> 2020年11月25日 下午1:16，Vignesh Ravichandran <[email protected]> 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 <[email protected]>
> ---
> libavformat/hlsenc.c | 35 +++++++++++++++++++++++++++++++----
> 1 file changed, 31 insertions(+), 4 deletions(-)
>
> diff --git a/libavformat/hlsenc.c b/libavformat/hlsenc.c
> index cbfd8f7c0d..030a2d3b97 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 +1185,8 @@ static int parse_playlist(AVFormatContext *s, const
> char *url, VariantStream *vs
> char line[MAX_URL_SIZE];
> const char *ptr;
> const char *end;
> + int is_discont_detected = 0;
> + double discont_program_date_time = 0;
>
> if ((ret = ffio_open_whitelist(&in, url, AVIO_FLAG_READ,
> &s->interrupt_callback, NULL,
> @@ -1211,6 +1216,7 @@ static int parse_playlist(AVFormatContext *s, const
> char *url, VariantStream *vs
> } else if (av_strstart(line, "#EXT-X-DISCONTINUITY", &ptr)) {
> is_segment = 1;
> vs->discontinuity = 1;
> + is_discont_detected = 1;
> } else if (av_strstart(line, "#EXTINF:", &ptr)) {
> is_segment = 1;
> vs->duration = atof(ptr);
> @@ -1236,7 +1242,23 @@ 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) &&
> is_discont_detected) {
> + struct tm program_date_time;
> + int y,M,d,h,m,s;
> + double ms;
> + sscanf(ptr, "%d-%d-%dT%d:%d:%d.%lf", &y, &M, &d, &h, &m, &s,
> &ms);
What will happen if I modify the value of “EXT-X-PROGRAM-DATE-TIME” by hacker,
For example:
#EXT-X-PROGRAM-DATA-TIME: good-morning-ladies-and-gentlemen.
> +
> + 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);
> + is_discont_detected = 0;
> } 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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Thanks
Steven Liu
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