Endless loop with ffmpeg 5.0 and vapoursynth R57-2

[lighterowl]

Opening any d2v file (generated with either dgindex or d2vwitch) causes vspipe/vsedit to go into an endless loop. Just calling d2v.Source is enough to trigger this :

import vapoursynth as vs
src = vs.core.d2v.Source('/tmp/foobar/VIDEO_TS/VTS_01_1.d2v')

Breaking a running vspipe under gdb causes a stop in the exact same location :

Thread 1 (Thread 0x7ffff767e5c0 (LWP 11527) "vspipe"):
#0  0x00007ffff7c301ec in read () at /usr/lib/libc.so.6
#1  0x00007ffff7bb32d8 in __GI__IO_file_xsgetn () at /usr/lib/libc.so.6
#2  0x00007ffff7ba82f9 in fread () at /usr/lib/libc.so.6
#3  0x00007fffe2d92ab6 in fread (__stream=<optimized out>, __n=32768, __size=1, __ptr=0x555555863180) at /usr/include/bits/stdio2.h:293
#4  read_packet(void*, uint8_t*, int) (opaque=0x5555557de420, buf=0x555555863180 "6\215\032\064a\206ѣF\214\060\332\064hц\033F\215\032\060\303hѣF\030m\032\064h\303\r\243F\215\030a\264hѣ\f6\215\032\064a\206ѣF\214\060\300", size=32768) at ../d2vsource/src/core/decode.cpp:113
#5  0x00007ffff236a879 in avio_r8 () at /usr/lib/libavformat.so.59
#6  0x00007ffff242bcf6 in  () at /usr/lib/libavformat.so.59
#7  0x00007ffff242c88c in  () at /usr/lib/libavformat.so.59
#8  0x00007ffff238fbe6 in  () at /usr/lib/libavformat.so.59
#9  0x00007ffff2392cdb in avformat_find_stream_info () at /usr/lib/libavformat.so.59
#10 0x00007fffe2d9347d in decodeframe(int, d2vcontext*, decodecontext*, AVFrame*, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >&) (frame_num=frame_num@entry=0, ctx=0x5555557de070, dctx=0x5555557de420, out=<optimized out>, err="") at ../d2vsource/src/core/decode.cpp:406

Running d2vsource from newffmpeg branch.