avformat/hls: parse #EXT-X-MEDIA-SEQUENCE only once
avformat/http: read exact bytes at end of stream to avoid being blocked
avformat/mov: prefer nearest sample as next sample
avformat/http: try to fix missing Content-Range
avformat/hls: compare seek_timestamp to duration + start_time
avformat/hls: seek to last segment if beyond duration
avformat/hls: disable seek within segment
avformat/hls: add flag AVFMT_TS_DISCONT
avformat/hls: retry connect for segment
avformat/aviobuf: enlarge IO_BUFFER_SIZE and SHORT_SEEK_THRESHOLD
avformat/hls: skip invalid variant
avformat/hls: fix duration
avformat/concatdec: close previous segment only after new segment is open successfully

Later call to concat_read_packet could cause NULL pointer access.