[FFmpeg-user] FFMpeg save to file vs output to multicast, what is different?

Ibrahim Tachijian barhom at gmail.com
Wed Feb 12 13:15:26 CET 2014

Consider the two following command lines:

./testffmpeg -y -analyzeduration 1000000 -i udp:// -g 25
-c:v libvpx -b:v 1M -c:a libvorbis -f webm file.webm


./testffmpeg -y -analyzeduration 1000000 -i udp:// -g 25
-c:v libvpx -b:v 1M -c:a libvorbis -f webm udp://


Since you are sending the 2nd alternative to a multicast address you need
some software that can listen in on the multicast address and save it to
file. You can use multicat for this

Run this to reproduce:

1. multicast -uU @ multicat.webm
This will now listen to any incoming data to and save it
to file named multicat.webm
2. Rung first and second commandline.

The end results are two files file.web and multicat.webm where the only
difference was one was written to file directly and the other was sent to
multicast address and read back and then written to file.

file.webm is playable fine.
multicat.webm does not play.

I see no reason why both wouldn't work and its driving me crazy.

Ibrahim Tachijian

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