libav only supports encoding DV with 2 channel, 48kHz, 16bit PCM audio but avmux_dv reports supporting a wide range of frequencies.

-----------------------------------------
$ gst-inspect-1.0 avmux_dv

<snip>

  SINK template: 'audio_%u'
    Availability: On request
      Has request_new_pad() function: 0x7fc03826a7f0
    Capabilities:
      audio/x-raw
               channels: [ 1, 2 ]
                   rate: [ 4000, 96000 ]
                 format: S16LE
                 layout: interleaved

<snip>

$
-----------------------------------------


The correct output would be;
-----------------------------------------
$ gst-inspect-1.0 avmux_dv

<snip>

  SINK template: 'audio_%u'
    Availability: On request
      Has request_new_pad() function: 0x7fc03826a7f0
    Capabilities:
      audio/x-raw
               channels: [ 2 ]
                   rate: [ 48000 ]
                 format: S16LE
                 layout: interleaved

<snip>

$
-----------------------------------------


If you fail to send the correct 2 channel, 48kHz audio you get an error something like;
-----------------------------------------
Setting pipeline to PAUSED ...
Pipeline is live and does not need PREROLL ...
Setting pipeline to PLAYING ...
New clock: GstSystemClock
ERROR: from element /GstPipeline:pipeline0/ffmux_dv:dvmux: Could not configure supporting library.
Additional debug info:
gstffmpegmux.c(665): gst_ffmpegmux_collected (): /GstPipeline:pipeline0/ffmux_dv:dvmux:
Failed to write file header - check codec settings
-----------------------------------------


##############################################
# Where are these caps coming from?
##############################################

The caps come from the following function in gstavcodecmap.c;
-----------------------------------------
static GstCaps *
gst_ff_aud_caps_new (AVCodecContext * context, AVCodec * codec,
    enum AVCodecID codec_id, gboolean encode, const char *mimetype,
    const char *fieldname, ...)
{
-----------------------------------------

They seem to be from hitting a default else on the following lines in gstavcodecmap.c;
-----------------------------------------
706    } else {
707      gst_caps_set_simple (caps, "rate", GST_TYPE_INT_RANGE, 4000, 96000, NULL);
708    }
-----------------------------------------


##############################################
# libavformat DV audio support info
##############################################

From libavformat/dvenc.c
-----------------------------------------
    /* Some checks -- DV format is very picky about its incoming streams */
    if (!vst || vst->codec->codec_id != AV_CODEC_ID_DVVIDEO)
        goto bail_out;
    for (i=0; i<c->n_ast; i++) {
        if (c->ast[i] && (c->ast[i]->codec->codec_id    != AV_CODEC_ID_PCM_S16LE ||
                          c->ast[i]->codec->sample_rate != 48000 ||
                          c->ast[i]->codec->channels    != 2))
            goto bail_out;
    }

-----------------------------------------

static int dv_write_header(AVFormatContext *s)
{
    if (!dv_init_mux(s)) {
        av_log(s, AV_LOG_ERROR, "Can't initialize DV format!\n"
                    "Make sure that you supply exactly two streams:\n"
                    "     video: 25fps or 29.97fps, audio: 2ch/48kHz/PCM\n"
                    "     (50Mbps allows an optional second audio stream)\n");
        return -1;
    }
    return 0;
}

-----------------------------------------