[FFmpeg-devel] [PATCH 2/2] avcodec/libmp3lame: add ABR support

[Timothy Gu]

Signed-off-by: Timothy Gu <timothygu99 at gmail.com>
---
 doc/encoders.texi       | 7 ++++++-
 libavcodec/libmp3lame.c | 6 ++++++
 2 files changed, 12 insertions(+), 1 deletion(-)

diff --git a/doc/encoders.texi b/doc/encoders.texi
index a96c1fc..fc44f3a 100644
--- a/doc/encoders.texi
+++ b/doc/encoders.texi
@@ -509,7 +509,7 @@ The following options are supported by the libmp3lame wrapper. The
 
 @table @option
 @item b (@emph{-b})
-Set bitrate expressed in bits/s for CBR. LAME @code{bitrate} is
+Set bitrate expressed in bits/s for CBR or ABR. LAME @code{bitrate} is
 expressed in kilobits/s.
 
 @item q (@emph{-V})
@@ -531,6 +531,11 @@ has this enabled by default, but can be overriden by use
 Enable the encoder to use (on a frame by frame basis) either L/R
 stereo or mid/side stereo. Default value is 1.
 
+ at item abr (@emph{--abr})
+Enable the encoder to use ABR when set to 1. The @command{lame}
+ at option{--abr} sets the target bitrate, while this options only
+tells FFmpeg to use ABR still relies on @option{b} to set bitrate.
+
 @end table
 
 @section libopencore-amrnb
diff --git a/libavcodec/libmp3lame.c b/libavcodec/libmp3lame.c
index 9cd2f46..00d3023 100644
--- a/libavcodec/libmp3lame.c
+++ b/libavcodec/libmp3lame.c
@@ -49,6 +49,7 @@ typedef struct LAMEContext {
     int buffer_size;
     int reservoir;
     int joint_stereo;
+    int abr;
     float *samples_flt[2];
     AudioFrameQueue afq;
     AVFloatDSPContext fdsp;
@@ -121,6 +122,10 @@ static av_cold int mp3lame_encode_init(AVCodecContext *avctx)
     } else {
         if (avctx->bit_rate)                // CBR
             lame_set_brate(s->gfp, avctx->bit_rate / 1000);
+        else if (s->abr) {                  // ABR
+            lame_set_VBR(gfp, vbr_abr);
+            lame_set_VBR_mean_bitrate_kbps(gfp, avctx->bit_rate / 1000);
+        }
     }
 
     /* do not get a Xing VBR header frame from LAME */
@@ -265,6 +270,7 @@ static int mp3lame_encode_frame(AVCodecContext *avctx, AVPacket *avpkt,
 static const AVOption options[] = {
     { "reservoir",    "Use bit reservoir.", OFFSET(reservoir),    AV_OPT_TYPE_INT, { .i64 = 1 }, 0, 1, AE },
     { "joint_stereo", "Use joint stereo.",  OFFSET(joint_stereo), AV_OPT_TYPE_INT, { .i64 = 1 }, 0, 1, AE },
+    { "abr",          "Use ABR.",           OFFSET(abr),          AV_OPT_TYPE_INT, { .i64 = 0 }, 0, 1, AE },
     { NULL },
 };
 
-- 
1.8.1.2