[FFmpeg-devel] [PATCH] ffmpeg: implement -force_key_frames_expr option
Nicolas George
nicolas.george at normalesup.org
Thu Dec 13 16:53:57 CET 2012
Le tridi 23 frimaire, an CCXXI, Stefano Sabatini a écrit :
> ---
> doc/ffmpeg.texi | 20 ++++++++++++++++++++
> ffmpeg.c | 44 ++++++++++++++++++++++++++++++++++++++++++--
> ffmpeg.h | 15 +++++++++++++++
> ffmpeg_opt.c | 7 +++++++
> 4 files changed, 84 insertions(+), 2 deletions(-)
>
> diff --git a/doc/ffmpeg.texi b/doc/ffmpeg.texi
> index b8f6930..ff14e04 100644
> --- a/doc/ffmpeg.texi
> +++ b/doc/ffmpeg.texi
> @@ -551,12 +551,32 @@ 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}[, at var{time}...] (@emph{output,per-stream})
> Force key frames at the specified timestamps, more precisely at the first
> frames after each specified time.
> This option can be useful to ensure that a seek point is present at a
> chapter mark or any other designated place in the output file.
> The timestamps must be specified in ascending order.
> +See also the @option{force_key_frames_expr} option.
> +
> + at item -force_key_frames_expr[:@var{stream_specifier}] @var{expr} (@emph{output,per-stream})
> +Force key frames at the time specified by the expression in
... at the times specified by the expression. The expression will be
evaluated repeatedly to get the time for each forced keyframe.
> + at var{expr}, more precisely at the first frames after each specified
> +time. The expression can contain the following constants:
> +
> + at table @option
> + at item n
> +The count of the next match, starting from 0.
Number of already forced keyframes.
> + at item prev_t
> +The time of the last forced key frame, it is @code{NAN} when no
^
(value of the last evaluation of the expression)
> +keyframe was still forced.
... was forced yet.
> + at end table
> +
> +For example you can specify the expression @code{n*5} to force a key
> +frame every 5 seconds, or @code{prev_t+5} to specify a key frame after
> +the last one forced.
> +See also the @option{force_key_frames} option.
Please add a note that forcing too many keyframes is very harmful for the
lookahead algorithms (at least for x264): 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
> diff --git a/ffmpeg.c b/ffmpeg.c
> index 956f5b6..7985051 100644
> --- a/ffmpeg.c
> +++ b/ffmpeg.c
> @@ -109,6 +109,13 @@ const int program_birth_year = 2000;
>
> static FILE *vstats_file;
>
> +const char *const forced_keyframes_const_names[] = {
> + "n",
> + "prev_t",
> + "next_t",
Undocumented?
> + NULL
> +};
> +
> static void do_video_stats(OutputStream *ost, int frame_size);
> static int64_t getutime(void);
>
> @@ -435,6 +442,8 @@ static void exit_program(void)
> avcodec_free_frame(&output_streams[i]->filtered_frame);
>
> av_freep(&output_streams[i]->forced_keyframes);
> + av_freep(&output_streams[i]->forced_keyframes_expr);
> + 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]);
> @@ -872,8 +881,9 @@ 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
> @@ -897,11 +907,26 @@ 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;
Indentation is unusual.
