Rewrite seekable check in avformat.
Rewrite seekable check in avformat.

Now, alsa input works:
melt -profile dv_pal alsa:default

video4linux with alsa:
melt -profile quarter_15 video4linux2:/dev/video1 \
-track alsa:default -transition mix

And files over HTTP can handle seeking.

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