On Sun, Jul 18, 2021 at 5:26 PM Gyan Doshi <ffm...@gyani.pro> wrote: > > > > On 2021-07-18 13:35, Linjie Fu wrote: > > On Sun, Jul 18, 2021 at 1:21 PM Gyan Doshi <ffm...@gyani.pro> wrote: > >> > >> > >> On 2021-07-18 10:42, Linjie Fu wrote: > >>> Hi Gyan, > >>> On Sun, Jul 18, 2021 at 12:24 PM Gyan Doshi <ffm...@gyani.pro> wrote: > >>>> > >>>> On 2021-07-18 09:32, Linjie Fu wrote: > >>>>> On Wed, Jul 7, 2021 at 9:42 AM Linjie Fu <linjie.justin...@gmail.com> > >>>>> wrote: > >>>>>> On Sun, Jul 4, 2021 at 10:50 PM Linjie Fu <fulin...@zju.edu.cn> wrote: > >>>>>>> From: Linjie Fu <linjie.justin...@gmail.com> > >>>>>>> > >>>>>>> Skip the logic of frame rate emulation until the input reaches the > >>>>>>> specified start time. > >>>>>>> > >>>>>>> Test CMD: > >>>>>>> $ffmpeg -re -ss 30 -i input.mp4 -pix_fmt yuv420p -f sdl2 - > >>>>>>> > >>>>>>> Before the patch: > >>>>>>> first time to got frame, it takes 257305 us > >>>>>>> After this patch: > >>>>>>> first time to got frame, it takes 48879 us > >>>>>>> > >>>>>>> Signed-off-by: Linjie Fu <linjie.justin...@gmail.com> > >>>>>>> --- > >>>>>>> [v2]: fixed the mixed declaration and code warning > >>>>>>> Calculate the time to get the first frame: > >>>>>>> https://github.com/fulinjie/ffmpeg/commit/2aa4762e1e65709997b1ab9dd596332244db80ed > >>>>>>> fftools/ffmpeg.c | 8 ++++++-- > >>>>>>> 1 file changed, 6 insertions(+), 2 deletions(-) > >>>>>>> > >>>>>>> diff --git a/fftools/ffmpeg.c b/fftools/ffmpeg.c > >>>>>>> index e97d879cb3..c8849e4250 100644 > >>>>>>> --- a/fftools/ffmpeg.c > >>>>>>> +++ b/fftools/ffmpeg.c > >>>>>>> @@ -4221,10 +4221,14 @@ static int get_input_packet(InputFile *f, > >>>>>>> AVPacket **pkt) > >>>>>>> { > >>>>>>> if (f->rate_emu) { > >>>>>>> int i; > >>>>>>> + int64_t pts; > >>>>>>> + int64_t now; > >>>>>>> for (i = 0; i < f->nb_streams; i++) { > >>>>>>> InputStream *ist = input_streams[f->ist_index + i]; > >>>>>>> - int64_t pts = av_rescale(ist->dts, 1000000, > >>>>>>> AV_TIME_BASE); > >>>>>>> - int64_t now = av_gettime_relative() - ist->start; > >>>>>>> + if (!ist->got_output) > >>>>>>> + continue; > >>>>>>> + pts = av_rescale(ist->dts, 1000000, AV_TIME_BASE); > >>>>>>> + now = av_gettime_relative() - ist->start; > >>>>>>> if (pts > now) > >>>>>>> return AVERROR(EAGAIN); > >>>>>>> } > >>>>>>> -- > >>>>>>> 2.31.1 > >>>>>> ping, thx. > >>>>>> > >>>>> Another ping, thx. > >>>> I pushed changes to this code yesterday. I don't think it's required > >>>> anymore, but do test. > >>>> > >>> Thanks for the review, tested after applying the readrate patch, I'm > >>> afraid that it's not identical as hope, > >>> since ist->nb_packets would increase no matter input stream got output or > >>> not: > >>> > >>> (lldb) p ist->nb_packets > >>> (uint64_t) $4 = 1 > >>> > >>> (lldb) p ist->got_output > >>> (int) $5 = 0 > >>> > >>> Hence we still need to add the check for ist->got_output, or replace > >>> the ist->nb_packets. > >> No, test the speed, not the parity of got_output. got_output is only > >> incremented when the stream is decoded. > > The time interval consumed to get the first frame is tested as well, > > it's not speeded up: > > First time to get the frame, it takes 257395 us. > > After adding the check for got_output in decoding scenery, this would > > reduce to 48792 us. > > > > Hence it doesn't reduce the latency under decode scenery. > > > >> Won't work with streamcopy. > > Got your point. > > > >> nb_packets is the correct check since it's incremented after the initial > >> packet is demuxed. > > IIRC, the initial packet is demuxed right after the first time we call > > get_input_packet()-> av_read_frame(), and nb_packets would increase. > > Hence, the check for ist->nb_packets would reduce the latency for > > demuxing the first packet, > > and won't help much if we use start_time like "-ss 30". Under the > > decoding scenery, we still > > need to wait until the pkt->pts specified time then demux the packet. > > > > If no objections, consider to change the check to: > > > > if (!ist->nb_packets || (!ist->got_output && ist->decoding_needed)) > > continue; > > > > to reduce the waiting time for: > > 1. demuxing the first packet (if any) > > 2. demuxing the packet before we got the first decoded output. > > Which sample file are you using, and how do I reproduce the timings? > It could be reproduced with a random input file (if long enough), and the time calculating method I used previously (needs to rebase a little bit for now): https://github.com/fulinjie/ffmpeg/commit/2aa4762e1e65709997b1ab9dd596332244db80ed
CMD: $ffmpeg -re -ss 30 -i input.mp4 -pix_fmt yuv420p -f sdl2 - or $ffmpeg -re -ss 30 -i input.mp4 -f null - - linjie _______________________________________________ ffmpeg-devel mailing list ffmpeg-devel@ffmpeg.org https://ffmpeg.org/mailman/listinfo/ffmpeg-devel To unsubscribe, visit link above, or email ffmpeg-devel-requ...@ffmpeg.org with subject "unsubscribe".
