Le 25/10/2018 à 12:16 AM, Alex Converse a écrit :
On Wed, Oct 24, 2018 at 1:03 PM pkv.stream <pkv.str...@gmail.com> wrote:
Patch updated ; passes all FATE tests.
Comments from Alex Converse review incorporated (much thanks to him).
Hey,
I'm a bit concerned with the outputs this generates for low channel
count streams.
al17_44.mp4 has two front SCEs.
"ISO/IEC 13818-7:2005(E), 8.5.3.2 Explicit channel mapping using a
program_config_element" says:
Included in the PCE are “list of front channels”, using the rule
center outwards, left before right. In this list, a center channel
SCE, if any, must come first, and any other SCE’s must appear in
pairs, constituting an LR pair. If only two SCE’s are specified, this
signifies one LR stereophonic pair.
Before the patch we were getting L+R. With the patch we are getting
(FC+TFC) (0x2004).
I know of at least one commercial encoder that supports unpaired dual mono.
Do you know which spec the contains the eratta for top channels? There
doesn't seem to be much of value in Amd.6. Do you have any real
examples of a multichannel stream with a top center speaker or any
supporting documentation you could point me at?
Hi Alex
I'm only aware of 22.2 (chan_config = 13).
So given that top channels are not common, I 'm thinking of these
options in sniff_channel_order function :
- for chan_config == 0, keep only the decoding table and remove my
custom layout code;
- OR modify the custom layout code for chan_config == 0 , along lines
like that :
switch (num_front_channels_SCE + num_front_channels_CPE) {
case 1:
layout |= AV_CH_FRONT_CENTER;
break;
case 2:
layout |= AV_CH_FRONT_LEFT | AV_CH_FRONT_RIGHT ; // will
set the vector al17_44.mp4 back to FL+FR
break;
etc adding FLC, FRC, then TFC, and all the top channels
}
- OR keep the custom layout code so that SCE +SCE can be a dual mono as
FC + TFC.
Any option suits me; I'm agnostic on the matter.
As you wrote in your blog
<http://spectralhole.blogspot.com/2010/08/aac-bistream-flaws-part-1-channel-model.html>,
the channel spec is a big mess. ;-)
Best regards
pkv
Thanks,
Alex
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