[FFmpeg-devel] Modified force_key_frames option to accept frame numbers
Sylvester Zaluga
sylvester.zaluga at gmail.com
Mon Nov 10 00:42:32 CET 2014
***Sending again, this time with diff***
Attached a patch which allows for passing in frame numbers
at which key frames should be forced.
The current modes in which force_key_frames operate are:
* force_key_frames 1,2,3,4,5 - parameter is interpreted as timestamps
* force_key_frames expr:gte(t,n_forced) - parameter is an expression
The patch adds support for third mode:
* force_key_frames n:0,25,50,75,100 - interpret parameter as frame numbers
I find this useful for avoiding float precision-related
issues that surface when key frames are forced at specified timestamps.
My use case is as follows:
* generate output video with settings for HD video
* extract key frame numbers from HD video
* generate SD video with key frames at identical positions
* In my application, do video LODing by switching HD/SD video
depending on bandwith
For generating the SD video I was using force_key_frames with timestamps,
but every-so-often a key frame would be forced too early.
The same behaviour could be achieved with an expression, for example:
expr:bitor(eq(n,0),bitor(eq(n,25),bitor(eq(n,50),bitor(eq(n,75),bitor(eq(n,100),0)))))
This, however, is suboptimal, and not very clean. Additionally, there is
a size limit for expressions, so it can not be used for longer videos.
Please let me know any feedback you have on this patch or the approach used.
Thanks,
Sylwester Zaluga
Signed-off-by: Sylwester Zaluga <sylwekzff at outlook.com>
----
diff --git a/doc/ffmpeg.texi b/doc/ffmpeg.texi
index d774aba..5d15f6f 100644
--- a/doc/ffmpeg.texi
+++ b/doc/ffmpeg.texi
@@ -586,9 +586,14 @@ Show QP histogram
Deprecated see -bsf
@item -force_key_frames[:@var{stream_specifier}] @var{time}[, at var{time}...] (@emph{output,per-stream})
+ at item -force_key_frames[:@var{stream_specifier}] n:@var{number}[, at var{number}...] (@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.
+Force key frames at the specified timestamps (more precisely at the first
+frames after each specified time) or at the specified frame numbers.
+
+If the argument is prefixed with @code{n:}, the comma-separated @var{number}
+strings will be interpreted as numbers / indices of frames that should
+be forced to be key frames.
If the argument is prefixed with @code{expr:}, the string @var{expr}
is interpreted like an expression and is evaluated for each frame. A
@@ -606,6 +611,11 @@ before the beginning of every chapter:
-force_key_frames 0:05:00,chapters-0.1
@end example
+For example, to insert at predefined frame numbers:
+ at example
+-force_key_frames n:0,25,50,75,100,125,150,175,200,225,250
+ at end example
+
The expression in @var{expr} can contain the following constants:
@table @option
@item n
diff --git a/ffmpeg.c b/ffmpeg.c
index 1fd0ece..969222d 100644
--- a/ffmpeg.c
+++ b/ffmpeg.c
@@ -1039,6 +1039,11 @@ static void do_video_out(AVFormatContext *s,
}
ost->forced_keyframes_expr_const_values[FKF_N] += 1;
+ } else if (ost->forced_kf_n_index < ost->forced_kf_n_count &&
+ ost->frame_number == ost->forced_kf_n_pts[ost->forced_kf_n_index]) {
+ av_dlog(NULL, "force_key_frame (number mode): n:%d\n", ost->frame_number);
+ ost->forced_kf_n_index++;
+ forced_keyframe = 1;
}
if (forced_keyframe) {
