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avformat/lrcenc: add precision option

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Allows to output LRC with more precision than standard centiseconds.
Time base is determined by number of requested digits.

Signed-off-by: Kacper Michajłow <kasper93@gmail.com>
This commit is contained in:
Kacper Michajłow
2025-07-23 23:55:16 +02:00
parent a29aeee37e
commit 670c1b9266
2 changed files with 50 additions and 6 deletions
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14
doc/encoders.texi
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@ -4629,4 +4629,18 @@ one byte per subtitle on average.
By default, this work-around is disabled.
@end table
@section lrc
This codec encodes the LRC lyrics format.
@subsection Options
@table @option
@item precision
Specify the precision of the fractional part of the timestamp. Time base is
determined based on this value.
Defaults to 2 for centiseconds.
@end table
@c man end SUBTITLES ENCODERS

42
libavformat/lrcenc.c
View File

@ -32,6 +32,12 @@
#include "libavutil/dict.h"
#include "libavutil/log.h"
#include "libavutil/macros.h"
#include "libavutil/opt.h"
typedef struct LRCSubtitleContext {
const AVClass *class;
int precision; ///< precision of the fractional part of the timestamp, 2 for centiseconds
} LRCSubtitleContext;
static int lrc_write_header(AVFormatContext *s)
{
@ -43,7 +49,7 @@ static int lrc_write_header(AVFormatContext *s)
avcodec_get_name(s->streams[0]->codecpar->codec_id));
return AVERROR(EINVAL);
}
avpriv_set_pts_info(s->streams[0], 64, 1, 100);
avpriv_set_pts_info(s->streams[0], 64, 1, AV_TIME_BASE);
ff_standardize_creation_time(s);
ff_metadata_conv_ctx(s, ff_lrc_metadata_conv, NULL);
@ -77,6 +83,8 @@ static int lrc_write_header(AVFormatContext *s)
static int lrc_write_packet(AVFormatContext *s, AVPacket *pkt)
{
const LRCSubtitleContext *p = s->priv_data;
if(pkt->pts != AV_NOPTS_VALUE) {
const uint8_t *line = pkt->data;
const uint8_t *end = pkt->data + pkt->size;
@ -88,6 +96,10 @@ static int lrc_write_packet(AVFormatContext *s, AVPacket *pkt)
line++; // Skip first empty lines
}
int frac_mult = 1;
for (int i = 0; i < p->precision; ++i)
frac_mult *= 10;
while(line) {
const uint8_t *next_line = memchr(line, '\n', end - line);
size_t size = end - line;
@ -105,11 +117,14 @@ static int lrc_write_packet(AVFormatContext *s, AVPacket *pkt)
/* Offset feature of LRC can easily make pts negative,
* we just output it directly and let the player drop it. */
uint64_t abs_pts = FFABS64U(pkt->pts);
uint64_t minutes = abs_pts / (60 * AV_TIME_BASE);
uint64_t seconds = (abs_pts / AV_TIME_BASE) % 60;
uint64_t fraction = abs_pts % AV_TIME_BASE;
uint64_t rescaled = av_rescale_q(fraction, AV_TIME_BASE_Q, (AVRational){1, frac_mult});
avio_write(s->pb, "[-", 1 + (pkt->pts < 0));
avio_printf(s->pb, "%02"PRIu64":%02"PRIu64".%02"PRIu64"]",
(FFABS64U(pkt->pts) / 6000),
((FFABS64U(pkt->pts) / 100) % 60),
(FFABS64U(pkt->pts) % 100));
avio_printf(s->pb, "%02"PRIu64":%02"PRIu64".%0*"PRIu64"]",
minutes, seconds, p->precision, rescaled);
avio_write(s->pb, line, size);
avio_w8(s->pb, '\n');
@ -119,6 +134,20 @@ static int lrc_write_packet(AVFormatContext *s, AVPacket *pkt)
return 0;
}
#define OFFSET(x) offsetof(LRCSubtitleContext, x)
#define SE AV_OPT_FLAG_SUBTITLE_PARAM | AV_OPT_FLAG_ENCODING_PARAM
static const AVOption options[] = {
{"precision", "precision of the fractional part of the timestamp, 2 for centiseconds", OFFSET(precision), AV_OPT_TYPE_INT, {.i64 = 2}, 1, 6, SE},
{ NULL },
};
static const AVClass lrcenc_class = {
.class_name = "lrc",
.item_name = av_default_item_name,
.option = options,
.version = LIBAVUTIL_VERSION_INT,
};
const FFOutputFormat ff_lrc_muxer = {
.p.name = "lrc",
.p.long_name = NULL_IF_CONFIG_SMALL("LRC lyrics"),
@ -129,7 +158,8 @@ const FFOutputFormat ff_lrc_muxer = {
.p.audio_codec = AV_CODEC_ID_NONE,
.p.subtitle_codec = AV_CODEC_ID_SUBRIP,
.flags_internal = FF_OFMT_FLAG_MAX_ONE_OF_EACH,
.priv_data_size = 0,
.priv_data_size = sizeof(LRCSubtitleContext),
.write_header = lrc_write_header,
.write_packet = lrc_write_packet,
.p.priv_class = &lrcenc_class,
};