[FFmpeg-devel] [PATCH] lavfi/atempo: raise max tempo limit (v2)

[Pavel Koshevoy]

On Thu, Jun 7, 2018 at 8:16 PM Pavel Koshevoy <pkoshevoy at gmail.com> wrote:
>
> ---
>  doc/filters.texi        | 17 ++++++++++++++---
>  libavfilter/af_atempo.c |  6 +++---
>  2 files changed, 17 insertions(+), 6 deletions(-)
>
> diff --git a/doc/filters.texi b/doc/filters.texi
> index 256ab42b00..6b98b04774 100644
> --- a/doc/filters.texi
> +++ b/doc/filters.texi
> @@ -1986,7 +1986,12 @@ Adjust audio tempo.
>
>  The filter accepts exactly one parameter, the audio tempo. If not
>  specified then the filter will assume nominal 1.0 tempo. Tempo must
> -be in the [0.5, 2.0] range.
> +be in the [0.5, 100.0] range.
> +
> +Note that tempo greater than 2 will skip some samples rather than
> +blend them in.  If for any reason this is a concern it is always
> +possible to daisy-chain several instances of atempo to achieve the
> +desired product tempo.
>
>  @subsection Examples
>
> @@ -1998,9 +2003,15 @@ atempo=0.8
>  @end example
>
>  @item
> -To speed up audio to 125% tempo:
> +To speed up audio to 300% tempo:
> + at example
> +atempo=3
> + at end example
> +
> + at item
> +To speed up audio to 300% tempo by daisy-chaining two atempo instances:
>  @example
> -atempo=1.25
> +atempo=sqrt(3),atempo=sqrt(3)
>  @end example
>  @end itemize
>
> diff --git a/libavfilter/af_atempo.c b/libavfilter/af_atempo.c
> index 8b214bccd7..52f15f2769 100644
> --- a/libavfilter/af_atempo.c
> +++ b/libavfilter/af_atempo.c
> @@ -153,7 +153,7 @@ typedef struct ATempoContext {
>
>  static const AVOption atempo_options[] = {
>      { "tempo", "set tempo scale factor",
> -      OFFSET(tempo), AV_OPT_TYPE_DOUBLE, { .dbl = 1.0 }, 0.5, 2.0,
> +      OFFSET(tempo), AV_OPT_TYPE_DOUBLE, { .dbl = 1.0 }, 0.5, 100.0,
>        AV_OPT_FLAG_AUDIO_PARAM | AV_OPT_FLAG_FILTERING_PARAM },
>      { NULL }
>  };
> @@ -439,8 +439,8 @@ static int yae_load_data(ATempoContext *atempo,
>          return 0;
>      }
>
> -    // samples are not expected to be skipped:
> -    av_assert0(read_size <= atempo->ring);
> +    // samples are not expected to be skipped, unless tempo is greater than 2:
> +    av_assert0(read_size <= atempo->ring || atempo->tempo > 2.0);
>
>      while (atempo->position[0] < stop_here && src < src_end) {
>          int src_samples = (src_end - src) / atempo->stride;
> --
> 2.16.4
>


Any objections if I apply this?

    Pavel.