Unless I've misunderstood what you are explaining - the tool seems to work OK with a firmware file from the Hikvision China website.
I started with this file from the link you specified
NVR_(71-4,8路-SN)QDBL_CN_STD_V3.0.10_141128.zip
and used 'split' to extract the contents into a folder.
I made a small edit to 'start.sh' and used 'create' to re-create the firmware, using the original digicap.dav for the header.
The resultant file was the correct size (20 bytes larger, I'd added a line to start.sh), and was listed as having these contents:
HIK firmware header converter 0.4R
Head raw data(108b) :
00000000 E9 9A F7 B6 7A 94 DD D3 76 B8 A3 AB B6 CB B5 BE ....z...v.......
00000010 CF BC FE D6 E6 DD D3 BA 46 5C 54 40 34 4A 41 45 ........F\T@4JAE
00000020 43 01 29 35 22 2C 45 46 5C 54 40 34 B5 BE BA CD C.)5",EF\T@4....
00000030 FE D6 CA DD D3 BA B9 A3 AB BF CB B5 BE BA CD BC ................
00000040 BE A3 AE BA 94 CD C2 D9 91 A7 CF D3 DB CD BC FE ................
00000050 CA DD D3 BA B9 A3 AB BF CB B5 BE BA CD BC FE D6 ................
00000060 11 D2 BA B9 82 09 B3 CB CE A8 F3 CB
Head decoded data(108b) :
00000000 53 57 4B 48 AC 5E 00 00 CC 01 00 00 09 00 00 00 SWKH.^..........
00000010 02 00 00 00 2C 00 00 00 FF FF FF FF FF FF FF FF ....,...........
00000020 FF FF FF FF FF FF FF FF FF FF FF FF 00 00 00 00 ................
00000030 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
00000040 68 69 73 69 2E 74 61 72 2E 6C 7A 6D 61 00 00 00 hisi.tar.lzma...
00000050 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
00000060 CC 01 00 00 21 A2 0C 00 7B 16 49 06
Magic number : 0x484B5753
iHeaderCheckSum : 0x00005EAC [24236]
iHeadTotalLen : 0x000001CC [460]
iFileNum : 0x00000009 [9]
iLanguage : 0x00000002 [2] CN
iDeviceClass : 0x0000002C
iOEMCode : 0xFFFFFFFF
iFirmwareVer : 0xFFFFFFFF
iFeature: 0xFFFFFFFF
Calculated CheckSum : 0x00005EAC [24236]
Full decoded data (with full files block):
00000000 53 57 4B 48 AC 5E 00 00 CC 01 00 00 09 00 00 00 SWKH.^..........
00000010 02 00 00 00 2C 00 00 00 FF FF FF FF FF FF FF FF ....,...........
00000020 FF FF FF FF FF FF FF FF FF FF FF FF 00 00 00 00 ................
00000030 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
00000040 68 69 73 69 2E 74 61 72 2E 6C 7A 6D 61 00 00 00 hisi.tar.lzma...
00000050 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
00000060 CC 01 00 00 21 A2 0C 00 7B 16 49 06 75 49 6D 61 ....!...{▬I.uIma
00000070 67 65 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ge..............
00000080 00 00 00 00 00 00 00 00 00 00 00 00 ED A3 0C 00 ................
00000090 94 A4 18 00 C5 B5 43 0C 77 65 62 73 2E 74 61 72 ..↑...C.webs.tar
000000A0 2E 6C 7A 6D 61 00 00 00 00 00 00 00 00 00 00 00 .lzma...........
000000B0 00 00 00 00 00 00 00 00 81 48 25 00 CD 8C 09 00 .........H%.....
000000C0 F8 32 C0 04 68 69 63 6F 72 65 2E 74 61 72 2E 6C .2..hicore.tar.l
000000D0 7A 6D 61 00 00 00 00 00 00 00 00 00 00 00 00 00 zma.............
000000E0 00 00 00 00 4E D5 2E 00 8B 7C 2D 00 2A 53 A5 16 ....N....|-.*S.▬
000000F0 64 76 72 43 6D 64 2E 74 61 72 2E 67 7A 00 00 00 dvrCmd.tar.gz...
00000100 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
00000110 D9 51 5C 00 B0 2E 00 00 31 84 18 00 73 74 61 72 .Q\.....1.↑.star
00000120 74 2E 73 68 00 00 00 00 00 00 00 00 00 00 00 00 t.sh............
00000130 00 00 00 00 00 00 00 00 00 00 00 00 89 80 5C 00 ..............\.
00000140 C9 04 00 00 36 95 01 00 72 61 6D 64 69 73 6B 2E ....6...ramdisk.
00000150 67 7A 00 00 00 00 00 00 00 00 00 00 00 00 00 00 gz..............
00000160 00 00 00 00 00 00 00 00 52 85 5C 00 A3 B6 0A 00 ........R.\.....
00000170 5A 24 55 05 76 65 72 73 69 6F 6E 63 74 72 2E 74 Z$U.versionctr.t
00000180 61 72 2E 6C 7A 6D 61 00 00 00 00 00 00 00 00 00 ar.lzma.........
00000190 00 00 00 00 F5 3B 67 00 70 0C 01 00 3D DB 85 00 .....;g.p...=...
000001A0 61 70 70 2E 74 61 72 2E 6C 7A 6D 61 00 00 00 00 app.tar.lzma....
000001B0 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
000001C0 65 48 68 00 1B D6 0C 00 0E FE 63 06
(ends)