VLC for iOS crashes playing video

Oops, I mean "nightline10_29_2013.mpg"

I attached the file via the separate attachment page (if you try to attach when writing up a bug, it says limited to 500K, and IIRC, it doesn't give a progress bar for feedback).

Note, this happens at normal playback speed too (my main intended use for VLC is to play various news/documentary/reality shows faster than realtime).

assigned to @fkuehne

added Component::Port: iOS Platform::iOS labels

Known issue in the mp2v decoder included in both libav and ffmpeg and it's still not fixed since 8 months despite reported repeatedly.

(lldb) bt
* thread [#44](https://code.videolan.org/videolan/vlc/-/issues/44): tid = 0x592249, 0x00326920 VLC for iOS`mpeg_decode_slice [inlined] mpeg2_fast_decode_block_non_intra + 461 at mpeg12dec.c:453, stop reason = EXC_BAD_ACCESS (code=1, address=0x1240601b)
  * frame [#0](https://code.videolan.org/videolan/vlc/-/issues/0): 0x00326920 VLC for iOS`mpeg_decode_slice [inlined] mpeg2_fast_decode_block_non_intra + 461 at mpeg12dec.c:453
    frame [#1](https://code.videolan.org/videolan/vlc/-/issues/1): 0x00326753 VLC for iOS`mpeg_decode_slice [inlined] mpeg_decode_mb + 5712 at mpeg12dec.c:981
    frame [#2](https://code.videolan.org/videolan/vlc/-/issues/2): 0x00325103 VLC for iOS`mpeg_decode_slice(s=0x0f2b4000, mb_y=<unavailable>, buf=<unavailable>, buf_size=<unavailable>) + 1699 at mpeg12dec.c:1690
    frame [#3](https://code.videolan.org/videolan/vlc/-/issues/3): 0x0032422e VLC for iOS`decode_chunks(avctx=0x0f208c00, picture=0x1a86d580, got_output=<unavailable>, buf=<unavailable>, buf_size=<unavailable>) + 9934 at mpeg12dec.c:2422
    frame [#4](https://code.videolan.org/videolan/vlc/-/issues/4): 0x00321af5 VLC for iOS`mpeg_decode_frame(avctx=<unavailable>, data=<unavailable>, got_output=<unavailable>, avpkt=0xb05ffe20) + 741 at mpeg12dec.c:2484
    frame [#5](https://code.videolan.org/videolan/vlc/-/issues/5): 0x003b4e12 VLC for iOS`avcodec_decode_video2 + 258
    frame [#6](https://code.videolan.org/videolan/vlc/-/issues/6): 0x008f222e VLC for iOS`DecodeVideo(p_dec=0x0f20e874, pp_block=<unavailable>) + 1038 at video.c:607
    frame [#7](https://code.videolan.org/videolan/vlc/-/issues/7): 0x008888d2 VLC for iOS`DecoderDecodeVideo(p_dec=0x0f20e874, p_block=0x0e3b4200) + 50 at decoder.c:1375
    frame [#8](https://code.videolan.org/videolan/vlc/-/issues/8): 0x008884e1 VLC for iOS`DecoderThread [inlined] DecoderProcessVideo(p_block=0x0e853c40, p_block=0x0e853c40, p_block=0x0e853c40, p_block=0x0e853c40, p_block=0x0e853c40) + 158 at decoder.c:1580
    frame [#9](https://code.videolan.org/videolan/vlc/-/issues/9): 0x00888443 VLC for iOS`DecoderThread [inlined] DecoderProcess(p_block=<unavailable>) + 1591 at decoder.c:1775
    frame [#10](https://code.videolan.org/videolan/vlc/-/issues/10): 0x00887e0c VLC for iOS`DecoderThread(p_data=0x0f20e874) + 316 at decoder.c:906
    frame [#11](https://code.videolan.org/videolan/vlc/-/issues/11): 0x059545b7 libsystem_c.dylib`_pthread_start + 344
(lldb)

added Status::not VLC label

changed milestone to %iOS 2.2.1

closed

Replying to [comment:5 fkuehne]:

Known issue in the mp2v decoder included in both libav and ffmpeg and it's still not fixed since 8 months despite reported repeatedly.

Sorry, it appears we forgot about the issue: Could you point me to the reports?

{{{ (lldb) bt

thread #44 (closed): tid = 0x592249, 0x00326920 VLC for iOS`mpeg_decode_slice [inlined] mpeg2_fast_decode_block_non_intra + 461 at mpeg12dec.c:453, stop reason = EXC_BAD_ACCESS (code=1, address=0x1240601b) }}}

Thank you for the backtrace, I didn't know if my guess from ticket #9713 (closed) was correct or not (and I couldn't test)! Please note that even with the current fixes, CODEC_FLAG2_FAST may still crash for invalid input streams, so I strongly suggest not to enable it by default (no matter the platform).

It's fixed in both libav and FFmpeg using different approaches now.

Thanks for coming back to me. Disabling CODEC_FLAG2_FAST is not an option, sorry, as we need every bit of speed possible on mobile devices and it's probably a good idea to resolve those crashes one by one. Now that we have sufficient crash reporting facilities in place, this will be quite fast.

Replying to [comment:7 fkuehne]:

Thanks for coming back to me. Disabling CODEC_FLAG2_FAST is not an option, sorry, as we need every bit of speed possible on mobile devices and it's probably a good idea to resolve those crashes one by one.

I believe you misunderstand: The fast option avoids some checks to produce faster decoding assuming that the input stream is valid, if these checks are added, the gain (which is very useful for users who know their input) would be lost. In this specific case, Michael found a (faster) work-around but there are cases for which the fast option leads to invalid memory accesses.

Now that we have sufficient crash reporting facilities in place, this will be quite fast.

These crashes have been reported very, very often in the past, and many patches were sent that were supposed to "fix" them, this is why the code now contains comments to explain the usage of the functions.

To avoid such delays in the future: Could you point me to your original report?

Even with the built in reporting, I think I'll still write up reports here too, so I get some feedback.

If the built in reporting let me sign in and automatically wrote a report I'd get feedback on, great.

I've played a bunch of videos on the newest VLC, and it hasn't crashed playing video on the newest version. Yeah!

Great to hear that! Thanks for the feedback!

VLC for iOS crashes playing video

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