The VideoLAN Forums

attempted both h264 and h265 mp4's from a m3u8
the m3u8 file plays just fine, tried on multiple computers as well, the outcome is the first 3 seconds of a 2 minute video

this is verbose version of log - I manually cut to fit post

main error: cannot add a new stream (unsupported while muxing to this format). You can try increasing sout-mux-caching value
main error: cannot continue streaming due to errors with codec mp4a

x264 debug: version x264 0.155.X
x264 info: using SAR=1/1
x264 warning: MB rate (172800000) > level limit (16711680)
x264 info: using cpu capabilities: MMX2 SSE2Fast SSSE3 SSE4.2 AVX FMA3 BMI2 AVX2
x264 info: profile High, level 6.2
main debug: using encoder module "x264"
main error: cannot add a new stream (unsupported while muxing to this format). You can try increasing sout-mux-caching value
stream_out_transcode error: cannot add this stream
main error: cannot continue streaming due to errors with codec h264


d3d11va warning: failed to get the 0 MatchingDeviceId (2)
ts warning: No PCR received for program 1, set up workaround using pid 258
faad warning: decoded zero sample

Try to increase the Stream Output Muxer Cache value in Tools -> Preferences (Show settings = All) -> Stream output

I increased it from 1500 to 9000 ms. No difference.
Is it possible that the stream contains a stop code that prevents one from saving it?

More likely you got a stream cutoff and/or the encoder can't catch up and fail to encode at real time.
Use the Record button instead.