[FFmpeg-devel] [RFC] possible API for opening external demuxer references

[Baptiste Coudurier]

Reimar D?ffinger wrote:
> Hello,
> currently just a flag probably is good enough, but in case someone is
> interested in taking things further (maybe even as a way to implement
> general playlist support in lavf, including rules like "internet
> playlists can only reference internet files and vice versa"?) here is
> a first idea of a possible API.
> Probably it makes little sense without actually implementing things to
> actually see how suitable it is, but since I already got that far...
> 
> Greetings,
> Reimar D?ffinger
> 
> 
> ------------------------------------------------------------------------
> 
> diff --git a/libavformat/avformat.h b/libavformat/avformat.h
> index ad186e4..8f0cfa8 100644
> --- a/libavformat/avformat.h
> +++ b/libavformat/avformat.h
> @@ -499,6 +499,12 @@ typedef struct AVFormatContext {
>       * demuxing: set by user
>       */
>      unsigned int max_index_size;
> +
> +    //! Callback used to open a substream referenced by a container
> +    int (*open_stream)(struct AVFormatContext *, ByteIOContext **s,
> +                       const uint8_t *resource, int resource_length, int flags);
> +    //! Custom user data for use by e.g. open_stream callback
> +    void *user_data;
>  } AVFormatContext;

Humm not sure, but is AVFormatContext arg needed here ?

Problem is open_stream prototype is incompatible with url_fopen.

>  typedef struct AVPacketList {
> diff --git a/libavformat/mov.c b/libavformat/mov.c
> index 0b3c0a4..ba28f39 100644
> --- a/libavformat/mov.c
> +++ b/libavformat/mov.c
> @@ -1534,11 +1534,15 @@ static int mov_read_header(AVFormatContext *s, AVFormatParameters *ap)
>          sc->ffindex = i;
>          mov_build_index(mov, st);
>  
> +        sc->pb = NULL;
>          if (sc->dref_id-1 < sc->drefs_count && sc->drefs[sc->dref_id-1].path) {
> -            if (url_fopen(&sc->pb, sc->drefs[sc->dref_id-1].path, URL_RDONLY) < 0)
> +            if (s->open_stream &&
> +                s->open_stream(s, &sc->pb, sc->drefs[sc->dref_id-1].path,
> +                            strlen(sc->drefs[sc->dref_id-1].path), URL_RDONLY) < 0)
>                  av_log(s, AV_LOG_ERROR, "stream %d, error opening external essence: %s\n",
>                         st->index, strerror(errno));
> -        } else
> +        }
> +        if (!sc->pb)
>              sc->pb = s->pb;

If stream is detected as external, sc->pb must not be set, else it will
demux garbage data.
Also I'd like url_fopen to be used as a fallback, if the
AVFMT_FLAG_EXTREF flag is set, or another mechanism.

-- 
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