[FFmpeg-devel] [PATCH] avformat/mov: parse 3gpp titl from media or track udta

[Jan Ekström]

On Wed, Jul 21, 2021 at 8:28 PM Jan Ekström <jeebjp at gmail.com> wrote:
>
> Seems to be:
> * Utilized by Handbrake for track titling
> * Actually defined as "title for the media"
>
> Definition from 3GPP TS 26.244 follows:
>
> Field               Type                Details                             Value
> BoxHeader.Size      Unsigned int(32)                                        BOX_SIZE
> BoxHeader.Type      Unsigned int(32)                                        'titl'
> BoxHeader.Version   Unsigned int(8)                                         0
> BoxHeader.Flags     Bit(24)                                                 0
> Pad                 Bit(1)                                                  0
> Language            Unsigned int(5)[3]  Packed ISO-639-2/T language code
> Title               String              Text of title
>
> Semantics:
>
> Language: declares the language code for the following text. See
> ISO 639-2/T for the set of three character codes. Each character
> is packed as the difference between its ASCII value and 0x60.
>
> The code is confined to being three lower-case letters, so these
> values are strictly positive.
>
> Title: null-terminated string in either UTF-8 or UTF-16 characters,
> giving a title information. If UTF-16 is used, the string shall
> start with the BYTE ORDER MARK (0xFEFF).
> ---

A sample for this sort of metadata can be seen with
https://0x0.st/-zjq.m4v , which was posted at
https://github.com/mpv-player/mpv/issues/8488 .

The sample contains both "name" and "titl" boxes:
[udta: User Data Box]
    position = 3991500
    size = 71
    [name]
        position = 3991508
        size = 28
    [titl]
        position = 3991536
        size = 35

...out of which if I read QTFF documentation correctly "name" should
not be utilized for user-facing naming, and "titl" is actually a
user-facing metadata box. Thus I implemented the latter.

Jan