rtpL16depay, rtpL24depay: support depayloading in place

Submitted by Petr Kulhavy

Description

It seems that rtpL16depay, rtpL24depay (and I guess also other rtp-depay functions) are failing to depayload in place. It always allocates a new buffer and copies the payload.

This is the log I'm seeing:

0:00:13.489419481 1060 0x1ec5150 DEBUG rtpL16depay gstrtpL16depay.c:243:gst_rtp_L16_depay_process:`<rtpl16depay0>` got payload of 192 bytes
0:00:13.489596481 1060 0x1ec5150 LOG GST_BUFFER gstbuffer.c:798:gst_buffer_new: new 0x75c05370
0:00:13.489760981 1060 0x1ec5150 LOG GST_BUFFER gstbuffer.c:2038:gst_buffer_copy_region: new region copy 0x75c05370 of 0x75c054b0 12-192
0:00:13.490969772 1060 0x1ec5150 LOG GST_BUFFER gstbuffer.c:514:gst_buffer_copy_into: copy 0x75c054b0 to 0x75c05370, offset 12-192/204

0:00:13.493352979 1060 0x1ec5150 TRACE GST_LOCKING gstminiobject.c:177:gst_mini_object_lock: lock 0x1ecb690: state 00020000, access_mode 3
0:00:13.493546312 1060 0x1ec5150 DEBUG GST_LOCKING gstminiobject.c:212:gst_mini_object_lock: lock failed 0x1ecb690: state 00020000, access_mode 3
0:00:13.493717020 1060 0x1ec5150 DEBUG GST_MEMORY gstmemory.c:317:gst_memory_map: mem 0x1ecb690: lock 3 failed
0:00:13.493910270 1060 0x1ec5150 TRACE GST_REFCOUNTING gstobject.c:249:gst_object_ref:<allocatorsysmem0> 0x1ddc010 ref 6->7
0:00:13.494091270 1060 0x1ec5150 DEBUG GST_MEMORY gstmemory.c:138:gst_memory_init: new memory 0x1ecb578, maxsize:195 offset:0 size:192
0:00:13.494364978 1060 0x1ec5150 DEBUG GST_PERFORMANCE gstallocator.c:462:_sysmem_copy: memcpy 192 memory 0x1ecb690 -> 0x1ecb578

And this is the command:
GST_DEBUG=9 gst-launch-1.0 audiotestsrc is-live=true wave=silence samplesperbuffer=48 ! "audio/x-raw,format=(string)S16BE,rate=(int)48000,channels=(int)2,channel-mask=(int)0x3" ! rtpL16pay ! rtpL16depay ! fakesink
2>&1 | grep -B 5 copy

It happens in gst_audio_buffer_reorder_channels() when mapping the buffer read-write. It doesn't really matter what the source is, the same happens with udpsrc.

The other thing here is that if the channels don't require reordering (like in my case) the buffer shouldn't be remapped read-write. Otherwise the potential buffer copy is redundant.