decklink: support all valid numbers of audio channels

As it is already written in the documentation, BMD DeckLink cards
are capable of capturing 2, 8 or 16 audio channels (for SDI Inputs).
Currently the value is hardcoded to 2. Introduces new option.
Reviewed-by: Deti Fliegl <deti@fliegl.de>
Signed-off-by: Matthias Hunstock <atze@fem.tu-ilmenau.de>
Signed-off-by: Marton Balint <cus@passwd.hu>

doc/indevs.texi

@@ -218,7 +218,8 @@ On Windows, you need to run the IDL files through @command{widl}.
 DeckLink is very picky about the formats it supports. Pixel format is
 uyvy422 or v210, framerate and video size must be determined for your device with
 @command{-list_formats 1}. Audio sample rate is always 48 kHz and the number
-of channels can be 2, 8 or 16.
+of channels can be 2, 8 or 16. Note that all audio channels are bundled in one single
+audio track.
 
 @subsection Options
 
@@ -246,6 +247,10 @@ can use the special @option{all} constant to select all possible lines, or
 receivers. Capturing teletext only works for SD PAL sources in 8 bit mode.
 To use this option, ffmpeg needs to be compiled with @code{--enable-libzvbi}.
 
+@item channels
+Defines number of audio channels to capture. Must be @samp{2}, @samp{8} or @samp{16}.
+Defaults to @samp{2}.
+
 @end table
 
 @subsection Examples
@@ -276,6 +281,12 @@ Capture video clip at 1080i50 10 bit:
 ffmpeg -bm_v210 1 -f decklink -i 'UltraStudio Mini Recorder@@11' -acodec copy -vcodec copy output.avi
 @end example
 
+@item
+Capture video clip at 1080i50 with 16 audio channels:
+@example
+ffmpeg -channels 16 -f decklink -i 'UltraStudio Mini Recorder@@11' -acodec copy -vcodec copy output.avi
+@end example
+
 @end itemize
 
 @section dshow

libavdevice/decklink_common_c.h

@@ -33,6 +33,7 @@ struct decklink_cctx {
     int64_t teletext_lines;
     double preroll;
     int v210;
+    int audio_channels;
 };
 
 #endif /* AVDEVICE_DECKLINK_COMMON_C_H */

libavdevice/decklink_dec.cpp

@@ -466,6 +466,17 @@ av_cold int ff_decklink_read_header(AVFormatContext *avctx)
     }
 #endif
 
+    /* Check audio channel option for valid values: 2, 8 or 16 */
+    switch (cctx->audio_channels) {
+        case 2:
+        case 8:
+        case 16:
+            break;
+        default:
+            av_log(avctx, AV_LOG_ERROR, "Value of channels option must be one of 2, 8 or 16\n");
+            return AVERROR(EINVAL);
+    }
+
     iter = CreateDeckLinkIteratorInstance();
     if (!iter) {
         av_log(avctx, AV_LOG_ERROR, "Could not create DeckLink iterator\n");
@@ -543,7 +554,7 @@ av_cold int ff_decklink_read_header(AVFormatContext *avctx)
     st->codec->codec_type  = AVMEDIA_TYPE_AUDIO;
     st->codec->codec_id    = AV_CODEC_ID_PCM_S16LE;
     st->codec->sample_rate = bmdAudioSampleRate48kHz;
-    st->codec->channels    = 2;
+    st->codec->channels    = cctx->audio_channels;
     avpriv_set_pts_info(st, 64, 1, 1000000);  /* 64 bits pts in us */
     ctx->audio_st=st;
 
@@ -587,7 +598,8 @@ av_cold int ff_decklink_read_header(AVFormatContext *avctx)
         ctx->teletext_st = st;
     }
 
-    result = ctx->dli->EnableAudioInput(bmdAudioSampleRate48kHz, bmdAudioSampleType16bitInteger, 2);
+    av_log(avctx, AV_LOG_VERBOSE, "Using %d input audio channels\n", ctx->audio_st->codec->channels);
+    result = ctx->dli->EnableAudioInput(bmdAudioSampleRate48kHz, bmdAudioSampleType16bitInteger, ctx->audio_st->codec->channels);
 
     if (result != S_OK) {
         av_log(avctx, AV_LOG_ERROR, "Cannot enable audio input\n");

libavdevice/decklink_dec_c.c

@@ -35,6 +35,7 @@ static const AVOption options[] = {
     { "teletext_lines", "teletext lines bitmask", OFFSET(teletext_lines), AV_OPT_TYPE_INT64, { .i64 = 0   }, 0, 0x7ffffffffLL, DEC, "teletext_lines"},
     { "standard",     NULL,                                           0,  AV_OPT_TYPE_CONST, { .i64 = 0x7fff9fffeLL}, 0, 0,    DEC, "teletext_lines"},
     { "all",          NULL,                                           0,  AV_OPT_TYPE_CONST, { .i64 = 0x7ffffffffLL}, 0, 0,    DEC, "teletext_lines"},
+    { "channels",     "number of audio channels", OFFSET(audio_channels), AV_OPT_TYPE_INT , { .i64 = 2   }, 2, 16, DEC },
     { NULL },
 };