[Ffmpeg-devel] MPEG2 seeking broken

Tue Mar 7 11:32:47 CET 2006

Hi everyone,

As a follow-up to the email I sent a few days ago, I tried ffplay
(latest from CVS) on Linux on chems1.vob. The default seeking mode of
ffplay works. 

But it's not "precise" enough for me (seeking 10s away is too far for
what we are using to analyse video frames). So I added the value set by
our application to seek inside any file. Namely I replaced :

ret = av_seek_frame(is->ic, -1, is->seek_pos, is->seek_flags);
=>
ret = av_seek_frame(is->ic, 0, 152393, AVSEEK_FLAG_BACKWARD);

and also tried :

ret = av_seek_frame(is->ic, -1, is->seek_pos, is->seek_flags);
=>
ret = av_seek_frame(is->ic, 1, 152393, AVSEEK_FLAG_BACKWARD);

All these values are legitimate (AFAIK). There are 2 streams (1 video
and 1 audio) and we seek at around 1.6s from the first frame. The
BACKWARD flag is to ensure we go to the previous keyframe and not the
next one (otherwise we might miss a lot of content on files like small
AVIs).

Both case crash exactly like the MSVC debug build we use. I attach the
backtrace of gdb in both cases.

Setting the stream index to -1 doesn't crash. But I'm not sure it would
be clean for some formats where it would seek at an audio location and
in the middle of P/B frames.

This crash doesn't occur with a version of libavcodec/mpeg12.c from
2006-03-01.

Steve
-------------- next part --------------
ret = av_seek_frame(is->ic, -1, is->seek_pos, is->seek_flags);
=>
ret = av_seek_frame(is->ic, 1, 152393, AVSEEK_FLAG_BACKWARD);

(gdb) backtrace
#0  0x080bb7d4 in MPV_motion (s=0x83e3080,
    dest_y=0x84ddf70 "\020\021\020\017\021\023\020\016\020\020\017\022\021\022\020\023\0203\uffff\uffff\uffff\uffff\uffff\uffff\uffff\uffff\uffff\uffff\uffff\uffff\uffff\uffff\uffff\uffff\uffff\uffff\uffff\uffff\uffff\uffff\uffff\uffff\uffff\uffff\uffff\uffff\uffff\uffff\uffff\uffff\uffff\uffff\uffff\uffff\uffff\uffff\uffff\uffff\uffff\uffff\uffff\uffff\uffff\uffff\uffff\uffff\uffff\uffff\uffff\uffff\uffff\uffff\uffff\uffff\uffff\uffff\uffff\uffff\uffff\uffff\uffff\uffff\uffff\uffff\uffff\uffff\uffff\uffff\uffff\uffff\uffff\uffff\uffff\uffff\uffff\uffff\uffff\uffff\uffff\uffff\uffff\uffff\uffff\uffff\uffff\uffff\uffff\uffff\uffff\uffff\uffff\uffff\uffff\uffff\uffff\uffff\uffff\uffff\uffff\uffff\uffff\uffff\uffff\uffff\uffff\uffff\uffff\uffff\uffff\uffff\uffff\uffff\uffff\uffff\uffff\uffff\uffff\uffff\uffff\uffff\uffff\uffff\uffff\uffff\uffff\uffff\uffff\uffff\uffff\uffff\uffff\uffff\uffff\uffff\uffff\uffff\uffff\uffff\uffff\uffff\uffff\uffff\uffff\uffff\uffff\uffff\uffff\uffff\uffff\uffff\uffff?\uffff\uffff\uffff\uffff\uffff\uffff\uffff\uffff\uffff\uffff\uffff\uffff\uffff\uffff\uffff\uffff\uffff\uffff\uffff\uffff\uffff\uffff\uffff\uffff\uffff\uffff\uffff"..., dest_cb=Variable "dest_cb" is not available.
)
    at mpegvideo.c:2938
#1  0x080c2221 in MPV_decode_mb (s=0x83e3080, block=0x867c000) at mpegvideo.c:3919
#2  0x0816eb81 in mpeg_decode_slice (s1=0x83e3080, mb_y=2, buf=0xb625a304, buf_size=48128) at mpeg12.c:2609
#3  0x08171177 in mpeg_decode_frame (avctx=0x83df2c0, data=0x8644e60, data_size=0xb625a404,
    buf=0x83e5950 "'\"@)8\bA\uffff\uffff\uffff\u04f6\231\225\u047a\236\002\uffff0\rng\u0130\uffff\uffff\uffff\u04e7\uffff\234\ad\006a\uffff\uffff\\\233\uffff\uffff)-\002\021\uffff\220\uffff7\020@\a\uffff\223![\237\uffff\020Z\022\204\uffff\uffff?\032\uffff2\uffff[}\uffffi\uffff\b6\u0174D\uffff\uffff:\220\217\u05a0\037\uffff0#\207\uffff'\uffff\222\uffff=\uffff\uffffG\003{\uffff$\234\uffffH\026\rG\n\206\uffff\202\uffff8\uffff\025$\016X1", buf_size=11590) at mpeg12.c:3157
#4  0x080ac815 in avcodec_decode_video (avctx=0x83df2c0, picture=0x8644e60, got_picture_ptr=0xb625a404,
    buf=0x83e5950 "'\"@)8\bA\uffff\uffff\uffff\u04f6\231\225\u047a\236\002\uffff0\rng\u0130\uffff\uffff\uffff\u04e7\uffff\234\ad\006a\uffff\uffff\\\233\uffff\uffff)-\002\021\uffff\220\uffff7\020@\a\uffff\223![\237\uffff\020Z\022\204\uffff\uffff?\032\uffff2\uffff[}\uffffi\uffff\b6\u0174D\uffff\uffff:\220\217\u05a0\037\uffff0#\207\uffff'\uffff\222\uffff=\uffff\uffffG\003{\uffff$\234\uffffH\026\rG\n\206\uffff\202\uffff8\uffff\025$\016X1", buf_size=11590) at utils.c:943
#5  0x08058005 in video_thread (arg=0xb725d020) at ffplay.c:1283
#6  0xb7e92591 in SDL_RunThread () from /usr/lib/libSDL-1.2.so.0
#7  0xb7e92861 in SDL_KillThread () from /usr/lib/libSDL-1.2.so.0
#8  0xb7e2f361 in start_thread () from /lib/tls/i686/cmov/libpthread.so.0
#9  0xb7dc4bde in clone () from /lib/tls/i686/cmov/libc.so.6

