Re: [FFmpeg-devel] [PATCH v2] avformat/hlsenc: add hls_min_time to guarantee minimal segment duration

[Steven Liu <lingjiujianke@gmail.com>]

Ingo Oppermann <ingo@datarhei.com> 于2025年6月5日周四 15:24写道：
>
> The current implementation of the hls_time might produce segments
> with shorter duration in some cases which is not as expected. With the
> hls_min_time option the minimal segment duration will be guaranteed by
> splitting by the next keyframe after the desired duration of the
> segment has been reached.
>
> Instead of changing the current behaviour of hls_time which might
> break existing workflows, the new option hls_min_time will override
> hls_time and guarantee the minimal segment duration.
>
> hls_time is supposed to define the minimal length of a segment,
> however this is not respected in all cases when a stream has variable
> GOP sizes.
>
> Imagine a stream starts with a key frame every 10 seconds for
> e.g. 30 seconds. After that, key frames will come every second. This
> will result in segments that are first 10 seconds (as expected), then
> 1 second for some time (not as expected) and later 2 seconds (as
> expected).
>
> How to reproduce:
> ffmpeg -t 30 -f lavfi -i testsrc2 -codec:v libx264 -g 250 part1.mp4
> ffmpeg -t 30 -f lavfi -i testsrc2 -codec:v libx264 -g 25 part2.mp4
> echo "file part1.mp4\nfile part2.mp4" > list.txt
> ffmpeg -f concat -i list.txt -codec copy \
>     -f hls -hls_time 2 -hls_list_size 0 parts.m3u8
> cat parts.m3u8
>
> v2 changes:
> Adjusting wording in commit message as suggested by Steven Liu.
>
> Signed-off-by: Ingo Oppermann <ingo@datarhei.com>
> ---
>  doc/muxers.texi      |  7 +++++++
>  libavformat/hlsenc.c | 27 ++++++++++++++++++++-------
>  2 files changed, 27 insertions(+), 7 deletions(-)
>
> diff --git a/doc/muxers.texi b/doc/muxers.texi
> index 30c95c3d34..082647bd9d 100644
> --- a/doc/muxers.texi
> +++ b/doc/muxers.texi
> @@ -1929,6 +1929,13 @@ Set the target segment length. Default value is 2.
>  see @ref{time duration syntax,,the Time duration section in the ffmpeg-utils(1) manual,ffmpeg-utils}.
>  Segment will be cut on the next key frame after this time has passed.
>
> +@item hls_min_time @var{duration}
> +Set the minimum target segment length. Default value is 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 at least this long and will be cut at the following key frame. If set, it will override @option{hls_time}.
> +
>  @item hls_list_size @var{size}
>  Set the maximum number of playlist entries. If set to 0 the list file
>  will contain all the segments. Default value is 5.
> diff --git a/libavformat/hlsenc.c b/libavformat/hlsenc.c
> index a93d35ab75..082229467f 100644
> --- a/libavformat/hlsenc.c
> +++ b/libavformat/hlsenc.c
> @@ -204,6 +204,7 @@ typedef struct HLSContext {
>      uint32_t start_sequence_source_type;  // enum StartSequenceSourceType
>
>      int64_t time;          // Set by a private option.
> +    int64_t min_time;      // Set by a private option.
>      int64_t init_time;     // Set by a private option.
>      int max_nb_segments;   // Set by a private option.
>      int hls_delete_threshold; // Set by a private option.
> @@ -2506,7 +2507,7 @@ static int hls_write_packet(AVFormatContext *s, AVPacket *pkt)
>      HLSContext *hls = s->priv_data;
>      AVFormatContext *oc = NULL;
>      AVStream *st = s->streams[pkt->stream_index];
> -    int64_t end_pts = 0;
> +    int64_t end_pts = 0, current_pts;
>      int is_ref_pkt = 1;
>      int ret = 0, can_split = 1, i, j;
>      int stream_index = 0;
> @@ -2547,11 +2548,16 @@ static int hls_write_packet(AVFormatContext *s, AVPacket *pkt)
>      end_pts = hls->recording_time * vs->number;
>
>      if (vs->sequence - vs->nb_entries > hls->start_sequence && hls->init_time > 0) {
> -        /* reset end_pts, hls->recording_time at end of the init hls list */
> -        int64_t init_list_dur = hls->init_time * vs->nb_entries;
> -        int64_t after_init_list_dur = (vs->sequence - hls->start_sequence - vs->nb_entries) * hls->time;
> -        hls->recording_time = hls->time;
> -        end_pts = init_list_dur + after_init_list_dur ;
> +        if (hls->min_time > 0) {
> +            hls->recording_time = hls->min_time;
> +            hls->init_time = 0;
> +        } else {
> +            /* reset end_pts, hls->recording_time at end of the init hls list */
> +            int64_t init_list_dur = hls->init_time * vs->nb_entries;
> +            int64_t after_init_list_dur = (vs->sequence - hls->start_sequence - vs->nb_entries) * hls->time;
> +            hls->recording_time = hls->time;
> +            end_pts = init_list_dur + after_init_list_dur;
> +        }
>      }
>
>      if (vs->start_pts == AV_NOPTS_VALUE) {
> @@ -2591,8 +2597,14 @@ static int hls_write_packet(AVFormatContext *s, AVPacket *pkt)
>          }
>      }
>
> +    current_pts = pkt->pts - vs->start_pts;
> +    if (hls->min_time > 0 && hls->init_time == 0) {
> +        current_pts = pkt->pts - vs->end_pts;
> +        end_pts = hls->min_time;
> +    }
> +
>      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,
> +    if (vs->packets_written && can_split && av_compare_ts(current_pts, st->time_base,
>                                                            end_pts, AV_TIME_BASE_Q) >= 0) {
>          int64_t new_start_pos;
>          int byterange_mode = (hls->flags & HLS_SINGLE_FILE) || (hls->max_seg_size > 0);
> @@ -3214,6 +3226,7 @@ static int hls_init(AVFormatContext *s)
>  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_min_time",  "set minimum segment length",              OFFSET(min_time),      AV_OPT_TYPE_DURATION, {.i64 = 0},       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_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},
>
> base-commit: a4c1a5b08409cdfeb8e7f92c7fd443c8ff42e00d
> --
> 2.39.5 (Apple Git-154)
>
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looks ok to me, this need a fate test case.


Thanks
Steven
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