• Rémi Denis-Courmont's avatar
    skiptags: properly conceal ID3/APE tags (fixes #18501) · 2c34ea75
    Rémi Denis-Courmont authored
    As most demuxers cannot handle tags at the beginning of their input
    streams, the demuxer code has automatically skipped them for a long
    Unfortunately, a number of demuxers also assume that the initial stream
    byte offset is zero (while some others seem to assume zero in some paths
    and not in others). This seems like a reasonable assumption. And even if
    it were not, fixing all affected stream filters and demuxers to perform
    only relative seeking seems impractical and unpalatable.
    This stream filter shifts the stream byte offset so that the tags are
    entirely invisible, and the demuxer can assume the start is at offset 0.
    Of couse, the tags must still be accessible to the meta extraction
    engine(s). The TagLib plugin uses "low-level" vlc_access_NewMRL() so it
    is not subject to stream filters, and not affected by this change.
    (This change does however remove tags from "demuxdump".)
    NOTE: On the one hand, this also enables demuxing a file format with
    embedded absolute file offsets, if the tags were prepended after muxing.
    On the other hand, it conversely breaks demuxing such a file format if
    the tags are added during muxing. As far as I know, tags are normally
    appended rather than prepended to avoid this ambiguity.