ret = av_seek_frame(is->ic, -1, is->seek_pos, is->seek_flags);
=>
ret = av_seek_frame(is->ic, 0, 152393, AVSEEK_FLAG_BACKWARD);

(gdb) backtrace
#0  0x080bb7d4 in MPV_motion (s=0x83e3080,
    dest_y=0x85361b0 "31122213466779:;:999:99978788888766431101-+,/00../0/-,,+(*+-./.--./1223333210.,-/+++,,,.,,---..-+,,+,-/0000013454755664554432446686669988:888987875578867899:;;;:866852244753574133442101320/.,,,,+-.-,."..., dest_cb=Variable "dest_cb" is not available.
) at mpegvideo.c:2938
#1  0x080c2221 in MPV_decode_mb (s=0x83e3080, block=0x867c070) at mpegvideo.c:3919
#2  0x0816eb81 in mpeg_decode_slice (s1=0x83e3080, mb_y=17, buf=0xb6273304, buf_size=409088) at mpeg12.c:2609
#3  0x08171177 in mpeg_decode_frame (avctx=0x83df2c0, data=0x8644f10, data_size=0xb6273404,
    buf=0x83e5110 "\004\uffffy\uffff\uffff\uffffvt\uffff\uffff\uffff$pemp\uffff\226\217>\226\u06b9\uffff\034\uffff\205\u01a6\u05b5\uffff\uffff#\0274\uffff\212-z.\214\uffff\uffffb\030\uffff \uffff\034\uffff\205\uffffQ\uffff\uffff\uffffX\uffff\u0536\217\227Z\uffff\uffffF\uffff\025\uffff\ufffff\uffff\uffff\215\004\uffff!\uffff\225\uffff\230[{'\2077\027C\233|-\uffff\uffff\uffff\uffff\002\uffff\uffff5\uffff\037>\\\234\uffff\uffffV\207\uffff\230\200\uffff4YJ\035\0245\uffff\u01b4\uffff\232\217\uffff\206\"J\uffff\005H\030\uffffMdo\akk#G\uffff\005I[\uffff\uffffm\uffff\uffffh\uffff+e\uffffg\221Z?s\uffff#\233\uffffd\215k\uffff\234\uffff\uffffmq\uffff\005\uffffh\035#Z!\206x\uffff\"\223'Sl\fg\227\023\006\215\uffff\uffff\uffff3"..., buf_size=1773) at mpeg12.c:3157
#4  0x080ac815 in avcodec_decode_video (avctx=0x83df2c0, picture=0x8644f10, got_picture_ptr=0xb6273404,
    buf=0x83e5110 "\004\uffffy\uffff\uffff\uffffvt\uffff\uffff\uffff$pemp\uffff\226\217>\226\u06b9\uffff\034\uffff\205\u01a6\u05b5\uffff\uffff#\0274\uffff\212-z.\214\uffff\uffffb\030\uffff \uffff\034\uffff\205\uffffQ\uffff\uffff\uffffX\uffff\u0536\217\227Z\uffff\uffffF\uffff\025\uffff\ufffff\uffff\uffff\215\004\uffff!\uffff\225\uffff\230[{'\2077\027C\233|-\uffff\uffff\uffff\uffff\002\uffff\uffff5\uffff\037>\\\234\uffff\uffffV\207\uffff\230\200\uffff4YJ\035\0245\uffff\u01b4\uffff\232\217\uffff\206\"J\uffff\005H\030\uffffMdo\akk#G\uffff\005I[\uffff\uffffm\uffff\uffffh\uffff+e\uffffg\221Z?s\uffff#\233\uffffd\215k\uffff\234\uffff\uffffmq\uffff\005\uffffh\035#Z!\206x\uffff\"\223'Sl\fg\227\023\006\215\uffff\uffff\uffff3"..., buf_size=1773) at utils.c:943
#5  0x08058005 in video_thread (arg=0xb7276020) at ffplay.c:1283
#6  0xb7eab591 in SDL_RunThread () from /usr/lib/libSDL-1.2.so.0
#7  0xb7eab861 in SDL_KillThread () from /usr/lib/libSDL-1.2.so.0
#8  0xb7e48361 in start_thread () from /lib/tls/i686/cmov/libpthread.so.0
#9  0xb7dddbde in clone () from /lib/tls/i686/cmov/libc.so.6

-1 for stream number works