Following pipeline demonstrates this

gst-launch-1.0.exe audiotestsrc is-live=1 ! audio/x-raw,channels=2,rate=48000 ! avenc_aac ! audio/mpeg,stream-format=raw ! aacparse ! audio/mpeg,stream-format=loas ! fakesink -v

Also, following pipeline fails for LOAS to LOAS(it should have acted as passthrough) but instead tries to convert it to ADTS!! I have also seen it converting to raw from LOAS with one another encoder when it should have acted as passthrough(with a propritery encoder)

gst-launch-1.0.exe audiotestsrc is-live=1 ! audio/x-raw,channels=2,rate=48000 ! avenc_aac ! capssetter caps="audio/mpeg,stream-format=loas" ! aac
parse ! audio/mpeg,stream-format=loas ! fakesink -v
Setting pipeline to PAUSED ...
Pipeline is live and does not need PREROLL ...
/GstPipeline:pipeline0/GstAudioTestSrc:audiotestsrc0.GstPad:src: caps = audio/x-raw, format=(string)F32LE, layout=(string)interleaved, rate=(int)48000, channels=(int)2
/GstPipeline:pipeline0/GstCapsFilter:capsfilter0.GstPad:src: caps = audio/x-raw, format=(string)F32LE, layout=(string)interleaved, rate=(int)48000, channels=(int)2
/GstPipeline:pipeline0/avenc_aac:avenc_aac0.GstPad:sink: caps = audio/x-raw, format=(string)F32LE, layout=(string)interleaved, rate=(int)48000, channels=(int)2
/GstPipeline:pipeline0/GstCapsFilter:capsfilter0.GstPad:sink: caps = audio/x-raw, format=(string)F32LE, layout=(string)interleaved, rate=(int)48000, channels=(int)2
Setting pipeline to PLAYING ...
New clock: GstSystemClock
/GstPipeline:pipeline0/avenc_aac:avenc_aac0.GstPad:src: caps = audio/mpeg, channels=(int)2, rate=(int)48000, mpegversion=(int)4, stream-format=(string)raw, base-profile=(
string)lc, channel-mask=(bitmask)0x0000000000000003, level=(string)2, profile=(string)lc, codec_data=(buffer)119056e500
/GstPipeline:pipeline0/GstCapsSetter:capssetter0.GstPad:src: caps = audio/mpeg, channels=(int)2, rate=(int)48000, mpegversion=(int)4, stream-format=(string)loas, base-pro
file=(string)lc, channel-mask=(bitmask)0x0000000000000003, level=(string)2, profile=(string)lc, codec_data=(buffer)119056e500
/GstPipeline:pipeline0/GstAacParse:aacparse0.GstPad:src: caps = audio/mpeg, channels=(int)2, rate=(int)48000, mpegversion=(int)4, stream-format=(string)adts, base-profile
=(string)lc, channel-mask=(bitmask)0x0000000000000003, level=(string)2, profile=(string)lc, codec_data=(buffer)119056e500, framed=(boolean)true
/GstPipeline:pipeline0/GstAacParse:aacparse0.GstPad:sink: caps = audio/mpeg, channels=(int)2, rate=(int)48000, mpegversion=(int)4, stream-format=(string)loas, base-profil
e=(string)lc, channel-mask=(bitmask)0x0000000000000003, level=(string)2, profile=(string)lc, codec_data=(buffer)119056e500
/GstPipeline:pipeline0/GstCapsSetter:capssetter0.GstPad:sink: caps = audio/mpeg, channels=(int)2, rate=(int)48000, mpegversion=(int)4, stream-format=(string)raw, base-pro
file=(string)lc, channel-mask=(bitmask)0x0000000000000003, level=(string)2, profile=(string)lc, codec_data=(buffer)119056e500
ERROR: from element /GstPipeline:pipeline0/GstAudioTestSrc:audiotestsrc0: Internal data flow error.
Additional debug info:
gstbasesrc.c(2947): gst_base_src_loop (): /GstPipeline:pipeline0/GstAudioTestSrc:audiotestsrc0:
streaming task paused, reason not-negotiated (-4)
Execution ended after 0:00:00.121179642
Setting pipeline to PAUSED ...
Setting pipeline to READY ...
Setting pipeline to NULL ...
Freeing pipeline ...