If you run 'while read aurl ; do youtube-dl "${aurl}"; done < path_to_batch_file' (batch_file contains one url per line that uses the hls downloader) each call to youtube-dl consumed some characters and 'read' would assing to 'aurl' a non valid url
(This is the same problem that was fixed for the ffmpeg postprocessors in cffcbc02de)
Should make downloading with filters more precise and easier, ie. bestvideo[vcodec=h264]. By default a lot of codecs are specified as avc1.xxxxxx and unique for each format, which makes them unusable for bestvideo selection.