@@ -2333,6 +2338,12 @@ static InputStream *get_input_stream(OutputStream *ost)
return NULL;
}
+static int compare_int(const void *a, const void *b)
+{
+ int va = *(int *)a, vb = *(int *)b;
+ return va < vb ? -1 : va > vb ? +1 : 0;
+}
+
static int compare_int64(const void *a, const void *b)
{
int64_t va = *(int64_t *)a, vb = *(int64_t *)b;
@@ -2402,6 +2413,53 @@ static void parse_forced_key_frames(char *kf, OutputStream *ost,
ost->forced_kf_pts = pts;
}
+static void parse_forced_key_frames_n(char *kf, OutputStream *ost,
+ AVCodecContext *avctx)
+{
+ char *p;
+ int n = 1, i, size, index = 0;
+ int kf_n, kf_n_prev, *pts;
+
+ for (p = kf; *p; p++)
+ if (*p == ',')
+ n++;
+ size = n;
+ pts = av_malloc_array(size, sizeof(*pts));
+ if (!pts) {
+ av_log(NULL, AV_LOG_FATAL, "Could not allocate forced key frames array.\n");
+ exit_program(1);
+ }
+
+ p = kf;
+ for (i = 0; i < n; i++) {
+ char *next = strchr(p, ',');
+
+ if (next)
+ *next++ = 0;
+
+ kf_n = parse_number_or_die("force_key_frames (numbers)", p, OPT_INT, 0, INT_MAX);
+ av_assert1(index < size);
+ pts[index++] = kf_n;
+
+ p = next;
+ }
+
+ av_assert0(index == size);
+ qsort(pts, size, sizeof(*pts), compare_int);
+
+ kf_n_prev = -1;
+ for (i = 0; i < n; i++) {
+ if (pts[i] == kf_n_prev) {
+ av_log(NULL, AV_LOG_FATAL, "Duplicated forced key frame number.\n");
+ exit_program(1);
+ }
+ kf_n_prev = pts[i];
+ }
+
+ ost->forced_kf_n_count = size;
+ ost->forced_kf_n_pts = pts;
+}
+
static void report_new_stream(int input_index, AVPacket *pkt)
{
InputFile *file = input_files[input_index];
@@ -2815,6 +2873,8 @@ static int transcode_init(void)
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 if (!strncmp(ost->forced_keyframes, "n:", 2)) {
+ parse_forced_key_frames_n(ost->forced_keyframes+2, ost, ost->enc_ctx);
} else {
parse_forced_key_frames(ost->forced_keyframes, ost, ost->enc_ctx);
}
@@ -3775,6 +3835,7 @@ static int transcode(void)
ost->logfile = NULL;
}
av_freep(&ost->forced_kf_pts);
+ av_freep(&ost->forced_kf_n_pts);
av_freep(&ost->apad);
av_dict_free(&ost->encoder_opts);
av_dict_free(&ost->swr_opts);
diff --git a/ffmpeg.h b/ffmpeg.h
index c456603..539b8bd 100644
--- a/ffmpeg.h
+++ b/ffmpeg.h
@@ -400,6 +400,9 @@ typedef struct OutputStream {
int64_t *forced_kf_pts;
int forced_kf_count;
int forced_kf_index;
+ int *forced_kf_n_pts; /* list of forced key frame numbers / indices */
+ int forced_kf_n_count; /* count of forced key frame numbers / indices */
+ int forced_kf_n_index; /* current numbered forced key frame */
char *forced_keyframes;
AVExpr *forced_keyframes_pexpr;
double forced_keyframes_expr_const_values[FKF_NB];
diff --git a/ffmpeg_opt.c b/ffmpeg_opt.c
index 77ef0c4..15c4813 100644
--- a/ffmpeg_opt.c
+++ b/ffmpeg_opt.c
@@ -2990,7 +2990,7 @@ const OptionDef options[] = {
"set the value of an outfile streamid", "streamIndex:value" },
{ "force_key_frames", OPT_VIDEO | OPT_STRING | HAS_ARG | OPT_EXPERT |
OPT_SPEC | OPT_OUTPUT, { .off = OFFSET(forced_key_frames) },
- "force key frames at specified timestamps", "timestamps" },
+ "force key frames at specified timestamps or frame numbers", "timestamps/frame numbers" },
{ "ab", OPT_VIDEO | HAS_ARG | OPT_PERFILE | OPT_OUTPUT, { .func_arg = opt_bitrate },
"audio bitrate (please use -b:a)", "bitrate" },
{ "b", OPT_VIDEO | HAS_ARG | OPT_PERFILE | OPT_OUTPUT, { .func_arg = opt_bitrate },
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