[FFmpeg-devel] [PATCH] avformat/hls: Fixes overwriting existing #EXT-X-PROGRAM-DATE-TIME value in HLS playlist

[Steven Liu]

> 2020年12月1日 下午6:10，Vignesh Ravichandran <vignesh.ravichandran02 at gmail.com> 写道：
> 
> Bug ID: 8989
> 
> This is is due to the following behavior in the current code:
> 1. The initial_prog_date_time gets set to the current local time
> 2. The existing playlist (.m3u8) file gets parsed and the segments present are added to the variant stream
> 3. The new segment is created and added
> 4. The existing segments and the new segment are written to the playlist file. The initial_prog_date_time from point 1 is used for calculating "#EXT-X-PROGRAM-DATE-TIME" for the segments, which results in incorrect "#EXT-X-PROGRAM-DATE-TIME" values for existing segments
> 
> The following approach fixes this bug:
> 1. Add a new variable "discont_program_date_time" of type double to HLSSegment struct
> 2. Store the "EXT-X-PROGRAM-DATE-TIME" value from the existing segments in this variable
> 3. When writing to playlist file if "discont_program_date_time" is set, then use that value for "EXT-X-PROGRAM-DATE-TIME" else use the value present in vs->initial_prog_date_time
> 
> Signed-off-by: Vignesh Ravichandran <vignesh.ravichandran02 at gmail.com>
> ---
> libavformat/hlsenc.c | 33 ++++++++++++++++++++++++++++++---
> 1 file changed, 30 insertions(+), 3 deletions(-)
> 
> diff --git a/libavformat/hlsenc.c b/libavformat/hlsenc.c
> index cbfd8f7c0d..9bce374605 100644
> --- a/libavformat/hlsenc.c
> +++ b/libavformat/hlsenc.c
> @@ -88,6 +88,7 @@ typedef struct HLSSegment {
>     char iv_string[KEYSIZE*2 + 1];
> 
>     struct HLSSegment *next;
> +    double discont_program_date_time;
> } HLSSegment;
> 
> typedef enum HLSFlags {
> @@ -1124,6 +1125,7 @@ static int hls_append_segment(struct AVFormatContext *s, HLSContext *hls,
>     en->keyframe_size     = vs->video_keyframe_size;
>     en->next     = NULL;
>     en->discont  = 0;
> +    en->discont_program_date_time = 0;
> 
>     if (vs->discontinuity) {
>         en->discont = 1;
> @@ -1148,7 +1150,8 @@ static int hls_append_segment(struct AVFormatContext *s, HLSContext *hls,
> 
>     if (hls->max_nb_segments && vs->nb_entries >= hls->max_nb_segments) {
>         en = vs->segments;
> -        vs->initial_prog_date_time += en->duration;
> +        if (!en->next->discont_program_date_time && !en->discont_program_date_time)
> +            vs->initial_prog_date_time += en->duration;
>         vs->segments = en->next;
>         if (en && hls->flags & HLS_DELETE_SEGMENTS &&
> #if FF_API_HLS_WRAP
> @@ -1182,6 +1185,7 @@ static int parse_playlist(AVFormatContext *s, const char *url, VariantStream *vs
>     char line[MAX_URL_SIZE];
>     const char *ptr;
>     const char *end;
> +    double discont_program_date_time = 0;
> 
>     if ((ret = ffio_open_whitelist(&in, url, AVIO_FLAG_READ,
>                                    &s->interrupt_callback, NULL,
> @@ -1236,7 +1240,25 @@ static int parse_playlist(AVFormatContext *s, const char *url, VariantStream *vs
>                     av_strlcpy(vs->iv_string, ptr, sizeof(vs->iv_string));
>                 }
>             }
> +        } else if (av_strstart(line, "#EXT-X-PROGRAM-DATE-TIME:", &ptr)) {
> +            struct tm program_date_time;
> +            int y,M,d,h,m,s;
> +            double ms;
> +            if (sscanf(ptr, "%d-%d-%dT%d:%d:%d.%lf", &y, &M, &d, &h, &m, &s, &ms) != 7) {
> +                ret = AVERROR_INVALIDDATA;
> +                goto fail;
> +            }
> +
> +            program_date_time.tm_year = y - 1900;
> +            program_date_time.tm_mon = M - 1;
> +            program_date_time.tm_mday = d;
> +            program_date_time.tm_hour = h;
> +            program_date_time.tm_min = m;
> +            program_date_time.tm_sec = s;
> +            program_date_time.tm_isdst = -1;
> 
> +            discont_program_date_time = mktime(&program_date_time);
> +            discont_program_date_time += (double)(ms / 1000);
>         } else if (av_strstart(line, "#", NULL)) {
>             continue;
>         } else if (line[0]) {
> @@ -1250,8 +1272,9 @@ static int parse_playlist(AVFormatContext *s, const char *url, VariantStream *vs
>                 is_segment = 0;
>                 new_start_pos = avio_tell(vs->avf->pb);
>                 vs->size = new_start_pos - vs->start_pos;
> -                vs->initial_prog_date_time -= vs->duration; // this is a previously existing segment
>                 ret = hls_append_segment(s, hls, vs, vs->duration, vs->start_pos, vs->size);
> +                vs->last_segment->discont_program_date_time = discont_program_date_time;
> +                discont_program_date_time += vs->duration;
>                 if (ret < 0)
>                     goto fail;
>                 vs->start_pos = new_start_pos;
> @@ -1572,7 +1595,11 @@ static int hls_window(AVFormatContext *s, int last, VariantStream *vs)
>         ret = ff_hls_write_file_entry(byterange_mode ? hls->m3u8_out : vs->out, en->discont, byterange_mode,
>                                       en->duration, hls->flags & HLS_ROUND_DURATIONS,
>                                       en->size, en->pos, hls->baseurl,
> -                                      en->filename, prog_date_time_p, en->keyframe_size, en->keyframe_pos, hls->flags & HLS_I_FRAMES_ONLY);
> +                                      en->filename,
> +                                      en->discont_program_date_time ? &en->discont_program_date_time : prog_date_time_p,
> +                                      en->keyframe_size, en->keyframe_pos, hls->flags & HLS_I_FRAMES_ONLY);
> +        if (en->discont_program_date_time)
> +            en->discont_program_date_time -= en->duration;
>         if (ret < 0) {
>             av_log(s, AV_LOG_WARNING, "ff_hls_write_file_entry get error\n");
>         }
> -- 
> 2.24.2 (Apple Git-127)
> 
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LGTN

Will push if no objections. 

Thanks

Steven Liu