Re: [FFmpeg-devel] [PATCH] avformat/hlsenc: add hls_time_delta to cut segment at before hls_time

["\"zhilizhao(赵志立)\"" <quinkblack@foxmail.com>]

> On Mar 18, 2022, at 8:20 PM, Steven Liu <lq@chinaffmpeg.org> wrote:
> 
> From: Steven Liu <liuqi05@kuaishou.com>
> 
> There have some video stream usually cannot get precise duration,
> for example:
> 
> command:
> ffmpeg -i input.mp4 -c copy -copyts -f hls -hls_time 5 -hls_list_size 0 -hls_segment_type mpegts -t 20 a.m3u8
> 
> the first segment should split at 5.133333,
> because 5.133333 - 0.133333 is 5.0000,
> pkt->pts = [5.133333] vs->end_pts = 0.133333, flags = [1]
> but the second segment will cannot split at 10.133322,
> because 10.133322 - 5.133333 is 4.999989, it small than hls_time,

It doesn’t looks like an issue.

Firstly, user can specify a smaller ‘hls_time'. '-hls_time 4.9'
is the same as '-hls_time 5 -hls_time_delta 0.1', right?

Secondly, if user want to have precise segment durations, they
need to control the timestamp of input packets, with fixed FPS.

> pkt->pts = [10.133322] vs->end_pts = 5.133333, flags = [1]
> so add hls_time_delta for approximation value to hls_time.
> 
> Signed-off-by: Steven Liu <liuqi05@kuaishou.com>
> ---
> doc/muxers.texi      | 8 ++++++++
> libavformat/hlsenc.c | 4 +++-
> 2 files changed, 11 insertions(+), 1 deletion(-)
> 
> diff --git a/doc/muxers.texi b/doc/muxers.texi
> index 1af603b7f6..c91a7a9216 100644
> --- a/doc/muxers.texi
> +++ b/doc/muxers.texi
> @@ -778,6 +778,14 @@ Segment will be cut on the next key frame after this time has passed on the firs
> After the initial playlist is filled @command{ffmpeg} will cut segments
> at duration equal to @code{hls_time}
> 
> +@item hls_time_delta @var{duration}
> +Set approximation value used for the segment duration. Default value is @var{0}.
> +
> +@var{duration} must be a time duration specification,
> +see @ref{time duration syntax,,the Time duration section in the ffmpeg-utils(1) manual,ffmpeg-utils}.
> +
> +Segment will be cut on the key frame before @code{hls_time_delta} to @code{hls_time}.
> +
> @item hls_time @var{duration}
> Set the target segment length. Default value is 2.
> 
> diff --git a/libavformat/hlsenc.c b/libavformat/hlsenc.c
> index 14eb7c4530..56cde7dd70 100644
> --- a/libavformat/hlsenc.c
> +++ b/libavformat/hlsenc.c
> @@ -200,6 +200,7 @@ typedef struct HLSContext {
> 
>     int64_t time;          // Set by a private option.
>     int64_t init_time;     // Set by a private option.
> +    int64_t time_delta;
>     int max_nb_segments;   // Set by a private option.
>     int hls_delete_threshold; // Set by a private option.
>     uint32_t flags;        // enum HLSFlags
> @@ -2489,7 +2490,7 @@ static int hls_write_packet(AVFormatContext *s, AVPacket *pkt)
> 
>     can_split = can_split && (pkt->pts - vs->end_pts > 0);
>     if (vs->packets_written && can_split && av_compare_ts(pkt->pts - vs->start_pts, st->time_base,
> -                                                          end_pts, AV_TIME_BASE_Q) >= 0) {
> +                                                          end_pts - hls->time_delta, AV_TIME_BASE_Q) >= 0) {
>         int64_t new_start_pos;
>         int byterange_mode = (hls->flags & HLS_SINGLE_FILE) || (hls->max_seg_size > 0);
> 
> @@ -3101,6 +3102,7 @@ static const AVOption options[] = {
>     {"start_number",  "set first number in the sequence",        OFFSET(start_sequence),AV_OPT_TYPE_INT64,  {.i64 = 0},     0, INT64_MAX, E},
>     {"hls_time",      "set segment length",                      OFFSET(time),          AV_OPT_TYPE_DURATION, {.i64 = 2000000}, 0, INT64_MAX, E},
>     {"hls_init_time", "set segment length at init list",         OFFSET(init_time),     AV_OPT_TYPE_DURATION, {.i64 = 0},       0, INT64_MAX, E},
> +    {"hls_time_delta", "set approximation value used for the segment duration",         OFFSET(time_delta),     AV_OPT_TYPE_DURATION, {.i64 = 0},       0, INT64_MAX, E},
>     {"hls_list_size", "set maximum number of playlist entries",  OFFSET(max_nb_segments),    AV_OPT_TYPE_INT,    {.i64 = 5},     0, INT_MAX, E},
>     {"hls_delete_threshold", "set number of unreferenced segments to keep before deleting",  OFFSET(hls_delete_threshold),    AV_OPT_TYPE_INT,    {.i64 = 1},     1, INT_MAX, E},
> #if FF_HLS_TS_OPTIONS
> -- 
> 2.25.0
> 
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