[FFmpeg-devel] [PATCH 2/3] avformat/mpegts: cache PID discard values

[Marton Balint]

On Fri, 25 Jan 2019, Michael Niedermayer wrote:

> On Thu, Jan 24, 2019 at 09:38:00PM +0100, Marton Balint wrote:
>> discard_pid can be quite expensive, so let's cache it and recalculate it on
>> every packet start.
>>
>> ffmpeg -y -i samples/MPEG-VOB/sdtv/RAI.ts -c copy -map 0:v:0 -map 0:a:0 -f mpegts /dev/null
>>
>> Before:
>>    1685 decicycles in handle_packet,  523483 runs,    805 skips
>>
>> After:
>>     883 decicycles in handle_packet,  523505 runs,    783 skips
>>
>> Signed-off-by: Marton Balint <cus at passwd.hu>
>> ---
>>  libavformat/mpegts.c | 7 +++++--
>>  1 file changed, 5 insertions(+), 2 deletions(-)
>>
>> diff --git a/libavformat/mpegts.c b/libavformat/mpegts.c
>> index 300db110d4..b04fd7b4f4 100644
>> --- a/libavformat/mpegts.c
>> +++ b/libavformat/mpegts.c
>> @@ -91,6 +91,7 @@ struct MpegTSFilter {
>>      int es_id;
>>      int last_cc; /* last cc code (-1 if first packet) */
>>      int64_t last_pcr;
>> +    int discard;
>>      enum MpegTSFilterType type;
>>      union {
>>          MpegTSPESFilter pes_filter;
>> @@ -2474,8 +2475,6 @@ static int handle_packet(MpegTSContext *ts, const uint8_t *packet)
>>      int64_t pos;
>>
>>      pid = AV_RB16(packet + 1) & 0x1fff;
>> -    if (pid && discard_pid(ts, pid))
>> -        return 0;
>>      is_start = packet[1] & 0x40;
>>      tss = ts->pids[pid];
>>      if (ts->auto_guess && !tss && is_start) {
>> @@ -2484,6 +2483,10 @@ static int handle_packet(MpegTSContext *ts, const uint8_t *packet)
>>      }
>>      if (!tss)
>>          return 0;
>> +    if (is_start)
>> +        tss->discard = discard_pid(ts, pid);
>> +    if (tss->discard)
>> +        return 0;
>
> this is moving the discard check over the auto_guess /add_pes_stream()
> have you checked or know that this is ok ?
> its not immedeatly obviouls (to me) why this would have no side effects

As far as I see that code is used to add streams which are not part of 
the detected programs. Therefore program discards should not concern them.

Regards,
Marton