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ffmpeg: implement -force_key_frames expression evalution

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1 parent 2b14344 commit 43af18ef8bd97123b85c02877aa22a0f4ea56ab5 @saste saste committed Dec 9, 2012
Showing with 112 additions and 5 deletions.
  1. +38 −0 doc/ffmpeg.texi
  2. +60 −5 ffmpeg.c
  3. +14 −0 ffmpeg.h
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38 doc/ffmpeg.texi
@@ -552,9 +552,16 @@ Force video tag/fourcc. This is an alias for @code{-tag:v}.
Show QP histogram
@item -vbsf @var{bitstream_filter}
Deprecated see -bsf
+
@item -force_key_frames[:@var{stream_specifier}] @var{time}[,@var{time}...] (@emph{output,per-stream})
+@item -force_key_frames[:@var{stream_specifier}] expr:@var{expr} (@emph{output,per-stream})
Force key frames at the specified timestamps, more precisely at the first
frames after each specified time.
+
+If the argument is prefixed with @code{expr:}, the string @var{expr}
+is interpreted like an expression and is evaluated for each frame. A
+key frame is forced in case the evaluation is non-zero.
+
If one of the times is "@code{chapters}[@var{delta}]", it is expanded into
the time of the beginning of all chapters in the file, shifted by
@var{delta}, expressed as a time in seconds.
@@ -567,6 +574,37 @@ before the beginning of every chapter:
-force_key_frames 0:05:00,chapters-0.1
@end example
+The expression in @var{expr} can contain the following constants:
+@table @option
+@item n
+the number of current processed frame, starting from 0
+@item n_forced
+the number of forced frames
+@item prev_forced_n
+the number of the previous forced frame, it is @code{NAN} when no
+keyframe was forced yet
+@item prev_forced_t
+the time of the previous forced frame, it is @code{NAN} when no
+keyframe was forced yet
+@item t
+the time of the current processed frame
+@end table
+
+For example to force a key frame every 5 seconds, you can specify:
+@example
+-force_key_frames expr:gte(t,n_forced*5)
+@end example
+
+To force a key frame 5 seconds after the time of the last forced one,
+starting from second 13:
+@example
+-force_key_frames expr:if(isnan(prev_forced_t),gte(t,13),gte(t,prev_forced_t+5))
+@end example
+
+Note that forcing too many keyframes is very harmful for the lookahead
+algorithms of certain encoders: using fixed-GOP options or similar
+would be more efficient.
+
@item -copyinkf[:@var{stream_specifier}] (@emph{output,per-stream})
When doing stream copy, copy also non-key frames found at the
beginning.
View
65 ffmpeg.c
@@ -109,6 +109,15 @@ const int program_birth_year = 2000;
static FILE *vstats_file;
+const char *const forced_keyframes_const_names[] = {
+ "n",
+ "n_forced",
+ "prev_forced_n",
+ "prev_forced_t",
+ "t",
+ NULL
+};
+
static void do_video_stats(OutputStream *ost, int frame_size);
static int64_t getutime(void);
@@ -437,6 +446,7 @@ static void exit_program(void)
avcodec_free_frame(&output_streams[i]->filtered_frame);
av_freep(&output_streams[i]->forced_keyframes);
+ av_expr_free(output_streams[i]->forced_keyframes_pexpr);
av_freep(&output_streams[i]->avfilter);
av_freep(&output_streams[i]->logfile_prefix);
av_freep(&output_streams[i]);
@@ -873,8 +883,9 @@ static void do_video_out(AVFormatContext *s,
video_size += pkt.size;
write_frame(s, &pkt, ost);
} else {
- int got_packet;
+ int got_packet, forced_keyframe = 0;
AVFrame big_picture;
+ double pts_time;
big_picture = *in_picture;
/* better than nothing: use input picture interlaced
@@ -898,11 +909,41 @@ static void do_video_out(AVFormatContext *s,
big_picture.quality = ost->st->codec->global_quality;
if (!enc->me_threshold)
big_picture.pict_type = 0;
+
+ pts_time = big_picture.pts != AV_NOPTS_VALUE ?
