> 在 2018年1月28日，上午9:09，Brendan McGrath <red...@redmandi.dyndns.org> 写道：
>
> 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]
>
will apply it
> 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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