Just making sure this patch hasn't been overlooked.
To better explain the existing issue - the value of 'pls->first_seq_no'
comes from the 'startNumber' attribute of the 'SegmentTemplate' element.
The 'pls->timelines' array represents the elements within the
'SegmentTimeline' element.
So for this example:
<SegmentTemplate timescale="48000"
initialization="init-stream$RepresentationID$.m4s"
media="chunk-stream$RepresentationID$-$Number%05d$.m4s" startNumber="7">
<SegmentTimeline>
<S t="2196480" d="480256" r="1" />
</SegmentTimeline>
</SegmentTemplate>
'pls->first_seq_no' will be 7 but the 'pls->timelines' array will only
have the one element - hence:
pls->timelines[pls->first_seq_no]
causes a segfault.
This patch removes the use of 'pls->first_seq_no' within the
'pls->timelines' array
On 20/01/18 18:07, Brendan McGrath wrote:
If first_seq_no is not within the bounds of timelines then a segfault
will occur.
This patch removes the use of first_seq_no within the timelines array
It also adds first_seq_no to the value returned by
calc_next_seg_no_from_timelines
(which allows for different values of 'startNumber')
Signed-off-by: Brendan McGrath <red...@redmandi.dyndns.org>
---
This can be reproduced by creating a dash file with the following command:
ffmpeg -i in.ts -f dash -window_size 2 out.mpd
and then after about 10 seconds run ffprobe against it.
The SegementTemplatei of out.mpd will look something like this:
<SegmentTemplate timescale="48000" initialization="init-stream$RepresentationID$.m4s"
media="chunk-stream$RepresentationID$-$Number%05d$.m4s" startNumber="7">
<SegmentTimeline>
<S t="2196480" d="480256" r="1" />
</SegmentTimeline>
</SegmentTemplate>
So the code was trying to access the 7th element within the timeline
array (which only had one element).
The patch doesn't worry about checking for a negative value after deducting the
60
seconds as calc_next_seg_no_from_timelines accepts a signed int and works
correctly with
negative values.
libavformat/dashdec.c | 11 ++++-------
1 file changed, 4 insertions(+), 7 deletions(-)
diff --git a/libavformat/dashdec.c b/libavformat/dashdec.c
index 2492f1d..cdb7ba5 100644
--- a/libavformat/dashdec.c
+++ b/libavformat/dashdec.c
@@ -1083,15 +1083,12 @@ static int64_t calc_cur_seg_no(AVFormatContext *s,
struct representation *pls)
if (pls->n_fragments) {
num = pls->first_seq_no;
} else if (pls->n_timelines) {
- start_time_offset = get_segment_start_time_based_on_timeline(pls,
0xFFFFFFFF) - pls->timelines[pls->first_seq_no]->starttime; // total duration
of playlist
- if (start_time_offset < 60 * pls->fragment_timescale)
- start_time_offset = 0;
- else
- start_time_offset = start_time_offset - 60 *
pls->fragment_timescale;
-
- num = calc_next_seg_no_from_timelines(pls,
pls->timelines[pls->first_seq_no]->starttime + start_time_offset);
+ start_time_offset = get_segment_start_time_based_on_timeline(pls,
0xFFFFFFFF) - 60 * pls->fragment_timescale; // 60 seconds before end
+ num = calc_next_seg_no_from_timelines(pls, start_time_offset);
if (num == -1)
num = pls->first_seq_no;
+ else
+ num += pls->first_seq_no;
} else if (pls->fragment_duration){
if (pls->presentation_timeoffset) {
num = pls->presentation_timeoffset * pls->fragment_timescale /
pls->fragment_duration;
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