Re: [FFmpeg-devel] [PATCH v1] avformat/hlsenc: fix hls_time not respected

[Ingo Oppermann <ingo@datarhei.com>]

> On 24 Jan 2025, at 16:30, Gyan Doshi <ffmpeg@gyani.pro> wrote:
> 
> 
> 
> On 2025-01-24 05:29 pm, Ingo Oppermann wrote:
>> This fixes the criterion when to split the segments based on the elapsed time
>> for the current segment instead of using the theoretical elapsed time since
>> start based on hls_time and the number of written segments.
>> 
>> hls_time is used to define the minimum 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. 40 seconds.
>> After that, key frames will come every second. This will result in segments
>> that are first 10 seconds, then 1 second for some time and later 2 seconds as
>> expected.
> 
> Better to make it flexible like how the segment muxer does it, by having an optional minimum segment duration parameter. Then it's upto the user.
> See d39b34123d.

According to the documentation "hls_time" is already supposed to be the minimum duration of a segment: "Segment will be cut on the next key frame after this time has passed." (https://ffmpeg.org/ffmpeg-formats.html#Options-26). It does this under normal circumstances, e.g.

ffmpeg -t 30 -f lavfi -i testsrc2 -codec:v libx264 -g 25 -f hls -hls_time 2 -hls_list_size 0 split.m3u8

Every segment is 2 seconds even though the GOP size 1 second.


> 
> Also Patchwork warns about the line length in the commit message. Should be <=72

Will fix this in the following version of the patch.

> 
> Regards,
> Gyan
> 
> 
>> 
>> How to reproduce:
>> ffmpeg -t 40 -f lavfi -i testsrc2=s=1280x720:r=25 -codec:v libx264 -g 250 part1.mp4
>> ffmpeg -t 40 -f lavfi -i testsrc2=s=1280x720:r=25 -codec:v libx264 -g 25 part2.mp4
>> echo "file part1.mp4\nfile part2.mp4" > list.txt
>> ffmpeg -f concat -i list.txt -codec copy part.mp4
>> ffmpeg -i part.mp4 -codec copy -f hls -hls_time 2 -hls_list_size 0 -hls_segment_filename 'part_%d.ts' part.m3u8
>> cat part.m3u8
>> 
>> Signed-off-by: Ingo Oppermann <ingo@datarhei.com>
>> ---
>>  libavformat/hlsenc.c | 12 +++---------
>>  1 file changed, 3 insertions(+), 9 deletions(-)
>> 
>> diff --git a/libavformat/hlsenc.c b/libavformat/hlsenc.c
>> index 6148685f40..2c5d60500d 100644
>> --- a/libavformat/hlsenc.c
>> +++ b/libavformat/hlsenc.c
>> @@ -2474,7 +2474,6 @@ 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;
>>      int is_ref_pkt = 1;
>>      int ret = 0, can_split = 1, i, j;
>>      int stream_index = 0;
>> @@ -2512,14 +2511,9 @@ static int hls_write_packet(AVFormatContext *s, AVPacket *pkt)
>>          return AVERROR(ENOMEM);
>>      }
>>  -    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;
>> +        /* reset hls->recording_time at end of the init hls list */
>>          hls->recording_time = hls->time;
>> -        end_pts = init_list_dur + after_init_list_dur ;
>>      }
>>        if (vs->start_pts == AV_NOPTS_VALUE) {
>> @@ -2560,8 +2554,8 @@ 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) {
>> +    if (vs->packets_written && can_split && av_compare_ts(pkt->pts - vs->end_pts, st->time_base,
>> +                                                          hls->recording_time, AV_TIME_BASE_Q) >= 0) {
>>          int64_t new_start_pos;
>>          int byterange_mode = (hls->flags & HLS_SINGLE_FILE) || (hls->max_seg_size > 0);
>>          double cur_duration;
>> 
>> base-commit: e20ee9f9aec94f8cea1bf4fd8ed3fb096fb205e5
> 
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