Fix DASH SegmentTimeline negative @r and Pattern, TTML sidecar sets with no contentType, HLS CHANNELS identifiers and Dolby channel masks; test against 408 public DASH/HLS/ISM manifests.
Unnamed tracks get the English language name (default region left out); subtitle tags gain the script their region implies (zh-TW -> zh-Hant-TW). Refs #169
Route titles with a dtsx/dtsy sample entry to MP4 via MP4Box, since Matroska has no CodecID for DTS-UHD. Add per-rendition HLS audio codec selection, fix merge_segments progress and its cleanup path.