SIGSEGV from libavformat/movenc.c

[Suhwan]

Summary of the bug:
There is SIGSEGV from libavformat/movenc.c

libavformat/movenc.c:3101:47: runtime error: member access within null pointer of type 'AVFormatContext' (aka 'struct AVFormatContext')

Program received signal SIGSEGV, Segmentation fault.
0x00000000016c14aa in mov_write_udta_sdp (pb=<optimized out>, track=<optimized out>)
    at libavformat/movenc.c:3101
3101	    ff_sdp_write_media(buf, sizeof(buf), ctx->streams[0], track->src_track,
(gdb) bt
#0  0x00000000016c14aa in mov_write_udta_sdp (pb=<optimized out>, track=<optimized out>)
    at libavformat/movenc.c:3101
#1  mov_write_trak_tag (s=0x90cac40, pb=0x90ffe80, mov=0x9104880, track=<optimized out>, st=0x9104d00)
    at libavformat/movenc.c:3192
#2  0x00000000016bb656 in mov_write_moov_tag (pb=<optimized out>, mov=0x9104880, s=0x90cac40)
    at libavformat/movenc.c:4012
#3  0x00000000016a7de4 in mov_write_trailer (s=0x90cac40) at libavformat/movenc.c:6773
#4  0x0000000001791e94 in av_write_trailer (s=<optimized out>) at libavformat/mux.c:1283
#5  0x000000000048ff9c in transcode () at fftools/ffmpeg.c:4726
#6  0x0000000000487de4 in main (argc=27, argv=<optimized out>) at fftools/ffmpeg.c:4894

How to reproduce:

% ./ffmpeg_g -stream_loop 1 -y -r 55 -i xtrem-sport.mp4 -loglevel 40 -map 0 -c copy -c:s:0 aptx_hd -aframes 20 -ab 636k -ar 48000 -b:v 388k -strict 1 tmp.mov

ffmpeg version N-94969-gc2ab998ff3 Copyright (c) 2000-2019 the FFmpeg developers
  built with clang version 6.0.0-1ubuntu2 (tags/RELEASE_600/final)
  configuration: --cc=clang --cxx=clang++ --ld=clang --enable-debug --toolchain=clang-usan

[Suhwan]

poc

[mkver]

Fixed in 22c3cd176079dd104ec7610ead697235b04396f1.