SCTE 35 is parsing errors

[sbowman]

I tried parsing a SCTE 35 signal on the web site, and it's giving me much different information than other SCTE 35 parsers.

I tried this signal:

/DAxAAAAAAAAAP/wFAUAAAD5f+//vbeKtH4AUmNiAAAAAAAMAQpDVUVJUJ8xMjEqiKYAKA==

What this library reported:

{
	"tableId": 252,
	"selectionSyntaxIndicator": false,
	"privateIndicator": false,
	"sectionLength": 49,
	"protocolVersion": 0,
	"encryptedPacket": false,
	"encryptedAlgorithm": 0,
	"ptsAdjustment": 0,
	"cwIndex": 0,
	"tier": 4095,
	"spliceCommandLength": 20,
	"spliceCommandType": 5,
	"spliceCommand": {
		"spliceEventId": 249,
		"spliceEventCancelIndicator": false,
		"outOfNetworkIndicator": true,
		"programSpliceFlag": true,
		"durationFlag": true,
		"spliceImmediateFlag": false,
		"spliceTime": {
			"specified": false
		},
		"breakDuration": {
			"autoReturn": true,
			"duration": 7374287998
		},
		"uniqueProgramId": 82,
		"available": 99,
		"expected": 98
	},
	"descriptorLoopLength": 12,
	"descriptor": [
		{
			"spliceDescriptorTag": 1,
			"descriptorLength": 10,
			"indentifier": "CUEI"
		}
	],
	"crc": 2292580392
}

What other SCTE 35 tools report:

splice_info_section() {
    table_id: 0x00fc (252)
    section_syntax_indicator: 0
    private_indicator: 0
    section_length: 0x31 (49 bytes)
}
protocol_version: 0x00 (0)
encrypted_packet: false
encryption_algorithm: 0x00 (No encryption)
pts_adjustment: 0x000000000 (0 ticks, 0.000 secs)
cw_index: 0x00 (0)
tier: 0xfff (4095)
splice_command_length: 0x014 (20 bytes)
splice_command_type: 0x05
splice_insert() {
    splice_event_id: 0x00f9 (249)
    splice_event_cancel_indicator: false
    out_of_network_indicator: true
    program_splice_flag: true
    duration_flag: true
    splice_immediate_flag: false
    time_specified_flag: true
    pts_time: 0x1bdb78ab4 (7477889716 ticks, 83087.664 secs)
    auto_return: false
    duration: 0x526362 (5399394 ticks, 59.000000 secs)
    unique_program_id: 0x0000 (0)
    avail_num: 0x00 (0)
    avails_expected: 0x00 (0)
}
descriptor_loop_length: 0x000c (12 bytes)
dtmf_descriptor() {
    splice_descriptor_tag: 0x01 (1)
    descriptor_length: 0x0a (10 bytes)
    identifier: 0x43554549 (1129661769 CUEI)
    preroll: 0x50 (80/10 s)
    dtmf_count: 0x4 (4 chars)
    dtmf_chars: 121*
}

Splice time is specified, but this library says it's not. Break duration in this library is wrong. Program ID is wrong. Avails are all wrong.

[sbowman]

Here's a good resource to use for comparison:

https://openidconnectweb.azurewebsites.net/Cue

[avhetman]

@sbowman I believe the parsing error you mentioned has now been resolved in the latest release, could you please confirm?

[avhetman]

@futzu could you be more specific as to what properties are not parsed as expected?

[futzu]

I apologize, I wasn't trying to be rude.. I didn't mean to offend.

[avhetman]

No need to apologize, no offence taken at all, just trying to understand how to improve this parser :)

[avhetman]

Closing due to inactivity

[shruggingatlas]

Hi — I came across this issue while testing SCTE-35 signals from various sources against a parser I've been working on, and I believe the reporter's observation is correct. The discrepancy appears to come from a bit-alignment issue when parsing the splice_time() structure inside splice_insert().

For this signal (/DAxAAAAAAAAAP/wFAUAAAD5f+//vbeKtH4AUmNiAAAAAAAMAQpDVUVJUJ8xMjEqiKYAKA==), the fields should parse as follows per §9.7.2 of SCTE 35:

splice_event_id:          0x000000F9 (249)
out_of_network_indicator: 1
program_splice_flag:      1
duration_flag:            1
splice_immediate_flag:    0

Since program_splice_flag=1 and splice_immediate_flag=0, a splice_time() follows:

time_specified_flag:      1  ← (not 0)
pts_time:                 0x1BDB78AB4 (~83,087.66 s)

auto_return:              0
duration:                 5,399,394 ticks (~59.99 s)
unique_program_id:        0
avail_num:                0
avails_expected:          0

It looks like the parser may be losing bit alignment after reading the flags byte (the byte containing out_of_network_indicator through the reserved bits). By the time it reaches splice_time(), it reads time_specified_flag as 0 instead of 1, which causes all the subsequent fields (break_duration, unique_program_id, avail_num, avails_expected) to shift and produce incorrect values.

Other parsers (TSDuck, threefive) agree on the values above. I hope this is helpful for anyone looking into a fix — happy to provide more detail if it would be useful.