[FFmpeg-devel] [PATCH]lavc/mlp_parse: Read wordlength from 0xba streams

[Hendrik Leppkes]

On Fri, Feb 14, 2020 at 11:45 AM Carl Eugen Hoyos <ceffmpeg at gmail.com> wrote:
>
> Am Fr., 14. Feb. 2020 um 01:26 Uhr schrieb Hendrik Leppkes
> <h.leppkes at gmail.com>:
> >
> > On Fri, Feb 14, 2020 at 12:29 AM Carl Eugen Hoyos <ceffmpeg at gmail.com> wrote:
> > >
> > > Attached patch allows detecting s16 truehd streams encoded with
> > > FFmpeg, only tested with FFmpeg's encoder, I did not look into any
> > > specification.
> >
> > According to Dolbys Bitstream specification this read does not seem
> > right. It reads half of a reserved field and 3 single-bit control
> > fields - in a structure called "channel meaning", which otherwise only
> > includes fields on channel assignment and interpretation, so this
> > field being in there seems weird.
> > Also, why would they code a literal value, and not a lookup table with
> > fewer bits like the 0xbb case does?
> >
> > Unless we can find an actual real-world sample from a licensed encoder
> > that can confirm the presence and accuracy of this field, I'm going to
> > assume its not correct. It looks to me like it may be writing a MLP
> > (ie. 0xbb) header, and not a TrueHD header - beyond the first
> > differences, anyway. The high-level bitstream specification was not
> > available when mlpenc.c was initially written.
>
> Thank you for looking into this!
> Is there a link to the high-level bitstream specification?
>

Its here:
https://developer.dolby.com/globalassets/technology/dolby-truehd/dolbytruehdhighlevelbitstreamdescription.pdf

- Hendrik