It's possible and common in Matrix chats to embed videos which are usually encoded in MP4 (H.264) format, but I was finding that videos were not playing for me in Neochat and I was only getting the audio instead. Also, Neochat was writing this line in the console while trying to reproduce the video: Warning: "No decoder available for type 'video/x-h264, stream-format=(string)avc, alignment=(string)au, level=(string)3, profile=(string)high, codec_data=(buffer)0164001effe100136764001eac1b1a81e06da6a0202020f08846a001000468ea43cb, width=(int)480, height=(int)864, pixel-aspect-ratio=(fraction)1/1, colorimetry=(string)bt709, framerate=(fraction)0/1, chroma-format=(string)4:2:0, bit-depth-luma=(uint)8, bit-depth-chroma=(uint)8, parsed=(boolean)true'." Which seems to indicate a missing GStreamer decoder. That matches comments on the Internet[1] that state that the libav plugin for GStreamer was missing. Indeed, that was fixed for me after merging media-plugins/gst-plugins-libav I don't know how this should be fixed. Either with an unconditional dependency, an optfeature or a conditional dependency based on the x264 USE flag, but given that bug 918509 rejected the possibility of making GStreamer dependency conditional, I guess that it makes sense making the media-plugins/gst-plugins-libav dependency also unconditional to make the GStreamer support as much complete as possible for the most common use cases. And for net-im/neochat to be able to effectively use media-plugins/gst-plugins-libav to decode H.264 videos, I guess it would need to make sure FFMpeg has been compiled with H.264 support by depending on media-video/ffmpeg[x264] [1] https://stackoverflow.com/a/54940466
