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avcodec/aacenc: add strict bit rate control option 

In certain use cases, controlling the maximum frame size is critical. An
example is when transmitting AAC packets over Bluetooth A2DP.

While the spec allows the packets to be fragmented (but UNRECOMMENDED),
in practice most headsets do not recognize nor reassemble such packets.

In this patch, we allow setting `bit_rate_tolerance` to 0 to indicate
that the specified bit rate should be treated as an upper bound up to
frame level.

Signed-off-by: Jeremy Wu <jrwu@chromium.org>
This commit is contained in:
Jeremy Wu 2023-04-25 06:09:52 +00:00 committed by Lynne
parent 378fb40282
commit b92af7b64e
2 changed files with 13 additions and 1 deletions
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12
libavcodec/aacenc.c
View File

@ -1106,6 +1106,18 @@ static int aac_encode_frame(AVCodecContext *avctx, AVPacket *avpkt,
too_many_bits = FFMIN(too_many_bits, 6144 * s->channels - 3);
too_few_bits = FFMIN(FFMAX(rate_bits - rate_bits/4, target_bits), too_many_bits);
/* When strict bit-rate control is demanded */
if (avctx->bit_rate_tolerance == 0) {
if (rate_bits < frame_bits) {
float ratio = ((float)rate_bits) / frame_bits;
s->lambda *= FFMIN(0.9f, ratio);
continue;
}
/* reset lambda when solution is found */
s->lambda = avctx->global_quality > 0 ? avctx->global_quality : 120;
break;
}
/* When using ABR, be strict (but only for increasing) */
too_few_bits = too_few_bits - too_few_bits/8;
too_many_bits = too_many_bits + too_many_bits/2;

2
libavcodec/options_table.h
View File

@ -50,7 +50,7 @@ static const AVOption avcodec_options[] = {
{"bt", "Set video bitrate tolerance (in bits/s). In 1-pass mode, bitrate tolerance specifies how far "
"ratecontrol is willing to deviate from the target average bitrate value. This is not related "
"to minimum/maximum bitrate. Lowering tolerance too much has an adverse effect on quality.",
OFFSET(bit_rate_tolerance), AV_OPT_TYPE_INT, {.i64 = AV_CODEC_DEFAULT_BITRATE*20 }, 1, INT_MAX, V|E},
OFFSET(bit_rate_tolerance), AV_OPT_TYPE_INT, {.i64 = AV_CODEC_DEFAULT_BITRATE*20 }, 0, INT_MAX, A|V|E},
{"flags", NULL, OFFSET(flags), AV_OPT_TYPE_FLAGS, {.i64 = DEFAULT }, 0, UINT_MAX, V|A|S|E|D, "flags"},
{"unaligned", "allow decoders to produce unaligned output", 0, AV_OPT_TYPE_CONST, { .i64 = AV_CODEC_FLAG_UNALIGNED }, INT_MIN, INT_MAX, V | D, "flags" },
{"mv4", "use four motion vectors per macroblock (MPEG-4)", 0, AV_OPT_TYPE_CONST, {.i64 = AV_CODEC_FLAG_4MV }, INT_MIN, INT_MAX, V|E, "flags"},