Abrupt transition between fmp4 playlists after merging

[Trassive]

I have a single video file that I split at keyframes and then transcoded each chunk in parallel, using the appropriate output_ts_offset to maintain timing. Despite this i see an abrupt transition from one part to another part

Observations:

• If I merge init_1.mp4 + 2_720p_000.m4s, the resulting file has PTS near zero.
• If I merge init_2.mp4 + 2_720p_000.m4s, the resulting file has PTS near the expected value in the original source video (<±1 sec).

What I Tried:

• Reusing the same init.mp4 across all segments (i.e., skipping #EXT-X-DISCONTINUITY) , but the abrupt transition still occurs.

Ensuring that output_ts_offset is properly set during transcoding to align timestamps.

#EXTM3U
#EXT-X-VERSION:7
#EXT-X-TARGETDURATION:2
#EXT-X-MEDIA-SEQUENCE:0
#EXT-X-PLAYLIST-TYPE:EVENT
#EXT-X-INDEPENDENT-SEGMENTS
#EXT-X-MAP:URI="init_1.mp4"
#EXTINF:2.000000,
1_720p_000.m4s
#EXTINF:2.000000,
1_720p_001.m4s
...
// some more segments
......
#EXTINF:0.360000,
1_720p_011.m4s
#EXT-X-DISCONTINUITY
#EXT-X-MAP:URI="init_2.mp4"
#EXTINF:2.000000,
2_720p_000.m4s
#EXTINF:2.000000,
2_720p_001.m4s
...
// some more segments
......
#EXTINF:1.000000,
2_720p_010.m4s

[robwalch]

What I Tried:

Reusing the same init.mp4 across all segments (i.e., skipping #EXT-X-DISCONTINUITY) , but the abrupt transition still occurs.

Was the init segment repeated in the playlist? If the init segments are identical, you do not need to repeat them. If the timestamps are contiguous, you don't need a discontinuity tag.

Inserting init segments can introduce interruptions in decoding and rendering so only introduce them and discontinuities in the playlist when necessary.

The interruption is not caused by HLS.js. It is the browser's responsibility to decode and render the buffered media as seamlessly as possible.

If you are producing content with audio, it will be more noticeable.

[Trassive]

They were part of the same file which was splitted at keyframes and starts from 0, to compensate timestamp issue we created seperate playlist with output_ts_offset flag requiring us to use the seperate init.mp4 for merging all the playlist, apart from timestamp rest of the things are identical in init.mp4. I am aware that HLS.js is not the issue here, could you suggest any workaround to mitigate these abrupt transition.

[robwalch]

Include only one init segment at the start of the merged playlist.

[Trassive]

That also resulted in an abrupt transition. While investigating the issue, I discovered that init.mp4 together with the .m4s segment determines the presentation time.
To verify this, I combined init_1.mp4 (from the first playlist) with 2_720p_000.m4s (from the second playlist) into combined.mp4 which had a presentation timestamp (PTS) near zero, but it wasn't the case when i tried merging the same segment with the init_2.mp4 (from second playlist) as mentioned in observation of question