[Q] Conversion of SCC file containing Field 2 (CC3/4), including PAC codes

Firstly, many thanks to Rob & Co for sharing caption-inspector with the open source community. I've been using caption-inspector for a few years for field 1 data.

However, recently I have been attempting to decode SCC files containing field 2 (CC3/4) data with caption-inspector.

### Test Case - Field 1(CC1/2) only

Below is a test case containing.
CC1: AAAAAAAA
CC2: aaaaaaaa

```
Scenarist_SCC V1.0

00:00:00;00 9420 94ae 9140 c1c1 c1c1 c1c1 c1c1 942f 1c20 1cae 1940 6161 6161 6161 6161 1c2f
```

✅ This successfully decodes to CC1/2 as expected.

```
Decoded Line 21 / CEA-608 for Asset: ./captioninspector/field1-C1 - Channel: 1
00:00:00:00 - {RCL} {ENM} {R1:White} "AAAAAAAA"
00:00:00:07 - {EOC}

Decoded Line 21 / CEA-608 for Asset: ./captioninspector/field1-C2 - Channel: 2
00:00:00:08 - {RCL} {ENM} {R1:White} "aaaaaaaa"
00:00:00:15 - {EOC}
```

### Test Case - Field 2(CC3/4) only, containing PAC codes

If I take a field 2 CC3/4 equivalent test case containing:
CC3: XXXXXXXX
CC4: xxxxxxxx

```
Scenarist_SCC V1.0

00:00:00;00 1520 15ae 9140 5858 5858 5858 5858 152f 9d20 9dae 1940 f8f8 f8f8 f8f8 f8f8 9d2f
```

❌ The field 2 SCC file does not decode as expected. The PAC codes `{R1:White}` `9140` and `1940` are interpreted as always belonging to field 1, and instead of producing a decode containing CC3/4, caption-inspector extracts the PAC and payload as if they belong in field 1/CC1&2.

```
Decoded Line 21 / CEA-608 for Asset: ./captioninspector/field2-C1 - Channel: 1 {R1:White} "XXXXXXXX

Decoded Line 21 / CEA-608 for Asset: ./captioninspector/field2-C2 - Channel: 2 {R1:White} "xxxxxxxx

Decoded Line 21 / CEA-608 for Asset: ./captioninspector/field2-C3 - Channel: 3
00:00:00:00 - {RCL} {ENM}
00:00:00:07 - {EOC}

Decoded Line 21 / CEA-608 for Asset: ./captioninspector/field2-C4 - Channel: 4
00:00:00:08 - {RCL} {ENM}
00:00:00:15 - {EOC}
```

I believe that PAC codes `{R1:White}` `9140` and `1940` codes are correct, even when used in Field 2. I have cross referenced against [McPoodle's 7 bit parity tables](http://www.theneitherworld.com/mcpoodle/SCC_TOOLS/DOCS/CC_CODES.HTML), which although is not anything near a reference implementation of SCC/608, but is at least an independent 3rd party interpretation of CTA-608 / Title 47.

✅ Removing the PAC codes from a field 2 SCC file results in an expected decode on channels 3 & 4

```
Scenarist_SCC V1.0

00:00:00;00 1520 15ae 5858 5858 5858 5858 152f 9d20 9dae f8f8 f8f8 f8f8 f8f8 9d2f
```
```
Decoded Line 21 / CEA-608 for Asset: ./captioninspector/field2-without-pac-C3 - Channel: 3
00:00:00:00 - {RCL} {ENM} "XXXXXXXX"
00:00:00:06 - {EOC}

Decoded Line 21 / CEA-608 for Asset: ./captioninspector/field2-without-pac-C4 - Channel: 4
00:00:00:07 - {RCL} {ENM} "xxxxxxxx"
00:00:00:13 - {EOC}
```

Although it is noted that even this final example without PAC codes, caption-inspector reports `Channel/Field Mismatch` on an SCC file containing Field 2 data.

``` bash
$ grep -i 'ERROR' "./captioninspector/field2-without-pac.dbg"
ERROR DBG_608_DEC [line21_decode.c:441] - Channel/Field Mismatch: Chan - 3 Field - 0
ERROR DBG_CCD_OUT [cc_data_output.c:396] - Channel/Field Mismatch: Chan - 3 Field - 1 Code - RCL
ERROR DBG_608_DEC [line21_decode.c:441] - Channel/Field Mismatch: Chan - 3 Field - 0
ERROR DBG_CCD_OUT [cc_data_output.c:396] - Channel/Field Mismatch: Chan - 3 Field - 1 Code - ENM
ERROR DBG_608_DEC [line21_decode.c:441] - Channel/Field Mismatch: Chan - 3 Field - 0
ERROR DBG_CCD_OUT [cc_data_output.c:396] - Channel/Field Mismatch: Chan - 3 Field - 1 Code - EOC
ERROR DBG_608_DEC [line21_decode.c:441] - Channel/Field Mismatch: Chan - 4 Field - 0
ERROR DBG_CCD_OUT [cc_data_output.c:396] - Channel/Field Mismatch: Chan - 4 Field - 1 Code - RCL
ERROR DBG_608_DEC [line21_decode.c:441] - Channel/Field Mismatch: Chan - 4 Field - 0
ERROR DBG_CCD_OUT [cc_data_output.c:396] - Channel/Field Mismatch: Chan - 4 Field - 1 Code - ENM
ERROR DBG_608_DEC [line21_decode.c:441] - Channel/Field Mismatch: Chan - 4 Field - 0
ERROR DBG_CCD_OUT [cc_data_output.c:396] - Channel/Field Mismatch: Chan - 4 Field - 1 Code - EOC
```

_Question: Does caption-inspector support field 2(CC3/4) input from SCC/SC2 files or does it assume that all SCC files (and PAC codes therein) are field 1?_ Or have I misinterpreted how field 2(CC3/4) should be included within an SCC/SC2 file. Thanks!