avconv converting videos in really bad quality I have this linux command line app called avcon. It is used to converting files. For instance if I have a file called video.mp4 I can run avconv -i video.mp4 video.ogg and it will convert this video.mp4 to video.ogg. 

So my problem(question):
Whenever it converts any file the output file's quality is super bad compared to the original video (the input video). How can I get around with that? I mean how can I convert the file and still get the same quality?  

If this is not possible using this app. Can anybody suggest anything else for converting video files using the command line?
Get ffmpeg

Download a recent build of ffmpeg. Binaries for Windows, Linux, and OS X are available on the FFmpeg Download page. Development is very active and there is no need to use buggy avconv (note that this answer was written for ffmpeg, so I'm not sure if any examples will work with avconv).

Theora video &amp; Vorbis audio in OGG

Theora is old and has been superseded in many cases by VP8/VP9 video in WebM (see example below), so there are few reasons to use Theora in OGG/OGV.

ffmpeg -i input -c:v libtheora -q:v 5 -c:a libvorbis -q:a 5 output.ogv



-q:v – video quality. Range is 0-10, where 10 is highest quality. 5-7 is a good range to try. If you omit -q:v then ffmpeg will use the default of -b:v 200k which will most likely provide a poor quality output, and libtheora may drop/skip frames if the bitrate is too low. 
-q:a – audio quality. Range is 0-10, where 10 is highest quality. 3-6 is a good range to try. Default is -q:a 3. 


Adapted from FFmpeg Wiki: A Brief Theora and Vorbis Encoding Guide.

VP8 video &amp; Vorbis audio in WebM

ffmpeg -i input -c:v libvpx -qmin 0 -qmax 50 -crf 5 -b:v 1M -c:a libvorbis -q:a 5 output.webm



See FFmpeg Wiki: VP8 Encoding Guide and VP8 Encode Parameter Guide to optimize your command.
If you want to encode VP9 video, then use -c:v libvpx-vp9. It is currently a slow encoder.