On Tue, 21 May 2024, Lynne via ffmpeg-devel wrote:
On 21/05/2024 21:40, Marton Balint wrote:
On Tue, 21 May 2024, Lynne via ffmpeg-devel wrote:
On 21/05/2024 09:16, Marton Balint wrote:
On Sun, 19 May 2024, Lynne via ffmpeg-devel wrote:
On 19/05/2024 21:39, Marton Balint wrote:
On Sun, 19 May 2024, Lynne via ffmpeg-devel wrote:
This commit adds a decoder for the frequency-domain part of USAC.
[...]
+/* Finish later */
+static const enum AVChannel usac_ch_pos_to_av[64] = {
+ [0] = AV_CHAN_FRONT_LEFT,
+ [1] = AV_CHAN_FRONT_RIGHT,
+ [2] = AV_CHAN_FRONT_CENTER,
+ [3] = AV_CHAN_LOW_FREQUENCY,
+ [4] = AV_CHAN_BACK_LEFT, // unsure
+ [5] = AV_CHAN_BACK_RIGHT, // unsure
+ [6] = AV_CHAN_FRONT_LEFT_OF_CENTER,
+ [7] = AV_CHAN_FRONT_RIGHT_OF_CENTER,
+ [8] = 0, /* rear surround left is missing */
+ [9] = 0, /* rear surround right is missing */
+ [10] = AV_CHAN_BACK_CENTER,
+ [11] = AV_CHAN_SURROUND_DIRECT_LEFT,
+ [12] = AV_CHAN_SURROUND_DIRECT_RIGHT,
+ [13] = AV_CHAN_SIDE_LEFT, // fairly sure
+ [14] = AV_CHAN_SIDE_RIGHT, // fairly sure
+ [15] = AV_CHAN_WIDE_LEFT, // somewhat confident
+ [16] = AV_CHAN_WIDE_RIGHT, // somewhat confident
+ [17] = AV_CHAN_TOP_FRONT_LEFT,
+ [18] = AV_CHAN_TOP_FRONT_RIGHT,
+ [19] = AV_CHAN_TOP_FRONT_CENTER,
+ [20] = AV_CHAN_TOP_BACK_LEFT,
+ [21] = AV_CHAN_TOP_BACK_RIGHT,
+ [22] = AV_CHAN_TOP_BACK_CENTER,
+ [23] = AV_CHAN_TOP_SIDE_LEFT,
+ [24] = AV_CHAN_TOP_SIDE_RIGHT,
+ [25] = AV_CHAN_TOP_CENTER,
+ [26] = AV_CHAN_LOW_FREQUENCY, // actually LFE2
+ [27] = AV_CHAN_BOTTOM_FRONT_LEFT,
+ [28] = AV_CHAN_BOTTOM_FRONT_RIGHT,
+ [29] = AV_CHAN_BOTTOM_FRONT_CENTER,
+ [30] = 0, /* top left surround is missing */
+ [31] = 0, /* top right surround is missing */
+};
Some comment would be nice about the source of this table (which
document,
which table).
It looks very similar to the ISO channel positons used in mov_chan.
I
think we follow this mapping in most cases:
Left Surround is SIDE_LEFT
Right Surround is SIDE_RIGHT
Rear Surround Left is BACK_LEFT
Rear Surround Right is BACK_RIGHT
So in your table [4] and [5] should be SIDE, [8] and [9] should be
BACK.
[26] can be AV_CHAN_LOW_FREQUENCY_2, we do have that.
Yes, Left/Right Surround and Left/Right Side Surround will be the
same,
but those are not present in commonly used layouts at the same time.
