[Libav-user] how to set the time base ?

[Uğur Bozkaya]

> On Jun 14, 2016, at 5:28 PM, wucg <249165510 at qq.com> wrote:
> 
> Could anyone tell me how to set the time_base for  audio/video stream ?
> I hit my head agaist the wall for one thousand times, and still can't find a way to work it out!
> 
> (AVStream*)_audio_st->time_base = (AVRational ) { 1, _param.sampleRate };        // Not working
> (AVCodecContext*)_codec_ctx->time_base = (AVRational ) { 1, _param.sampleRate };        // Not working
> 
> I analysis my aac file and find out:
> stream time_base: 1/28224000
>    0:STM_IDX:0, isKey:1, dts:      0, pts:      0, duration:1310720, pos:      0, size:371
>    1:STM_IDX:0, isKey:1, dts:1310720, pts:1310720, duration:1310720, pos:    371, size:372
>    2:STM_IDX:0, isKey:1, dts:2621440, pts:2621440, duration:1310720, pos:    743, size:371
>    3:STM_IDX:0, isKey:1, dts:3932160, pts:3932160, duration:1310720, pos:   1114, size:372
> ....
> 
> The pts, dts, duration is so big and they are scary. Also the audio play too fast.
> Thanks !
> 
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This may help:

28224000 = 44100*640
As long as your time base can handle the sample rate you don’t need to have the exact time base with the sample rate. So it would be 640 ticks per sample in your case. But if you really must change the time base then i believe you have to rescale the timestamps of AVPackets using av_packet_rescale_ts

And even after doing that you may get a timescale value of 1/2*sampleRate in your stream.