On Wed, 20 May 2020, Limin Wang wrote:
On Wed, May 20, 2020 at 08:26:37AM +0200, Marton Balint wrote:
On Wed, 20 May 2020, lance.lmw...@gmail.com wrote:
>On Tue, May 19, 2020 at 09:06:59PM +0200, Marton Balint wrote:
>>pos47_full is not updated for every packet, and for unseekable inputs the
>>resync logic might simply skip some 0x47 sync bytes. In order to detect these
>>let's check for modulo instead of exact value.
>
>Before modifying and returning directly, I considered whether pos
>is a multiple of raw_packet_size, by the debug information, it's
>not true.
Not always, because sometimes there are 0x47 sync bytes in the
packet payload as well. But we siply ignore that case because of the
return later originated from your patch. Checking for modulo allows
faster detection and it also allows detection when UDP packets
contain a single MPEGTS packet.
>Also it's possible
>for the pos of two sync byte > 188/192/204 * n. If that's true, it's not
correct
>to look it as stats hit by the modulo logic.
I don't understand what you mean here.
Let me give one example, the size is 192*2, but the second 192 isn't start by
0x47
sync byte, checking with modulo will not correct for the case
The mpegts demuxer can only detect 188, 192, or 204 byte packet sizes.
Arbitrary sizes (like 2*192) is simply not supported, so we don't have to
detect it.
Regards,
Marton
Regards,
Marton
>
>>
>>Also skip unrecognized sync byte distances instead of considering them as a
>>failure of detection. It only delays the detection of the new packet size.
>>
>>Also note that AVIO only buffers a single packet (for UDP/mpegts, that usually
>>means 1316 bytes), so among every ten consecutive 188-byte MPEGTS packets
there
>>will always be a seek failure, and that caused the old code to not find the
188
>>byte pattern across 10 consecutive packets.
>>
>>Signed-off-by: Marton Balint <c...@passwd.hu>
>>---
>> libavformat/mpegts.c | 8 +++++---
>> 1 file changed, 5 insertions(+), 3 deletions(-)
>>
>>diff --git a/libavformat/mpegts.c b/libavformat/mpegts.c
>>index a065c61c40..f2b2c05d86 100644
>>--- a/libavformat/mpegts.c
>>+++ b/libavformat/mpegts.c
>>@@ -2846,12 +2846,14 @@ static void reanalyze(MpegTSContext *ts) {
>> if (pos < 0)
>> return;
>> pos -= ts->pos47_full;
>>- if (pos == TS_PACKET_SIZE) {
>>+ if (pos % TS_PACKET_SIZE == 0) {
>> ts->size_stat[0] ++;
>>- } else if (pos == TS_DVHS_PACKET_SIZE) {
>>+ } if (pos % TS_DVHS_PACKET_SIZE == 0) {
>> ts->size_stat[1] ++;
>>- } else if (pos == TS_FEC_PACKET_SIZE) {
>>+ } if (pos % TS_FEC_PACKET_SIZE == 0) {
>> ts->size_stat[2] ++;
>>+ } else {
>>+ return;
>> }
>>
>> ts->size_stat_count ++;
>>--
>>2.26.1
>>
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>
>--
>Thanks,
>Limin Wang
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>
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--
Thanks,
Limin Wang
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