Regards,
Marton
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Source of the table is ISO/IEC 23003-3, Table 74 — bsOutputChannelPos:
0 L left front FL front left
1 R right front FR front right
2 C center front FC front centre
3 LFE low frequency enhancement LFE1 low frequency effects-1
4 Ls left surround LS left surround
5 Rs right surround RS right surround
6 Lc left front center FLc front left centre
7 Rc right front center FRc front right centre
8 Lsr rear surround left BL back left
9 Rsr rear surround right BR back right
10 Cs rear center BC back centre
11 Lsd left surround direct LSd left surround direct
12 Rsd right surround direct RSd right surround direct
13 Lss left side surround SL side left
14 Rss right side surround SR side right
15 Lw left wide front FLw front left wide
16 Rw right wide front FRw front right wide
17 Lv left front vertical height TpFL top front left
18 Rv right front vertical height TpFR top front right
19 Cv center front vertical height TpFC top front centre
20 Lvr left surround vertical height rear TpBL top back left
21 Rvr right surround vertical height rear TpBR top back right
22 Cvr center vertical height rear TpBC top back centre
23 Lvss left vertical height side surround TpSiL top side left
24 Rvss right vertical height side surround TpSiR top side right
25 Ts top center surround TpC top centre
26 LFE2 low frequency enhancement 2 LFE2 low frequency effects-2
27 Lb left front vertical bottom BtFL bottom front left
28 Rb right front vertical bottom BtFR bottom front right
29 Cb center front vertical bottom BtFC bottom front centre
30 Lvs left vertical height surround TpLS top left surround
31 Rvs right vertical height surround TpRS top right surround
Third field is "Loudspeaker position", last field is "Loudspeaker
position according to IEC 100/1706/CDV/IEC 62574 (TC100)", each
prefixed
with an abbreviation.
I've added the source to the table comment in the code.
I've also fixed the SIDE/BACK/LFE2 issue in my github repo I linked
earlier.
Thanks. Later in the code when you actually use this I can see that you
are creating a native layout:
+ channel_config_idx = get_bits(gb, 5); /*
channelConfigurationIndex
*/
+ if (!channel_config_idx) {
+ /* UsacChannelConfig() */
+ uint8_t channel_pos[64];
+ uint8_t nb_channels = get_escaped_value(gb, 5, 8, 16); /*
numOutChannels */
+ if (nb_channels >= 64)
+ return AVERROR(EINVAL);
+
+ av_channel_layout_uninit(&ac->oc[1].ch_layout);
+ for (int i = 0; i < nb_channels; i++)
+ channel_pos[i] = get_bits(gb, 5); /* bsOutputChannelPos
*/
+
+ ac->oc[1].ch_layout.order = AV_CHANNEL_ORDER_NATIVE;
+ ac->oc[1].ch_layout.nb_channels = nb_channels;
+ ac->oc[1].ch_layout.u.mask = 0;
+
+ for (int i = 0; i < nb_channels; i++)
+ ac->oc[1].ch_layout.u.mask |= 1 <<
usac_ch_pos_to_av[channel_pos[i]];
+
+ av_channel_layout_copy(&avctx->ch_layout,
& ac->oc[1].ch_layout);
+ } else {
Probably you should create a custom layout here, because the channels
are
not necessary in native order. We already have a relatively simple way
to
do that and to fall back to native layouts if possible, here is an
example
copied from mov_chan:
ret = av_channel_layout_custom_init(ch_layout, channels);
if (ret < 0)
return ret;
for (i = 0; i < channels; i++) {
enum AVChannel id = layout_map[i].id;
ch_layout->u.map[i].id = (id != AV_CHAN_NONE ? id :
AV_CHAN_UNKNOWN);
}
return av_channel_layout_retype(ch_layout, 0,
AV_CHANNEL_LAYOUT_RETYPE_FLAG_CANONICAL);
So you should adapt this accodingly to aac.
Regards,
Marton
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According to the spec:
In case of multiple channel elements the index i of
bsOutputChannelPos[i] indicates the position in which the channel
appears in the bitstream.
So the channels will always be in native order, as far as I understand.
AV_CHANNEL_ORDER_NATIVE expects channels in the order of the channel IDs
in the AVChannel enum. Surely that is not the case here, unless the
decoder reorders the channels. Or what if an output position appears
multiple times?
Regards,
Marton
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It should be the case here, we shouldn't need reordering as NATIVE just lets
you specify what order the elements appear in the bitstream.
I don't get it.
bsOutputChannelPos[0] = 0
bsOutputChannelPos[1] = 1
will map to the same AVChannelLayout layout as
bsOutputChannelPos[0] = 1
bsOutptuChannelPos[1] = 0
which will be AV_CHANNEL_ORDER_NATIVE with a mask of 0x3, which means the
first channel is LEFT, the second channel is RIGHT.
Regards,
Marton
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