FFmpeg 4 is failing to install on CI

[scotts]

Example: https://github.com/meta-pytorch/torchcodec/actions/runs/18540256242/job/52847516401?pr=967

The error is:

ffmpeg: error while loading shared libraries: libiconv.so.2: cannot open shared object file: No such file or directory
Error: Process completed with exit code 127.

I've seen this locally in my own environments when I had some incompatibilities between packages or packages were missing.

[traversaro]

I am not 100% sure, but I suspect this is again a consequence of mixing defaults and conda-forge, see also #518 (comment) and #951 (comment) .

[traversaro]

I am not 100% sure, but I suspect this is again a consequence of mixing defaults and conda-forge, see also #518 (comment) and #951 (comment) .

Indeed, this seems confirmed by CI: #975 . As this is the third instance of this problem, perhaps we may want to just switch all CI workflows to avoid mixing defaults and conda-forge channels.