https://bugs.launchpad.net/ubuntu/+source/gst-plugins-bad1.0/+bug/1299376/comments/6

$ gst-launch-1.0 -v -e v4l2src device=/dev/video0 ! capsfilter name=mycapsfilter caps=video/x-raw,width=1280,height=720 ! x264enc tune=zerolatency ! queue ! mp4mux name=m ! filesink location=/tmp/file.mp4 alsasrc device=hw:2,0 ! audioconvert ! audioresample ! avenc_aac ! queue ! m.
Setting pipeline to PAUSED ...
Pipeline is live and does not need PREROLL ...
Setting pipeline to PLAYING ...
New clock: GstAudioSrcClock
/GstPipeline:pipeline0/GstAlsaSrc:alsasrc0: actual-buffer-time = 200000
/GstPipeline:pipeline0/GstAlsaSrc:alsasrc0: actual-latency-time = 10000
/GstPipeline:pipeline0/GstAlsaSrc:alsasrc0.GstPad:src: caps = "audio/x-raw\,\ format\=\(string\)S16LE\,\ layout\=\(string\)interleaved\,\ rate\=\(int\)44100\,\ channels\=\(int\)1"
/GstPipeline:pipeline0/GstAudioConvert:audioconvert0.GstPad:src: caps = "audio/x-raw\,\ layout\=\(string\)interleaved\,\ rate\=\(int\)44100\,\ format\=\(string\)F32LE\,\ channels\=\(int\)1"
/GstPipeline:pipeline0/GstAudioResample:audioresample0.GstPad:src: caps = "audio/x-raw\,\ layout\=\(string\)interleaved\,\ rate\=\(int\)44100\,\ format\=\(string\)F32LE\,\ channels\=\(int\)1"
/GstPipeline:pipeline0/avenc_aac:avenc_aac0.GstPad:sink: caps = "audio/x-raw\,\ layout\=\(string\)interleaved\,\ rate\=\(int\)44100\,\ format\=\(string\)F32LE\,\ channels\=\(int\)1"
/GstPipeline:pipeline0/GstAudioResample:audioresample0.GstPad:sink: caps = "audio/x-raw\,\ layout\=\(string\)interleaved\,\ rate\=\(int\)44100\,\ format\=\(string\)F32LE\,\ channels\=\(int\)1"
/GstPipeline:pipeline0/GstAudioConvert:audioconvert0.GstPad:sink: caps = "audio/x-raw\,\ format\=\(string\)S16LE\,\ layout\=\(string\)interleaved\,\ rate\=\(int\)44100\,\ channels\=\(int\)1"
ERROR: from element /GstPipeline:pipeline0/avenc_aac:avenc_aac0: Codec is experimental, but settings don't allow encoders to produce output of experimental quality
Additional debug info:
gstavaudenc.c(335): gst_ffmpegaudenc_set_format (): /GstPipeline:pipeline0/avenc_aac:avenc_aac0:
This codec may not create output that is conformant to the specs or of good quality. If you must use it anyway, set the compliance property to experimental
EOS on shutdown enabled -- waiting for EOS after Error
Waiting for EOS...
ERROR: from element /GstPipeline:pipeline0/avenc_aac:avenc_aac0: GStreamer error: negotiation problem.
Additional debug info:
gstaudioencoder.c(1225): gst_audio_encoder_chain (): /GstPipeline:pipeline0/avenc_aac:avenc_aac0:
encoder not initialized
ERROR: from element /GstPipeline:pipeline0/GstAlsaSrc:alsasrc0: Internal data flow error.
