VP8 and H264 format stream not work

[gawinwong]

Description

• Library Version:ffmpeg4.0.6 with libvpx:latest libx264:latest
• ROS Version:melodic
• Platform / OS:ubuntu 18.04

Steps To Reproduce

I build web_video_server with ffmpeg4.0.6, and grab a topic named /usb_cam/image_raw from ros.
When I use the stream url http://0.0.0.0:8080/stream?topic=/usb_cam/image_raw&type=h264 or http://0.0.0.0:8080/stream?topic=/usb_cam/image_raw&type=vp8, it occurs en 500 error, and the console log says "exception: Error looking up output format".

Expected Behavior
display vp8 or h264 stream

Actual Behavior
exception: Error looking up output format

[hosome17]

Have you solve it yet? I have the same problem.