2025-03-31, 07:22 PM
I tested it again, and yes there is still a subtitle sync issue when using fMP4with your modified jellyfin-web. It starts playing correctly, then after a few seeks back and forth, subtitle gets ahead of the video and audio. It's faster to replicate the issue with an external .srt (but it happens with embedded .srt too, just takes a few more seeks). I replicated the issue with a DV P8 mkv file and both embedded and external .srt subtitle.
Regardless of this issue, I remember one more that is present when using fMP4 with the official jellyfin-web, and that is that it doesn't apply audio delay if it exists in an mkv file. This mkv file has DV P8 video and EAC3 audio from a different source, that is delayed 2s2ms to the video. This is what mediainfo looks like.
![[Image: attachment.php?aid=3496]](https://forum.jellyfin.org/attachment.php?aid=3496)
That delay is completely ignored when using fMP4, so audio plays out of sync. I replicated the same issue with your modified jellyfin-web.
Just to be clear, both of those issues are present currently in the official build when using fMP4 and were not caused by using hls.js. As of now, in the official version, the only way around those issues is remuxing to .ts container instead of .mp4, which gives us dolby vision, stable playback and fast forwarding, synced subtitles, and applied audio delay if it exist in a .mkv file, but also gives us false (?) Atmos and stereo sound only. Using your modified jellyfin-web and fMP4 we get fixed dolby vision p8, multichannel audio (without atmos) and stable fast forwarding, but we reintroduce issues with subtitle getting out of sync and ignored audio delay. We also lose dolby vision completely when using .ts container.
I tested on LG C2, WebOS 23.20.62. Jellyfin server for Windows 10.10.6 and latest WebOS client.
Regardless of this issue, I remember one more that is present when using fMP4 with the official jellyfin-web, and that is that it doesn't apply audio delay if it exists in an mkv file. This mkv file has DV P8 video and EAC3 audio from a different source, that is delayed 2s2ms to the video. This is what mediainfo looks like.
That delay is completely ignored when using fMP4, so audio plays out of sync. I replicated the same issue with your modified jellyfin-web.
Just to be clear, both of those issues are present currently in the official build when using fMP4 and were not caused by using hls.js. As of now, in the official version, the only way around those issues is remuxing to .ts container instead of .mp4, which gives us dolby vision, stable playback and fast forwarding, synced subtitles, and applied audio delay if it exist in a .mkv file, but also gives us false (?) Atmos and stereo sound only. Using your modified jellyfin-web and fMP4 we get fixed dolby vision p8, multichannel audio (without atmos) and stable fast forwarding, but we reintroduce issues with subtitle getting out of sync and ignored audio delay. We also lose dolby vision completely when using .ts container.
I tested on LG C2, WebOS 23.20.62. Jellyfin server for Windows 10.10.6 and latest WebOS client.