[FFmpeg-devel] [PATCH 1/6] avformat/format: add av_demuxer_find_by_ext

[Gyan Doshi]

On 31-01-2020 10:41 pm, Andreas Rheinhardt wrote:
> Gyan Doshi:
>> Allows selecting demuxer by extension which are more widely recognized
>> by users.
>>
>> Conditional cast added since this function will usually be called after
>> av_find_input_format, and so matches its return type.
> That's not a good point. av_demuxer_find_by_ext() already always
> returns const AVInputFormat *, so you casting the const away when
> returning is pointless. Furthermore, any caller that wants to use this
> new function can simply use a pointer to const AVInputFormat to work
> with both av_find_input_format() and av_demuxer_find_by_ext(). And
> after all, adding const makes the code more future-proof
> (av_find_input_format() will return const AVInputFormat * after the
> next major bump).

Ok, I don't think I should add const to the pointers at the receiving 
end (fftools) since they are global variables and may not be acceptable 
as const. So I'll cast away the const when receiving and remove the 
conditional cast.

Sounds fine?

Gyan

>
>> ---
>>   libavformat/avformat.h |  5 +++++
>>   libavformat/format.c   | 15 +++++++++++++++
>>   libavformat/version.h  |  2 +-
>>   3 files changed, 21 insertions(+), 1 deletion(-)
>>
>> diff --git a/libavformat/avformat.h b/libavformat/avformat.h
>> index 9b9b634ec3..9172ddbc8a 100644
>> --- a/libavformat/avformat.h
>> +++ b/libavformat/avformat.h
>> @@ -2237,6 +2237,11 @@ int avformat_alloc_output_context2(AVFormatContext **ctx, ff_const59 AVOutputFor
>>    */
>>   ff_const59 AVInputFormat *av_find_input_format(const char *short_name);
>>   
>> +/**
>> + * Find AVInputFormat based on an extension.
>> + */
>> +const AVInputFormat *av_demuxer_find_by_ext(const char *extension);
>> +
>>   /**
>>    * Guess the file format.
>>    *
>> diff --git a/libavformat/format.c b/libavformat/format.c
>> index c47490c8eb..9dda6df676 100644
>> --- a/libavformat/format.c
>> +++ b/libavformat/format.c
>> @@ -125,6 +125,21 @@ ff_const59 AVInputFormat *av_find_input_format(const char *short_name)
>>       return NULL;
>>   }
>>   
>> +const AVInputFormat *av_demuxer_find_by_ext(const char *extension)
>> +{
>> +    const AVInputFormat *fmt = NULL;
>> +    void *i = 0;
> Use NULL, it's a pointer after all (yes, I know that
> av_demuxer_iterate() treats it as a uintptr_t internally).
>
>> +    while ((fmt = av_demuxer_iterate(&i)))
>> +        if (fmt->extensions && av_match_name(extension, fmt->extensions))
>> +#if FF_API_AVIOFORMAT
>> +            return (AVInputFormat*)fmt;
>> +#else
>> +            return fmt;
>> +#endif
> As has been said: The first branch of the #if should be deleted (as
> the #if, of course).
>
> - Andreas
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