[FFmpeg-user] Browser does not play webm videos concatenated with Ffmpeg

[Hans Georg Colle]

Hi,

here are the steps to reproduce the crash:

Concatenate two or more webm-videos with the demuxer method e. g.:
ffmpeg -f concat -i webm_dm.txt -c copy garten.webm
with webm_dm.txt containing
file garten1.webm
file garten2.webm

Place garten.webm in a video tag of a html5 page like
<video controls="controls">
<source src="garten.webm" type="video/webm" />
</video>

Now load this page into a Mozilla Firefox-Browser and start the video.

The video shows until it reaches the point where the second part, here
„garten2.webm“ has been added. Now Firefox stops showing the message „Kein
Video mit unterstütztem Format und Mime-Typ gefunden“ („No video with
supported format and MIME type found“). The video window can no longer be
operated by the controls and the page must be reloaded.

Additional information

I’m using Ffmpeg version 5.0.1-3+b1 Copyright (c) 2000-2022 the FFmpeg
developers built with gcc 11 (Debian 11.3.0-4)

The sequence of the pts-time-stamps, printed by
ffprobe -v error -hide_banner -of default=noprint_wrappers=1
-select_streams v:0 -show_entries packet=pts_time garten.webm
is strictly monotonous.

Aditionally, I concatenated the aforementioned videos garten1.webm and
garten2.webm with Avidemux and ran the result in the Firefox-Browser – this
time it showed the concatenated video from the beginning to the end.

You can watch garten.webm (garten1.webm and garten2.webm concatenated with
Ffmpeg) and adm.webm (garten1.webm and garten2.webm concatenated with
Avidemux) visiting https://colle-online.de/dokumente/concat_webm.html . You
can also download garten1.webm and garten2.webm from there and see the
outputs of ffprobe garten1.webm, ffprobe garten2.webm, ffprobe garten.webm,
and ffprobe adm.webm.

I wonder what may cause the different behaviour of that video files?

Greetings, Georg