is always the taller of the two - that is, in 625-line systems, the whole of line 313 is considered to be part of the first field, not the second (which is not always the convention used elsewhere).
isSubcarrierLocked indicates, for video sampling rates where there are not an integer number of samples in each line of video, whether the samples are aligned to the start of lines (line-locked) or to the colour subcarrier (subcarrier-locked). For subcarrier-locked sampling, any additional samples at the end of the frame can be found at the start of the second field's padding line. PAL digital video is often subcarrier-locked with a sample rate of 4fSC, giving four extra samples after the end of the second field; for NTSC, there are an integer number of 4fSC samples in a line so it doesn't make a difference.
The VITS object contains data obtained by analysing the VITS field lines. Not all data is available in all fields (i.e. white* on NTSC)
Default:
Name Type Description wSNR real number The Signal to Noise ratio of a white (100IRE) area of the field bPSNR real number Black line PSNR (not conventional SNR)Additional fields With --verboseVITS:
Name Type Description whiteIRE real number The IRE level of the white sample, compared to the standard whiteRFLevel real number The RF level of the white sample greyPSNR real number The Peak Signal to Noise ratio of a grey (50IRE) area of the field greyIRE real number The IRE level of the grey sample, compared to the standard greyRFLevel real number NTSC ONLY: The RF level of the grey sample blackLinePreTBCIRE real number Black line IRE, before TBC/wow-flutter correction blackLinePostTBCIRE real number Black line IRE, after TBC/wow-flutter correction blackLineRFLevel real number The RF level of the black line sample syncLevelPSNR real number Sync sample PSNR (not conventional SNR) syncRFLevel real number The RF level of the sync sample syncToBlackRFRatio real number Ratio between sync and black RF signal level syncToWhiteRFRatio real number Ratio between sync and white RF signal level blackToWhiteRFRatio real number Ratio between black and white RF signal level ntscWhiteFlagSNR real number The Signal to Noise ratio of the white flag, if it exists in this field ntscWhiteFlagRFLevel real number The RF level of the white flag, if it exists in this field ntscLine19Burst0IRE real number NTSC Line 19 Color burst level after TBC/scaling ntscLine19Burst70IRE real number NTSC Line 19 70IRE burst level ntscLine19ColorPhase real number The field X color phase ntscLine19ColorRawSNR real number The field X raw SNR. This is unfiltered and should be lower than any post-processing chroma SNR, since it is ~3.59Mhz and on-disk chroma is never above 2Mhz. ntscLine19Color3DPhase real number The "3D comb filtered" color phase (second field only) ntscLine19Color3DRawSNR real number The "3D comb filtered" raw SNR (second field only). This is higher than the per-field values, but still should be below real-world chroma SNR. palVITSBurst50Level real number PAL VITS 50IRE color burst level cavFrameNr Integer CAV Frame # in VITS (useful for determining pulldown) clvMinutes Integer CLV Minute # from VITS clvSeconds Integer CLV Seconds # from VITS (not on early disks) clvFrameNr Integer Computed CLV Frame # from VITS (if clvSeconds is present)Note
This object is preliminary, and is subject to change as features are implemented within the decoders or vbi-processing tool or newer tools.
Note
See IEC 60857-1986 and IEC 60856-1986 for details.
Note
See IEC 60857-1986 Amendment 2 and IEC 60856-1986 Amendment 2 for details.
Name Type Description vbiData Integer Array The field line 16, 17 and 18 raw VBI data (as 3 elements) vp Array Array containing the VBI parameters (see belowNote
For ld-decode rev6 'vp' is removed and only vbiData is contained in the JSON.
The vp array contains the following values:
Element Type Description 0 Enum discTypes (integer) The disc type (CAV or CLV) 1 String The reported user-code for the field 2 Integer The picture number 3 Integer The chapter number 4 Number (integer) CLV programme time code hours 5 Number (integer) CLV programme time code seconds 6 Number (integer) CLV Current seconds value 7 Number (integer) CLV Current frame number (1-25 for PAL, 1-30 for NTSC) 8 Enum – Programme status - soundModes (integer) Current sound mode 9 Enum – soundModes (integer) Am2 Current sound mode 10 Integer 12-bit word of boolean flags (see below)Flags (bit 0 is LSB):
bit Name Description 0 leadIn true = field is lead-in 1 leadOut true = field is lead-out 2 picStop true = field has stop-code set 3 cx Programme status - true = CX is on 4 size Programme status - true = disc is 12", false = disc is 8" 5 side Programme status - true = side 1, false = side 2 6 teletext Programme status - true = teletext data is present on the disc 7 dump Programme status - true = programme dump - See IEC specification 8 fm Programme status - true = FM-FM Multiplex - See IEC specification 9 digital Programme status - true = Video contents are digital - See IEC specification 10 parity Programme status - true = parity confirmed as correct, false = parity not confirmed 11 copyAm2 true = copying is allowed - See IEC Am2 specification 12 standardAm2 Am2 true = video signal is standard, false = future useNote: This object contains the field data that is specific to NTSC (and not present in the PAL IEC specifications)
Name Type Description isFmCodeDataValid Boolean true = FM code data is valid, false = FM code data is invalid fmCodeData Number (integer) The 20-bit FM code data payload (X5 to X1) fieldFlag Boolean true = first video field, false = not first video field whiteFlag Boolean true = white flag, false = white flag not present isVideoIdDataValid Boolean true = VIDEO ID data is valid, false = VIDEO ID data is invalid videoIdData Number (integer) The 14-bit VIDEO ID code data payload (IEC 61880)This object represents Closed Caption data for a field.
Name Type Description ccData0 Number (integer) The first closed caption byte ccData1 Number (integer) The second closed caption byteFor ccData0 and ccData1, if the value is -1 or not present then no valid CC was found. 0 is a valid value - it means that CC is present, but no data is being transferred on this line.
Note: See ANSI/CTA-608 for details.
This object represents Vertical Interval Timecode data for a field.
Name Type Description vitcData Integer Array VITC raw data as 8 valuesEach of the values in vitcData represents 8 bits of the raw VITC data, without the framing bits or CRC. The LSB of vitcData[0] is VITC bit 2 (the LSB of the frame number), and the MSB of vitcData[7] is VITC bit 79.
This describes types of LaserDisc.
discTypes number (32-bit integer)
Name Value unknownDiscType 0 clv 1 cav 2soundModes number (32-bit integer)
Note
See IEC 60857-1986 and IEC 60856-1986 for details.
Name Value stereo 0 mono 1 audioSubCarriersOff 2 bilingual 3 stereo_stereo 4 stereo_bilingual 5 crossChannelStereo 6 bilingual_bilingual 7 mono_dump 8 stereo_dump 9 bilingual_dump 10 futureUse 11RetroSearch is an open source project built by @garambo | Open a GitHub Issue
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