Additional debug info:
gstbasesrc.c(2933): gst_base_src_loop (): /GstPipeline:pipeline0/GstAlsaSrc:alsasrc0:
streaming task paused, reason not-negotiated (-4)
/GstPipeline:pipeline0/GstV4l2Src:v4l2src0.GstPad:src: caps = "video/x-raw\,\ format\=\(string\)I420\,\ width\=\(int\)1280\,\ height\=\(int\)720\,\ pixel-aspect-ratio\=\(fraction\)1/1\,\ interlace-mode\=\(string\)progressive\,\ framerate\=\(fraction\)30/1"
/GstPipeline:pipeline0/GstCapsFilter:mycapsfilter.GstPad:src: caps = "video/x-raw\,\ format\=\(string\)I420\,\ width\=\(int\)1280\,\ height\=\(int\)720\,\ pixel-aspect-ratio\=\(fraction\)1/1\,\ interlace-mode\=\(string\)progressive\,\ framerate\=\(fraction\)30/1"
/GstPipeline:pipeline0/GstX264Enc:x264enc0.GstPad:sink: caps = "video/x-raw\,\ format\=\(string\)I420\,\ width\=\(int\)1280\,\ height\=\(int\)720\,\ pixel-aspect-ratio\=\(fraction\)1/1\,\ interlace-mode\=\(string\)progressive\,\ framerate\=\(fraction\)30/1"
/GstPipeline:pipeline0/GstCapsFilter:mycapsfilter.GstPad:sink: caps = "video/x-raw\,\ format\=\(string\)I420\,\ width\=\(int\)1280\,\ height\=\(int\)720\,\ pixel-aspect-ratio\=\(fraction\)1/1\,\ interlace-mode\=\(string\)progressive\,\ framerate\=\(fraction\)30/1"
Redistribute latency...
/GstPipeline:pipeline0/GstX264Enc:x264enc0.GstPad:src: caps = "video/x-h264\,\ codec_data\=\(buffer\)0164001fffe100186764001facb200a00b760220000003002000000791e3064901000568ebccb22c\,\ stream-format\=\(string\)avc\,\ alignment\=\(string\)au\,\ level\=\(string\)3.1\,\ profile\=\(string\)high\,\ width\=\(int\)1280\,\ height\=\(int\)720\,\ pixel-aspect-ratio\=\(fraction\)1/1\,\ framerate\=\(fraction\)30/1"
/GstPipeline:pipeline0/GstQueue:queue0.GstPad:src: caps = "video/x-h264\,\ codec_data\=\(buffer\)0164001fffe100186764001facb200a00b760220000003002000000791e3064901000568ebccb22c\,\ stream-format\=\(string\)avc\,\ alignment\=\(string\)au\,\ level\=\(string\)3.1\,\ profile\=\(string\)high\,\ width\=\(int\)1280\,\ height\=\(int\)720\,\ pixel-aspect-ratio\=\(fraction\)1/1\,\ framerate\=\(fraction\)30/1"
/GstPipeline:pipeline0/GstMP4Mux:m.GstPad:video_0: caps = "video/x-h264\,\ codec_data\=\(buffer\)0164001fffe100186764001facb200a00b760220000003002000000791e3064901000568ebccb22c\,\ stream-format\=\(string\)avc\,\ alignment\=\(string\)au\,\ level\=\(string\)3.1\,\ profile\=\(string\)high\,\ width\=\(int\)1280\,\ height\=\(int\)720\,\ pixel-aspect-ratio\=\(fraction\)1/1\,\ framerate\=\(fraction\)30/1"
/GstPipeline:pipeline0/GstQueue:queue0.GstPad:sink: caps = "video/x-h264\,\ codec_data\=\(buffer\)0164001fffe100186764001facb200a00b760220000003002000000791e3064901000568ebccb22c\,\ stream-format\=\(string\)avc\,\ alignment\=\(string\)au\,\ level\=\(string\)3.1\,\ profile\=\(string\)high\,\ width\=\(int\)1280\,\ height\=\(int\)720\,\ pixel-aspect-ratio\=\(fraction\)1/1\,\ framerate\=\(fraction\)30/1"
/GstPipeline:pipeline0/GstMP4Mux:m.GstPad:src: caps = "video/quicktime\,\ variant\=\(string\)iso"
/GstPipeline:pipeline0/GstFileSink:filesink0.GstPad:sink: caps = "video/quicktime\,\ variant\=\(string\)iso"