[vlc-devel] [PATCH 1/4] es: move i_profile/i_level to audio and video format structs

Thomas Guillem thomas at gllm.fr
Tue Apr 3 10:03:33 CEST 2018

I would like to add a new information about DTSHD: it can be transmitted at different rates depending of the DTS extensions.

Right now, for 3.0, we assume that DTS-HD must be transmitted at 768 kHz. Some receiver won't accept this rate so VLC will fallback to DTS core, but maybe a lower rate could have worked (like 384 kHz).

In the DTS <=> SPDIF converter, we calculate the IEC61937 frame size depending on the rate configured by the output. If the rate is the highest (768 kHz), we'll be able to transmits all DTS extensions. At a lower rate, some DTSHD streams may fail to be transmitted but this lower rate will be likely accepted by more receivers.

So, for 4.0, I would like to have few distinctions for DTS/DTSHD:
 - DTS Core vs DTSHD
 - DTS HD: iec rate, frame_length or dtshd_subtype: this can be fetch from the packetizer, only one information is needed to guess everything else, cf. write_buffer_dtshd() in VLC.

On Mon, Apr 2, 2018, at 22:48, Jean-Baptiste Kempf wrote:
> Hello,
> On Mon, 2 Apr 2018, at 20:52, RĂ©mi Denis-Courmont wrote:
> > Yeah so I already answered that question in the email you quoted, I 
> > think. If you need to know to decode, then it's not the same syntax and 
> > thus not the same codec.
> > 
> > Of course, this leads to ambiguities, if you havea series of strict 
> > subsets. That's when you need to think what makes most practical sense.
> > 
> > Codecs can be identified by fourcc or by pair of fourcc and profile. 
> > It's a design decision how to convey entropy. It makes little/no sense 
> > proposing a new profile in audio/video format all the while we regret 
> > having RGB masks in addition to fourcc.
> > 
> > So again, if you need to distinguish the codec/syntaxes, you should use 
> > a different fourcc, if only to avoid reproducing the type of problems we 
> > have with RGB.
> > 
> > If you cannot distinguish at input, the you are screwed, with or without 
> > an extra profile field. And if it is a multidimensional problem, I am 
> > not clear how profile helps over fourcc either.
> Thanks for this detailed answer. I'll see with Thomas if we can do 
> something clever about this...
> -- 
> Jean-Baptiste Kempf -  President
> +33 672 704 734
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