[IMPROVEMENT] Add Default X-TIMESTAMP-MAP Header When No Subtitles Are Present

[AbHash-RixE]

CCExtractor version: 0.94

Necessary information

• Is this a regression (i.e. did it work before)? NO
• What platform did you use? Linux
• What were the used arguments? ./ccextractor --timestamp-map --out=webvtt output_clean.ts

Description

Current Behavior: When there are no subtitles in the .ts file, the tool (CCExtractor) produces an empty .webvtt file ,
i.e no X-TIMESTAMP-MAP header is produced . This is expected behavior, as no subtitles are present.

Desired Behavior: To add a default X-TIMESTAMP-MAP header in the .webvtt file even when no subtitles are present,
i.e X-TIMESTAMP-MAP=MPEGTS:0,LOCAL:00:00:00.000.

This would ensure that the .webvtt file is consistently formatted, even when there are no subtitles present, which is necessary for HLS stream compatibility.

[bbgdzxng1]

@AbHash-RixE... Proposed sharpening of your desired behavior statement...

Desired Behavior: If --timestamp-map is specified, add a X-TIMESTAMP-MAP header in the .webvtt file even when no subtitles are present,
i.e

WEBVTT
X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000

(I'm just nitting "default", because technically all X-TIMESTAMP-MAP headers are invalid WebVTT, they just happen to be valid HLS, due to a long-running saga around the exact definition of WebVTT metadata headers). Background:
w3c/webvtt#485 (comment)
https://mailarchive.ietf.org/arch/msg/hls-interest/MzTHEqH3FVE5E3chn8ULjUon9b8/

And secondly, nitting that from a format perspective, HLS RFC defines that LOCAL is the first field, MPEGTS is the second.

X-TIMESTAMP-MAP=LOCAL:<cue time>,MPEGTS:<MPEG-2 time>

[AbHash-RixE]

Hi @bbgdzxng1, thank you for the clarification and pointing out the correct field order ( LOCAL before MPEGTS ) as
per the HLS spec — | wasn't aware of that .
I'll update the desired behavior.

[AbHash-RixE]

Hi @bbgdzxng1,
When I run ./ccextractor --timestamp-map --out=webvtt BBC1.ts i get (when sub is present)
X-TIMESTAMP-MAP=MPEGTS:5215387095,LOCAL:00:00:00.000
You previously mentioned the correct format (for when no subtitles are present) should be:
X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000 .
However, the output differs in order. This has a different field order. I'm a bit confused — is ccextractor currently producing the wrong order when subtitles are present?

[bbgdzxng1]

@AbHash-RixE

However, the output differs in order. This has a different field order. I'm a bit confused — is ccextractor currently producing the wrong order when subtitles are present?

Technically, yes. Reality is that it is just a pedantic nit. It will make no practical difference either way.

I prepped a PR which you can steal as part of your improvement for empty cues. bbgdzxng1#1

The change just brings it in line with spec.