Prefer opening codec by name instead of by ID.
Prefer opening codec by name instead of by ID.

This fixes a bug with actually using libxvid instead of mpeg4 because
both share the same CODEC_ID_MPEG4. This is similar to the recent
problem with ac3 selection in new versions of ffmpeg that have 2 ac3
encoders.

zzhhui/mlt,xzhavilla/mlt,mltframework/mlt,ttill/MLT-roto-tracking,wideioltd/mlt,anba8005/mlt,ttill/MLT,wideioltd/mlt,ttill/MLT-roto-tracking,siddharudh/mlt,ttill/MLT-roto-tracking,gmarco/mlt-orig,siddharudh/mlt,j-b-m/mlt,j-b-m/mlt,wideioltd/mlt,ttill/MLT-roto-tracking,siddharudh/mlt,xzhavilla/mlt,j-b-m/mlt,xzhavilla/mlt,mltframework/mlt,anba8005/mlt,siddharudh/mlt,ttill/MLT,ttill/MLT,mltframework/mlt,anba8005/mlt,gmarco/mlt-orig,ttill/MLT-roto,zzhhui/mlt,j-b-m/mlt,ttill/MLT-roto,zzhhui/mlt,ttill/MLT-roto,anba8005/mlt,ttill/MLT-roto-tracking,siddharudh/mlt,zzhhui/mlt,ttill/MLT,gmarco/mlt-orig,wideioltd/mlt,gmarco/mlt-orig,xzhavilla/mlt,anba8005/mlt,xzhavilla/mlt,wideioltd/mlt,anba8005/mlt,wideioltd/mlt,wideioltd/mlt,ttill/MLT,ttill/MLT,gmarco/mlt-orig,j-b-m/mlt,anba8005/mlt,gmarco/mlt-orig,xzhavilla/mlt,siddharudh/mlt,gmarco/mlt-orig,ttill/MLT-roto-tracking,siddharudh/mlt,siddharudh/mlt,ttill/MLT,zzhhui/mlt,ttill/MLT-roto-tracking,mltframework/mlt,ttill/MLT-roto,ttill/MLT,xzhavilla/mlt,mltframework/mlt,ttill/MLT-roto-tracking,wideioltd/mlt,ttill/MLT-roto,j-b-m/mlt,j-b-m/mlt,ttill/MLT,mltframework/mlt,ttill/MLT-roto,zzhhui/mlt,ttill/MLT-roto,ttill/MLT-roto,j-b-m/mlt,zzhhui/mlt,ttill/MLT-roto-tracking,xzhavilla/mlt,siddharudh/mlt,zzhhui/mlt,wideioltd/mlt,mltframework/mlt,j-b-m/mlt,xzhavilla/mlt,anba8005/mlt,gmarco/mlt-orig,ttill/MLT-roto,mltframework/mlt,zzhhui/mlt,j-b-m/mlt,mltframework/mlt,mltframework/mlt,anba8005/mlt,gmarco/mlt-orig