+ big_picture.pts * av_q2d(enc->time_base) : NAN;
if (ost->forced_kf_index < ost->forced_kf_count &&
big_picture.pts >= ost->forced_kf_pts[ost->forced_kf_index]) {
- big_picture.pict_type = AV_PICTURE_TYPE_I;
ost->forced_kf_index++;
+ forced_keyframe = 1;
+ } else if (ost->forced_keyframes_pexpr) {
+ double res;
+ ost->forced_keyframes_expr_const_values[FKF_T] = pts_time;
+ res = av_expr_eval(ost->forced_keyframes_pexpr,
+ ost->forced_keyframes_expr_const_values, NULL);
+ av_dlog(NULL, "force_key_frame: n:%f n_forced:%f prev_forced_n:%f t:%f prev_forced_t:%f -> res:%f\n",
+ ost->forced_keyframes_expr_const_values[FKF_N],
+ ost->forced_keyframes_expr_const_values[FKF_N_FORCED],
+ ost->forced_keyframes_expr_const_values[FKF_PREV_FORCED_N],
+ ost->forced_keyframes_expr_const_values[FKF_T],
+ ost->forced_keyframes_expr_const_values[FKF_PREV_FORCED_T],
+ res);
+ if (res) {
+ forced_keyframe = 1;
+ ost->forced_keyframes_expr_const_values[FKF_PREV_FORCED_N] =
+ ost->forced_keyframes_expr_const_values[FKF_N];
+ ost->forced_keyframes_expr_const_values[FKF_PREV_FORCED_T] =
+ ost->forced_keyframes_expr_const_values[FKF_T];
+ ost->forced_keyframes_expr_const_values[FKF_N_FORCED] += 1;
+ }
+
+ ost->forced_keyframes_expr_const_values[FKF_N] += 1;
+ }
+ if (forced_keyframe) {
+ big_picture.pict_type = AV_PICTURE_TYPE_I;
+ av_log(NULL, AV_LOG_DEBUG, "Forced keyframe at time %f\n", pts_time);
}
+
update_benchmark(NULL);
ret = avcodec_encode_video2(enc, &pkt, &big_picture, &got_packet);
update_benchmark("encode_video %d.%d", ost->file_index, ost->index);
@@ -2272,9 +2313,23 @@ static int transcode_init(void)
codec->bits_per_raw_sample = frame_bits_per_raw_sample;
}
- if (ost->forced_keyframes)
- parse_forced_key_frames(ost->forced_keyframes, ost,
- ost->st->codec);
+ if (ost->forced_keyframes) {
+ if (!strncmp(ost->forced_keyframes, "expr:", 5)) {
+ ret = av_expr_parse(&ost->forced_keyframes_pexpr, ost->forced_keyframes+5,
+ forced_keyframes_const_names, NULL, NULL, NULL, NULL, 0, NULL);
+ if (ret < 0) {
+ av_log(NULL, AV_LOG_ERROR,
+ "Invalid force_key_frames expression '%s'\n", ost->forced_keyframes+5);
+ return ret;
+ }
+ ost->forced_keyframes_expr_const_values[FKF_N] = 0;
+ ost->forced_keyframes_expr_const_values[FKF_N_FORCED] = 0;
+ ost->forced_keyframes_expr_const_values[FKF_PREV_FORCED_N] = NAN;
+ ost->forced_keyframes_expr_const_values[FKF_PREV_FORCED_T] = NAN;
+ } else {
+ parse_forced_key_frames(ost->forced_keyframes, ost, ost->st->codec);
+ }
+ }
break;
case AVMEDIA_TYPE_SUBTITLE:
codec->time_base = (AVRational){1, 1000};
View
14 ffmpeg.h
@@ -41,6 +41,7 @@
#include "libavutil/avutil.h"
#include "libavutil/dict.h"
+#include "libavutil/eval.h"
#include "libavutil/fifo.h"
#include "libavutil/pixfmt.h"
#include "libavutil/rational.h"
@@ -289,6 +290,17 @@ typedef struct InputFile {
#endif
} InputFile;
+enum forced_keyframes_const {
+ FKF_N,
+ FKF_N_FORCED,
+ FKF_PREV_FORCED_N,
+ FKF_PREV_FORCED_T,
+ FKF_T,
+ FKF_NB
+};
+
+extern const char *const forced_keyframes_const_names[];
+
typedef struct OutputStream {
int file_index; /* file index */
int index; /* stream index in the output file */
@@ -320,6 +332,8 @@ typedef struct OutputStream {
int forced_kf_count;
int forced_kf_index;
char *forced_keyframes;
+ AVExpr *forced_keyframes_pexpr;
+ double forced_keyframes_expr_const_values[FKF_NB];
/* audio only */
int audio_channels_map[SWR_CH_MAX]; /* list of the channels id to pick from the source stream */

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