[vlc-devel] [PATCH 2/3] demux: avformat: fix negative PTS/DTS
Zhao Zhili
quinkblack at foxmail.com
Thu Aug 31 15:32:42 CEST 2017
On 2017年08月31日 18:44, Rémi Denis-Courmont wrote:
> Le 31 août 2017 12:24:03 GMT+02:00, Zhao Zhili <quinkblack at foxmail.com> a écrit :
>> On 2017年08月31日 17:58, Francois Cartegnie wrote:
>>> Le 31/08/2017 à 08:48, Zhao Zhili a écrit :
>>>> ---
>>>> modules/demux/avformat/demux.c | 41
>>>> +++++++++++++++++++++++++++++------------
>>>> 1 file changed, 29 insertions(+), 12 deletions(-)
>>>>
>>> If the timestamps are negative from the start, I don't see
>>> why the issue should be on the API user side.
>>>
>>> But, this seems the same as last February discussion around
>>> "mux/avformat: normalize pts and dts in AVPacket"
>>> which had regressions.
>>>
>>> https://trac.videolan.org/vlc/ticket/17988
>>>
>> I'm trying to fix a case like this:
>>
>> original_start_time = 1000 * 1000 us;
>> original_pts = 1000 * 1000 us;
>> original_dts = 960 * 1000 us;
>>
>> new_pts = original_pts - original_start_time + VLC_TS_0 = 1 us;
>> new_dts = original_dts - original_start_time + VLC_TS_0 = -39999 us;
>>
>> So it's the difference between PTS and DTS lead to the issue.
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> Negative timestamps can occur in some legal corner cases. There are no systematic ways to avoid them. You really shouldn't even try.
>
> Just make sure than 0 is not a special value. There is VLC_TS_INVALID for that.
How about this:
1. If the original PTS and DTS output from libavformat is negative, do
nothing.
2. Otherwise, which most likely means the negative PTS and DTS is produced
by shift, then shift start_time to produced positive timestamps.
3. PTS/DTS wrap can lead to negative timestamps too, which is harder to
handle.
Don't distinguish this case from case 2.
A new patch is attached.
---
modules/demux/avformat/demux.c | 41
+++++++++++++++++++++++++++++------------
1 file changed, 29 insertions(+), 12 deletions(-)
diff --git a/modules/demux/avformat/demux.c b/modules/demux/avformat/demux.c
index 3c4c112..3bb7813 100644
--- a/modules/demux/avformat/demux.c
+++ b/modules/demux/avformat/demux.c
@@ -72,6 +72,7 @@ struct demux_sys_t
/* Only one title with seekpoints possible atm. */
input_title_t *p_title;
+ int64_t i_start_time;
};
#define AVFORMAT_IOBUFFER_SIZE 32768 /* FIXME */
@@ -274,6 +275,7 @@ int OpenDemux( vlc_object_t *p_this )
p_sys->i_ssa_order = 0;
TAB_INIT( p_sys->i_attachments, p_sys->attachments);
p_sys->p_title = NULL;
+ p_sys->i_start_time = 0;
/* Create I/O wrapper */
unsigned char * p_io_buffer = av_malloc( AVFORMAT_IOBUFFER_SIZE );
@@ -623,8 +625,11 @@ int OpenDemux( vlc_object_t *p_this )
}
p_sys->tk_pcr = xcalloc( p_sys->i_tk, sizeof(*p_sys->tk_pcr) );
- if( p_sys->ic->start_time != (int64_t)AV_NOPTS_VALUE )
- i_start_time = p_sys->ic->start_time * 1000000 / AV_TIME_BASE;
+ if( p_sys->ic->start_time != (int64_t)AV_NOPTS_VALUE ) {
+ lldiv_t q = lldiv( p_sys->ic->start_time, AV_TIME_BASE);
+ i_start_time = q.quot * CLOCK_FREQ + q.rem * CLOCK_FREQ /
AV_TIME_BASE;
+ p_sys->i_start_time = i_start_time;
+ }
msg_Dbg( p_demux, "AVFormat(%s %s) supported stream",
AVPROVIDER(LIBAVFORMAT), LIBAVFORMAT_IDENT );
msg_Dbg( p_demux, " - format = %s (%s)",
@@ -701,7 +706,6 @@ static int Demux( demux_t *p_demux )
demux_sys_t *p_sys = p_demux->p_sys;
AVPacket pkt;
block_t *p_frame;
- int64_t i_start_time;
/* Read a frame */
int i_av_ret = av_read_frame( p_sys->ic, &pkt );
@@ -749,13 +753,6 @@ static int Demux( demux_t *p_demux )
/* Used to avoid timestamps overlow */
lldiv_t q;
- if( p_sys->ic->start_time != (int64_t)AV_NOPTS_VALUE )
- {
- q = lldiv( p_sys->ic->start_time, AV_TIME_BASE);
- i_start_time = q.quot * CLOCK_FREQ + q.rem * CLOCK_FREQ /
AV_TIME_BASE;
- }
- else
- i_start_time = 0;
if( pkt.dts == (int64_t)AV_NOPTS_VALUE )
p_frame->i_dts = VLC_TS_INVALID;
@@ -765,7 +762,16 @@ static int Demux( demux_t *p_demux )
p_frame->i_dts = q.quot * CLOCK_FREQ *
p_stream->time_base.num + q.rem * CLOCK_FREQ *
p_stream->time_base.num /
- p_stream->time_base.den - i_start_time + VLC_TS_0;
+ p_stream->time_base.den - p_sys->i_start_time + VLC_TS_0;
+ if( p_frame->i_dts < VLC_TS_0 && pkt.dts >= 0 )
+ {
+ int64_t i_start_time = p_sys->i_start_time;
+ p_sys->i_start_time -= VLC_TS_0 - p_frame->i_dts;
+ msg_Dbg( p_demux, "adjust start time from %" PRId64 " to %"
PRId64
+ " since DTS < 0", i_start_time, p_sys->i_start_time );
+
+ p_frame->i_dts = VLC_TS_0;
+ }
}
if( pkt.pts == (int64_t)AV_NOPTS_VALUE )
@@ -776,7 +782,18 @@ static int Demux( demux_t *p_demux )
p_frame->i_pts = q.quot * CLOCK_FREQ *
p_stream->time_base.num + q.rem * CLOCK_FREQ *
p_stream->time_base.num /
- p_stream->time_base.den - i_start_time + VLC_TS_0;
+ p_stream->time_base.den - p_sys->i_start_time + VLC_TS_0;
+ if( p_frame->i_pts < VLC_TS_0 && pkt.pts >= 0 )
+ {
+ int64_t i_start_time = p_sys->i_start_time;
+ p_sys->i_start_time -= VLC_TS_0 - p_frame->i_pts;
+ msg_Dbg( p_demux, "adjust start time from %" PRId64 " to %"
PRId64
+ " since PTS < 0", i_start_time, p_sys->i_start_time );
+
+ p_frame->i_pts = VLC_TS_0;
+ if( p_frame->i_dts != VLC_TS_INVALID )
+ p_frame->i_dts += VLC_TS_0 - p_frame->i_pts;
+ }
}
if( pkt.duration > 0 && p_frame->i_length <= 0 )
p_frame->i_length = pkt.duration * CLOCK_FREQ *
--
2.7.4
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