Here's gdb's back trace of the seg fault, but with debugging symbols for libavcodec57.
-- Time is the fire in which we all burn.
#0 move_audio (sf_size=<optimized out>, venc=0x9e40ddc0) at src/libavcodec/vorbisenc.c:1073 save = <optimized out> input = <optimized out> len = <optimized out> cur = 0x0 frame_size = <optimized out> subframes = <optimized out> sf = 0 ch = 0 #1 vorbis_encode_frame (avctx=0x9e40d380, avpkt=0x9ed9ce94, frame=0x9e4708a0, got_packet_ptr=0x9ed9ce88) at src/libavcodec/vorbisenc.c:1124 venc = 0x9e40ddc0 i = <optimized out> ret = <optimized out> frame_size = 1024 mode = <optimized out> mapping = <optimized out> pb = {bit_buf = 0, bit_left = -1208666538, buf = 0x4 <error: Cannot access memory at address 0x4>, buf_ptr = 0xb7f53c8c <mlt_properties_get_data+316> "\203\304\020\203\304\034\061\300[^_]Í\264&", buf_end = 0x80000000 "\177ELF\001\001\001", size_in_bits = 0} #2 0xabd8ffa4 in avcodec_encode_audio2 (avctx=<optimized out>, avpkt=<optimized out>, frame=0x9e4708a0, got_packet_ptr=<optimized out>) at src/libavcodec/encode.c:198 extended_frame = <optimized out> padded_frame = 0x0 ret = <optimized out> user_pkt = <optimized out> needs_realloc = <optimized out> #3 0xb2005f23 in consumer_thread (arg=0x80770710) at consumer_avformat.c:1622 p = 0x912a6030 got_packet = 0 ret = <optimized out> stream = 0x9e40d0a0 codec = 0x9e40d380 pkt = {buf = 0x0, pts = -9223372036854775808, dts = -9223372036854775808, data = 0x9e400480 "", size = 43008, stream_index = 0, flags = 0, side_data = 0x0, side_data_elems = 0, duration = 0, pos = -1, convergence_duration = 0} j = 0 n = <optimized out> consumer = 0x80770710 properties = 0x80770710 terminate_on_pause = 1 terminated = 0 real_time_output = -1 ante = {tv_sec = 1514957417, tv_usec = 124160} fps = 25 width = 1920 height = 1080 img_width = 1920 img_height = 1080 channels = 2 total_channels = 2 frequency = 48000 pcm = 0x950298e0 samples = 64 audio_outbuf = 0x9e400480 "" audio_input_nb_samples = 64 frame_count = 1 video_outbuf = 0x9a3ff020 "P\222\r\235\001*\200\a8\004" frame = 0x0 frame_properties = <optimized out> queue = 0x8076ecd0 fifo = 0x9e40bb88 image = 0x925f8030 "\020\200\020\200\020\200\020\200\020\200\020\200\020\200\020\200\020\200\020\200\020\200\020\200\020\200\020\200\020\200\020\200\020\200\020\200\020\200\020\200\020\200\020\200\020\200\020\200\020\200\020\200\020\200\020\200\020\200\020\200\020\200\020\200\020\200\020\200\020\200\020\200\020\200\020\200\020\200\020\200\020\200\020\200\020\200\020\200\020\200\020\200\020\200\020\200\020\200\020\200\020\200\020\200\020\200\020\200\020\200\020\200\020\200\020\200\020\200\020\200\020\200\020\200\020\200\020\200\020\200\020\200\020\200\020\200\020\200\020\200\020\200\020\200\020\200\020\200\020\200\020\200\020\200\020\200\020\200\020\200\020\200\020\200\020\200\020\200\020\200\020\200\020\200\020\200\020\200\020\200\020\200\020\200\020\200\020\200\020\200\020\200\020\200\020\200\020\200\020\200"... img_fmt = mlt_image_yuv422 converted_avframe = <optimized out> audio_avframe = 0x9e4708a0 video_avframe = 0x9e40cf00 audio_buf_1 = 0x9a343020 "" audio_buf_2 = 0x0 count = 1 oc = 0x9e40b080 video_st = 0x9e40bc60 audio_st = {0x9e40d0a0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0} audio_pts = 0.02 video_pts = 0.040000000000000001 frames = 1 total_time = 39562 fmt = 0xabb53c40 <ff_webm_muxer> filename = 0x9e40acd8 "/home/kingsley/tmp/test.webm" format = <optimized out> vcodec = <optimized out> acodec = <optimized out> audio_codec = <optimized out> video_codec = <optimized out> audio_codec_id = 86021 video_codec_id = <optimized out> key = "channels.7", '\000' <repeats 16 times> frame_meta_properties = 0x9e40ad00 error_count = 0 sample_count = {1024, 0, 0, 0, 0, 0, 0, 0} header_written = 1 i = 0 aud_fmt = mlt_audio_f32le sample_bytes = 4 #4 0xb7f2c32d in start_thread (arg=0x9ed9db40) at pthread_create.c:456 __res = <optimized out> pd = 0x9ed9db40 now = <optimized out> unwind_buf = {cancel_jmp_buf = {{jmp_buf = {-1208741888, -1629889728, -1629889728, -1629891544, 435968905, 1340044251}, mask_was_saved = 0}}, priv = {pad = {0x0, 0x0, 0x0, 0x0}, data = {prev = 0x0, cleanup = 0x0, canceltype = 0}}} not_first_call = 0 #5 0xb7e54616 in clone () at ../sysdeps/unix/sysv/linux/i386/clone.S:110 No locals.