[FFmpeg-devel] [PATCH] avformat/file: add seekable option to disallow seeking

[Hendrik Leppkes]

On Wed, Apr 3, 2019 at 10:42 PM Marton Balint <cus at passwd.hu> wrote:
>
> Signed-off-by: Marton Balint <cus at passwd.hu>
> ---
>  doc/protocols.texi | 9 +++++++++
>  libavformat/file.c | 5 +++++
>  2 files changed, 14 insertions(+)
>
> diff --git a/doc/protocols.texi b/doc/protocols.texi
> index e1caa049a5..34967ff5e2 100644
> --- a/doc/protocols.texi
> +++ b/doc/protocols.texi
> @@ -199,6 +199,15 @@ If set to 1, the protocol will retry reading at the end of the file, allowing
>  reading files that still are being written. In order for this to terminate,
>  you either need to use the rw_timeout option, or use the interrupt callback
>  (for API users).
> +
> + at item seekable
> +Controls if seekability is advertised on the file. 1 means seekable, 0 means
> +non-seekable, -1 means auto (seekable for normal files, non-seekable for named
> +pipes).
> +
> +Many demuxers handle seekable and non-seekable resources differently,
> +overriding this might speed up opening certain files at the cost of losing some
> +features (e.g. accurate seeking).
>  @end table
>
>  @section ftp
> diff --git a/libavformat/file.c b/libavformat/file.c
> index e613b91010..e46596fed1 100644
> --- a/libavformat/file.c
> +++ b/libavformat/file.c
> @@ -73,6 +73,7 @@ typedef struct FileContext {
>      int trunc;
>      int blocksize;
>      int follow;
> +    int seekable;
>  #if HAVE_DIRENT_H
>      DIR *dir;
>  #endif
> @@ -82,6 +83,7 @@ static const AVOption file_options[] = {
>      { "truncate", "truncate existing files on write", offsetof(FileContext, trunc), AV_OPT_TYPE_BOOL, { .i64 = 1 }, 0, 1, AV_OPT_FLAG_ENCODING_PARAM },
>      { "blocksize", "set I/O operation maximum block size", offsetof(FileContext, blocksize), AV_OPT_TYPE_INT, { .i64 = INT_MAX }, 1, INT_MAX, AV_OPT_FLAG_ENCODING_PARAM },
>      { "follow", "Follow a file as it is being written", offsetof(FileContext, follow), AV_OPT_TYPE_INT, { .i64 = 0 }, 0, 1, AV_OPT_FLAG_DECODING_PARAM },
> +    { "seekable", "Sets if the file is seekable", offsetof(FileContext, seekable), AV_OPT_TYPE_INT, { .i64 = -1 }, -1, 1, AV_OPT_FLAG_DECODING_PARAM | AV_OPT_FLAG_ENCODING_PARAM },
>      { NULL }
>  };
>
> @@ -238,6 +240,9 @@ static int file_open(URLContext *h, const char *filename, int flags)
>      if (!h->is_streamed && flags & AVIO_FLAG_WRITE)
>          h->min_packet_size = h->max_packet_size = 262144;
>
> +    if (c->seekable >= 0)
> +        h->is_streamed = !c->seekable;
> +

You should probably not let a user enable seeking if the resource
doesn't allow it.

- Hendrik