On Fri, 2 Dec 2022, Gyan Doshi wrote:
On 2022-12-02 06:16 am, Chris Ribble wrote:
On Thu, Dec 1, 2022 at 4:51 PM Marton Balint <c...@passwd.hu> wrote:
Can you explain why those files are considered valid, or why it makes
sense to generate such files?
Thanks,
Marton
As far as I can tell, the file that a user provided with this problem
was generated by an encoder (running FFmpeg 3.4) that started writing
zero-sized samples when their video switcher + capture card stopped
receiving audio input. I'm not arguing that it's good for files to be
generated like this, but it's nice for FFmpeg to be able to process
them all the same (i.e. the robustness principle).
With this patch reverted, FFmpeg can accept an input file that is
partially broken (with playback anomalies due to the presence of
zero-sized samples) and produce a valid, working output mp4 (or DASH
stream), just like it could in release 5.0 and older.
One of the best things about FFmpeg is that it can fix invalid
container metadata. I feel like losing that capability for this
scenario is a regression.
FWIW, we don't discard regular MP4s with sample entries of 0 in stts, which
is only permitted for the last solo sample in a track. So, I agree.
More strict enforcement of sample size was introduced to avoid DOS/Timeout
with crafted (fuzzed) files and disallow emitting zero sized packets.
Invalid file support is not something that is always worth doing, there
are other, more important factors, like limiting code complexity or
improving resiliance against denial of service. The problem here is that I
honestly don't know if a zero sample size is against spec, just stupid, or
there is a legitimate use for it.
So I sent a 2 patch series which fixes the original issue differently.
Please test and review them if you can.
Thanks,
Marton
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