> 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 (pts_time != AV_NOPTS_VALUE &&
> + pts_time >= ost->forced_keyframes_expr_const_values[FKF_NEXT_T]) {
> + ost->forced_keyframes_expr_const_values[FKF_N] += 1;
> + ost->forced_keyframes_expr_const_values[FKF_PREV_T] = pts_time;
> + ost->forced_keyframes_expr_const_values[FKF_NEXT_T] =
> + av_expr_eval(ost->forced_keyframes_pexpr, ost->forced_keyframes_expr_const_values, NULL);
> + forced_keyframe = 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);
> @@ -2226,9 +2251,24 @@ static int transcode_init(void)
> codec->bits_per_raw_sample = frame_bits_per_raw_sample;
> }
>
> + if (ost->forced_keyframes && ost->forced_keyframes_expr) {
> + av_log(NULL, AV_LOG_ERROR,
> + "forced_keyframes and forced_keyframes_expr are incompatible, select just one\n");
> + return AVERROR(EINVAL);
> + }
> if (ost->forced_keyframes)
> parse_forced_key_frames(ost->forced_keyframes, ost,
> ost->st->codec);
> + if (ost->forced_keyframes_expr) {
> + ret = av_expr_parse(&ost->forced_keyframes_pexpr, ost->forced_keyframes_expr,
> + forced_keyframes_const_names, NULL, NULL, NULL, NULL, 0, NULL);
> + if (ret < 0)
> + return ret;
> + ost->forced_keyframes_expr_const_values[FKF_N] = 0;
> + ost->forced_keyframes_expr_const_values[FKF_PREV_T] = NAN;
> + ost->forced_keyframes_expr_const_values[FKF_NEXT_T] =
> + av_expr_eval(ost->forced_keyframes_pexpr, ost->forced_keyframes_expr_const_values, NULL);
> + }
Possible alternate implementation: -force_key_frames expr:prev_t+5.
It has the advantage of not requiring all the code for new options, you just
have to add a test in parse_forced_key_frames(); that would make the code
much simpler I believe. And you do not have to worry about the user giving
incompatible options.
> break;
> case AVMEDIA_TYPE_SUBTITLE:
> codec->time_base = (AVRational){1, 1000};
> diff --git a/ffmpeg.h b/ffmpeg.h
> index afef6fb..12c563d 100644
> --- a/ffmpeg.h
> +++ b/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"
> @@ -139,6 +140,8 @@ typedef struct OptionsContext {
> int nb_qscale;
> SpecifierOpt *forced_key_frames;
> int nb_forced_key_frames;
> + SpecifierOpt *forced_key_frames_expr;
> + int nb_forced_key_frames_expr;
> SpecifierOpt *force_fps;
> int nb_force_fps;
> SpecifierOpt *frame_aspect_ratios;
> @@ -284,6 +287,15 @@ typedef struct InputFile {
> #endif
> } InputFile;
>
> +enum forced_keyframes_const {
> + FKF_N,
> + FKF_PREV_T,
> + FKF_NEXT_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 */
> @@ -315,6 +327,9 @@ typedef struct OutputStream {
> int forced_kf_count;
> int forced_kf_index;
> char *forced_keyframes;
> + char *forced_keyframes_expr;
> + 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 */
> diff --git a/ffmpeg_opt.c b/ffmpeg_opt.c
> index c846a10..4b6eda0 100644
> --- a/ffmpeg_opt.c
> +++ b/ffmpeg_opt.c
> @@ -1174,6 +1174,10 @@ static OutputStream *new_video_stream(OptionsContext *o, AVFormatContext *oc, in
> if (ost->forced_keyframes)
> ost->forced_keyframes = av_strdup(ost->forced_keyframes);
>
> + MATCH_PER_STREAM_OPT(forced_key_frames_expr, str, ost->forced_keyframes_expr, oc, st);
> + if (ost->forced_keyframes_expr)
> + ost->forced_keyframes_expr = av_strdup(ost->forced_keyframes_expr);
> +
> MATCH_PER_STREAM_OPT(force_fps, i, ost->force_fps, oc, st);
>
> ost->top_field_first = -1;
> @@ -2451,6 +2455,9 @@ const OptionDef options[] = {
> { "force_key_frames", OPT_VIDEO | OPT_STRING | HAS_ARG | OPT_EXPERT | OPT_SPEC,
> { .off = OFFSET(forced_key_frames) },
> "force key frames at specified timestamps", "timestamps" },
> + { "force_key_frames_expr", OPT_VIDEO | OPT_STRING | HAS_ARG | OPT_EXPERT | OPT_SPEC,
> + { .off = OFFSET(forced_key_frames_expr) },
> + "force key frames when the given expression is true", "expression" },
> { "b", OPT_VIDEO | HAS_ARG | OPT_PERFILE, { .func_arg = opt_bitrate },
> "video bitrate (please use -b:v)", "bitrate" },
Regards,
--
Nicolas George
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