[FFmpeg-devel] [PATCH v4] avformat/utils: add helper functions to retrieve index entries from an AVStream

[Anton Khirnov]

Quoting James Almer (2021-04-08 15:19:02)
> On 4/8/2021 10:09 AM, Anton Khirnov wrote:
> > Quoting James Almer (2021-04-04 01:12:00)
> >> Signed-off-by: James Almer <jamrial at gmail.com>
> >> ---
> >> Now using the avformat_ prefix as Anton requested. I forgot about it when i
> >> made v3.
> >>
> >>   libavformat/avformat.h | 39 +++++++++++++++++++++++++++++++++++++++
> >>   libavformat/utils.c    | 27 +++++++++++++++++++++++++++
> >>   2 files changed, 66 insertions(+)
> >>
> >> diff --git a/libavformat/avformat.h b/libavformat/avformat.h
> >> index 6a9b09160c..a1e87ef891 100644
> >> --- a/libavformat/avformat.h
> >> +++ b/libavformat/avformat.h
> >> @@ -2767,6 +2767,45 @@ int av_find_default_stream_index(AVFormatContext *s);
> >>    */
> >>   int av_index_search_timestamp(AVStream *st, int64_t timestamp, int flags);
> >>   
> >> +/**
> >> + * Get the index entry count for the given AVStream.
> >> + *
> >> + * @param st stream
> >> + * @return the number of index entries in the stream
> >> + */
> >> +int avformat_index_get_entries_count(AVStream *st);
> >> +
> >> +/**
> >> + * Get the AVIndexEntry corresponding to the given index.
> >> + *
> >> + * @param st          Stream containing the requested AVIndexEntry.
> >> + * @param idx         The desired index.
> >> + * @return A pointer to the requested AVIndexEntry if it exists, NULL otherwise.
> >> + *
> >> + * @note The pointer returned by this function is only guaranteed to be valid
> >> + *       until any function that could alter the stream or the AVFormatContext
> >> + *       that cointains it is called.
> >> + */
> >> +const AVIndexEntry *avformat_index_get_entry(AVStream *st, int idx);
> >> +
> >> +/**
> >> + * Get the AVIndexEntry corresponding to the given timestamp.
> >> + *
> >> + * @param st          Stream containing the requested AVIndexEntry.
> >> + * @param timestamp   Timestamp to retrieve the index entry for.
> >> + * @param flags       If AVSEEK_FLAG_BACKWARD then the returned entry will correspond
> >> + *                    to the timestamp which is <= the requested one, if backward
> >> + *                    is 0, then it will be >=
> >> + *                    if AVSEEK_FLAG_ANY seek to any frame, only keyframes otherwise.
> >> + * @return A pointer to the requested AVIndexEntry if it exists, NULL otherwise.
> >> + *
> >> + * @note The pointer returned by this function is only guaranteed to be valid
> >> + *       until any function that could alter the stream or the AVFormatContext
> >> + *       that cointains it is called.
> > 
> > How can the user know which functions can "alter the stream or the
> > AVFormatContext"?
> 
> Any function that takes a non const AVStream or AVFormatContext should 
> be considered one that can potentially alter the stream.
> 
> > 
> > I would prefer invalidating the pointer on ANY lavf call on that
> > AVFormatContext or its children, including calls to
> > avformat_index_get_entry*. That would allow us more freedom to change
> > the implementation later.
> 
> avformat_index_get_entry() takes a const AVStream after i included 
> Andreas suggestion when i pushed this patch the other day, so in theory 
> it should not change the index array stored within the AVStream. I'd 
> have to remove the const qualifier.
> If that's preferred, I can send a patch to make this change to the doxy 
> and signature.

It seems preferable to me, but YMMV.

-- 
Anton Khirnov