[FFmpeg-devel] [PATCH] avformat/hls: Fixes overwriting existing #EXT-X-PROGRAM-DATE-TIME value in HLS playlist
Steven Liu
lq at chinaffmpeg.org
Wed Nov 25 14:01:17 EET 2020
> 2020年11月25日 下午7:49，Vignesh Ravichandran <vignesh.ravichandran02 at gmail.com> 写道：
>
> We could add a simple check like below to prevent it:
>
> if (sscanf(ptr, "%d-%d-%dT%d:%d:%d.%lf", &y, &M, &d, &h, &m, &s, &ms) != 7)
> {
> ret = AVERROR_INVALIDDATA;
> goto fail;
> }
>
> Please let me know.
Not sure this is better way, what about validate the string of the "#EXT-X-PROGRAM-DATE-TIME” values？
>
>
> Thanks,
> Vignesh
>
> On Wed, Nov 25, 2020 at 11:29 AM Steven Liu <lq at chinaffmpeg.org> wrote:
>
>>
>>
>>> 2020年11月25日 下午1:16，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 | 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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Thanks
Steven Liu
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