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

[Pavel Koshevoy]

---
 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