[FFmpeg-cvslog] doc/encoders/libopus: clarify lowdelay and cutoff options
Stefano Sabatini
git at videolan.org
Fri Oct 6 10:53:35 EEST 2023
ffmpeg | branch: master | Stefano Sabatini <stefasab at gmail.com> | Sat Aug 26 15:45:33 2023 +0200| [00eb4966aa8a71a70c4758254027fdc6925f8f86] | committer: Stefano Sabatini
doc/encoders/libopus: clarify lowdelay and cutoff options
Extend descriptions for the application=lowdelay and cutoff options.
Based on notes by Mingye Wang.
Address issues:
http://trac.ffmpeg.org/ticket/10330
http://trac.ffmpeg.org/ticket/10343
> http://git.videolan.org/gitweb.cgi/ffmpeg.git/?a=commit;h=00eb4966aa8a71a70c4758254027fdc6925f8f86
---
doc/encoders.texi | 7 +++++--
libavcodec/libopusenc.c | 2 +-
2 files changed, 6 insertions(+), 3 deletions(-)
diff --git a/doc/encoders.texi b/doc/encoders.texi
index a6fef8a8f4..8b2ab937d1 100644
--- a/doc/encoders.texi
+++ b/doc/encoders.texi
@@ -977,14 +977,17 @@ Favor improved speech intelligibility.
@item audio
Favor faithfulness to the input (the default).
@item lowdelay
-Restrict to only the lowest delay modes.
+Restrict to only the lowest delay modes by disabling voice-optimized
+modes.
@end table
@item cutoff (N.A.)
Set cutoff bandwidth in Hz. The argument must be exactly one of the
following: 4000, 6000, 8000, 12000, or 20000, corresponding to
narrowband, mediumband, wideband, super wideband, and fullband
-respectively. The default is 0 (cutoff disabled).
+respectively. The default is 0 (cutoff disabled). Note that libopus
+forces a wideband cutoff for bitrates < 15 kbps, unless CELT-only
+(@option{application} set to @samp{lowdelay}) mode is used.
@item mapping_family (@emph{mapping_family})
Set channel mapping family to be used by the encoder. The default value of -1
diff --git a/libavcodec/libopusenc.c b/libavcodec/libopusenc.c
index 5a0786f32f..f395d84af5 100644
--- a/libavcodec/libopusenc.c
+++ b/libavcodec/libopusenc.c
@@ -547,7 +547,7 @@ static const AVOption libopus_options[] = {
{ "application", "Intended application type", OFFSET(application), AV_OPT_TYPE_INT, { .i64 = OPUS_APPLICATION_AUDIO }, OPUS_APPLICATION_VOIP, OPUS_APPLICATION_RESTRICTED_LOWDELAY, FLAGS, "application" },
{ "voip", "Favor improved speech intelligibility", 0, AV_OPT_TYPE_CONST, { .i64 = OPUS_APPLICATION_VOIP }, 0, 0, FLAGS, "application" },
{ "audio", "Favor faithfulness to the input", 0, AV_OPT_TYPE_CONST, { .i64 = OPUS_APPLICATION_AUDIO }, 0, 0, FLAGS, "application" },
- { "lowdelay", "Restrict to only the lowest delay modes", 0, AV_OPT_TYPE_CONST, { .i64 = OPUS_APPLICATION_RESTRICTED_LOWDELAY }, 0, 0, FLAGS, "application" },
+ { "lowdelay", "Restrict to only the lowest delay modes, disable voice-optimized modes", 0, AV_OPT_TYPE_CONST, { .i64 = OPUS_APPLICATION_RESTRICTED_LOWDELAY }, 0, 0, FLAGS, "application" },
{ "frame_duration", "Duration of a frame in milliseconds", OFFSET(frame_duration), AV_OPT_TYPE_FLOAT, { .dbl = 20.0 }, 2.5, 120.0, FLAGS },
{ "packet_loss", "Expected packet loss percentage", OFFSET(packet_loss), AV_OPT_TYPE_INT, { .i64 = 0 }, 0, 100, FLAGS },
{ "fec", "Enable inband FEC. Expected packet loss must be non-zero", OFFSET(fec), AV_OPT_TYPE_BOOL, { .i64 = 0 }, 0, 1, FLAGS },
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