Re: [FFmpeg-devel] [PATCH 1/2] avformat/demux: use io_close2 when closing avfromat

[Andreas Rheinhardt <andreas.rheinhardt@outlook.com>]

Andreas Rheinhardt:
> Kacper Michajłow:
>> It's not valid to call avio_close() on context that has not been open
>> with avio_open().
>>
>> This fixes use of custom IO. (io_open / io_close2 callbacks)
>>
>> Note that by default io_close2 is set to io_close2_default() which calls
>> avio_close(), so default case will work the same as before.
>>
>> Signed-off-by: Kacper Michajłow <kasper93@gmail.com>
>> ---
>>  libavformat/demux.c | 3 +--
>>  1 file changed, 1 insertion(+), 2 deletions(-)
>>
>> diff --git a/libavformat/demux.c b/libavformat/demux.c
>> index 2795863567..ecd4f40da9 100644
>> --- a/libavformat/demux.c
>> +++ b/libavformat/demux.c
>> @@ -383,11 +383,10 @@ void avformat_close_input(AVFormatContext **ps)
>>          if (ffifmt(s->iformat)->read_close)
>>              ffifmt(s->iformat)->read_close(s);
>>  
>> +    ff_format_io_close(s, &pb);
>>      avformat_free_context(s);
>>  
>>      *ps = NULL;
>> -
>> -    avio_close(pb);
>>  }
>>  
>>  static void force_codec_ids(AVFormatContext *s, AVStream *st)
> 
> avformat_open_input() sets AVFMT_FLAG_CUSTOM_IO when using custom IO and
> avformat_close_input() checks for this and does not free the
> AVFormatContext's AVIOContext in this case (but does avio_close(NULL) in
> this case).
> Your patch furthermore presumes that the custom IO context is compatible
> with io_close2, which need not be true at all (one can use custom IO
> without ever touching io_open/io_close2 pointers; I expect users that
> use custom IO, but not formats that open new AVIOContexts to do so).

On reading a bit further, init_input() uses io_open to open the
AVIOContext in case no AVIOContext was supplied (and one is needed).
This means that the AVFMT_FLAG_CUSTOM_IO flag is misleading, as it is
possible to use custom IO even with this flag unset. It also means that
your patch is likely correct.

- Andreas

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