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From: ihy123 <aladinandreyy@gmail.com>
Date: Sun, 17 Aug 2025 17:27:20 +0300
Subject: ip/ffmpeg: better frame skipping logic
---
ip/ffmpeg.c | 82 ++++++++++++++++++++++++++++++-------------------------------
1 file changed, 41 insertions(+), 41 deletions(-)
diff --git a/ip/ffmpeg.c b/ip/ffmpeg.c
index 71cc511..af6ecfb 100644
--- a/ip/ffmpeg.c
+++ b/ip/ffmpeg.c
@@ -44,8 +44,8 @@ struct ffmpeg_private {
AVPacket *pkt;
AVFrame *frame;
- int64_t seek_ts;
- int64_t prev_frame_end;
+ double seek_ts;
+ int64_t skip_samples;
/* A buffer to hold swr_convert()-ed samples */
AVFrame *swr_frame;
@@ -249,7 +249,6 @@ static int ffmpeg_open(struct input_plugin_data *ip_data)
priv.pkt = av_packet_alloc();
priv.frame = av_frame_alloc();
priv.seek_ts = -1;
- priv.prev_frame_end = -1;
priv.swr = swr_alloc();
ffmpeg_set_sf_and_swr_opts(priv.swr, priv.codec_ctx,
@@ -283,37 +282,37 @@ static int ffmpeg_close(struct input_plugin_data *ip_data)
return 0;
}
-/*
- * return:
- * 0 - retry
- * >0 - ok
- */
-static int ffmpeg_seek_into_frame(struct ffmpeg_private *priv, int64_t frame_ts)
+static int64_t ffmpeg_calc_skip_samples(struct ffmpeg_private *priv)
{
- if (frame_ts >= 0) {
- AVStream *s = priv->format_ctx->streams[priv->stream_index];
- frame_ts = av_rescale_q(frame_ts, s->time_base, AV_TIME_BASE_Q);
+ int64_t ts;
+ if (priv->frame->pts >= 0) {
+ ts = priv->frame->pts;
+ } else if (priv->frame->pkt_dts >= 0) {
+ ts = priv->frame->pkt_dts;
} else {
- frame_ts = priv->prev_frame_end;
+ d_print("AVFrame.pts and AVFrame.pkt_dts are unset\n");
+ return -1;
}
- if (frame_ts >= priv->seek_ts)
- return 1;
-
- int64_t frame_dur = av_rescale(priv->frame->nb_samples,
- AV_TIME_BASE, priv->frame->sample_rate);
- int64_t frame_end = frame_ts + frame_dur;
- priv->prev_frame_end = frame_end;
+ AVStream *s = priv->format_ctx->streams[priv->stream_index];
+ double frame_ts = ts * av_q2d(s->time_base);
- d_print("seek_ts: %ld, frame_ts: %ld, frame_end: %ld\n",
- priv->seek_ts, frame_ts, frame_end);
+ d_print("seek_ts: %.6fs, frame_ts: %.6fs\n", priv->seek_ts, frame_ts);
- if (frame_end <= priv->seek_ts)
+ if (frame_ts >= priv->seek_ts)
return 0;
+ return (priv->seek_ts - frame_ts) * priv->frame->sample_rate;
+}
- int64_t skip_samples = av_rescale(priv->seek_ts - frame_ts,
- priv->frame->sample_rate, AV_TIME_BASE);
- priv->frame->nb_samples -= skip_samples;
+static void ffmpeg_skip_frame_part(struct ffmpeg_private *priv)
+{
+ if (priv->skip_samples >= priv->frame->nb_samples) {
+ d_print("skipping frame: %d samples\n",
+ priv->frame->nb_samples);
+ priv->skip_samples -= priv->frame->nb_samples;
+ priv->frame->nb_samples = 0;
+ return;
+ }
int bps = av_get_bytes_per_sample(priv->frame->format);
#if LIBAVCODEC_VERSION_INT >= AV_VERSION_INT(59, 24, 100)
@@ -322,15 +321,17 @@ static int ffmpeg_seek_into_frame(struct ffmpeg_private *priv, int64_t frame_ts)
int channels = priv->codec_ctx->channels;
#endif
+ priv->frame->nb_samples -= priv->skip_samples;
+
/* Just modify frame's data pointer because it's throw-away */
if (av_sample_fmt_is_planar(priv->frame->format)) {
for (int i = 0; i < channels; i++)
- priv->frame->extended_data[i] += skip_samples * bps;
+ priv->frame->extended_data[i] += priv->skip_samples * bps;
} else {
- priv->frame->extended_data[0] += skip_samples * channels * bps;
+ priv->frame->extended_data[0] += priv->skip_samples * channels * bps;
}
- d_print("skipping %ld samples\n", skip_samples);
- return 1;
+ d_print("skipping %ld samples\n", priv->skip_samples);
+ priv->skip_samples = 0;
}
/*
@@ -361,17 +362,16 @@ static int ffmpeg_get_frame(struct ffmpeg_private *priv)
if (res < 0)
return res;
- int64_t frame_ts = -1;
- if (priv->frame->pts >= 0)
- frame_ts = priv->frame->pts;
- else if (priv->frame->pkt_dts >= 0)
- frame_ts = priv->frame->pkt_dts;
+ if (priv->seek_ts > 0) {
+ priv->skip_samples = ffmpeg_calc_skip_samples(priv);
+ if (priv->skip_samples >= 0)
+ priv->seek_ts = -1;
+ }
- if (priv->seek_ts > 0 && (frame_ts >= 0 || priv->prev_frame_end >= 0)) {
- if (ffmpeg_seek_into_frame(priv, frame_ts) == 0)
+ if (priv->skip_samples > 0) {
+ ffmpeg_skip_frame_part(priv);
+ if (priv->frame->nb_samples == 0)
return 0;
- priv->seek_ts = -1;
- priv->prev_frame_end = -1;
}
return 1;
}
@@ -434,8 +434,8 @@ static int ffmpeg_seek(struct input_plugin_data *ip_data, double offset)
struct ffmpeg_private *priv = ip_data->private;
AVStream *st = priv->format_ctx->streams[priv->stream_index];
- priv->seek_ts = offset * AV_TIME_BASE;
- priv->prev_frame_end = -1;
+ priv->seek_ts = offset;
+ priv->skip_samples = 0;
int64_t ts = av_rescale(offset, st->time_base.den, st->time_base.num);
int ret = avformat_seek_file(priv->format_ctx,
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