Hello.
I found one better method to fix this issue. Firstly, i think the problem
caused by incorrectly setting enc_ctx->time_base, so i refer to the
implementation in avcodec_open2()
361 #if FF_API_AVCTX_TIMEBASE
362 if (avctx->framerate.num > 0 && avctx->framerate.den > 0)
363 avctx->time_base = av_inv_q(av_mul_q(avctx->framerate,
(AVRational){avctx->ticks_per_frame, 1}));
364 #endif
this is new version code and i submit it in new mail, it can be reviewed in
https://patchwork.ffmpeg.org/project/ffmpeg/patch/tencent_7adfe69819d49d96fa8bc2c9e688ccec2...@qq.com/
- enc_ctx->time_base = av_inv_q(dec_ctx->framerate);
+ enc_ctx->time_base = av_inv_q(av_mul_q(dec_ctx->framerate,
(AVRational){dec_ctx->ticks_per_frame, 1}));
- enc_ctx->time_base = (AVRational){1, enc_ctx->sample_rate};
+ enc_ctx->time_base = (AVRational){1, dec_ctx->sample_rate};
but there is new issue in andriy/configure_x86 check:
error: Failed to merge in the changes.
i think it's maybe the mistake of branch? this patch is for release/5.1
branch rather than master branch.
Could any one give me some advice please so that i can fix it?
On Wed, Feb 5, 2025 at 11:25 AM Jack Lau <jacklau122...@gmail.com> wrote:
> To be clear, i want to give an example, i use a 10s duration, 30fps video.
> The ifmt_ctx->streams[stream_index]->time_base is same as
> ofmt_ctx->streams[stream_index]->time_base after initializing.
> The stream->dec_ctx->time_base is default 0,60 but
> stream->enc_ctx->time_base is set to av_inv_q(dec_ctx->framerate) so it's
> 0,30
>
> 174 /* video time_base can be set to whatever is handy and
> supported by encoder */
> 175 enc_ctx->time_base = av_inv_q(dec_ctx->framerate);
>
> so the twice rescale is this:
> input pkt in_tb: 15360 out_tb: 60
> output pkt in_tb: 30 out_tb: 15360
>
> so i get one 20s duration and 15fps video(audio duration is normal because
> the input's audio sample ratio is 44100)
>
> So i think the problem is that the enc_ctx->time_base shouldn't set to
> av_inv_q(dec_ctx->framerate)
>
> On Wed, Feb 5, 2025 at 10:29 AM Jack Lau <jacklau122...@gmail.com> wrote:
>
>>
>> AVCodecContext.time_base is not used for decoding.
>>
>>
>>
>> Thank you for your reply. I understand that time_base is not used during
>> decoding, but the transcoding code calls av_packet_rescale_ts twice,
>> once before decoding and once after encoding, as shown below:
>>
>> 540 if (filter_ctx[stream_index].filter_graph) {
>> 541 StreamContext *stream = &stream_ctx[stream_index];
>> 542
>> 543 av_log(NULL, AV_LOG_DEBUG, "Going to reencode&filter the
>> frame\n");
>> 544
>> 545 av_packet_rescale_ts(packet,
>>
>>
>> 546
>> ifmt_ctx->streams[stream_index]->time_base,
>> 547 stream->dec_ctx->time_base);
>> 548 ret = avcodec_send_packet(stream->dec_ctx, packet);
>>
>> 448 /* prepare packet for muxing */
>>
>>
>> 449 enc_pkt->stream_index = stream_index;
>> 450 av_packet_rescale_ts(enc_pkt,
>> 451 stream->enc_ctx->time_base,
>> 452
>> ofmt_ctx->streams[stream_index]->time_base);
>> 453
>> 454 av_log(NULL, AV_LOG_DEBUG, "Muxing frame\n");
>> 455 /* mux encoded frame */
>> 456 ret = av_interleaved_write_frame(ofmt_ctx, enc_pkt);
>>
>> If dec_ctx->time_base and enc_ctx->time_base are not consistent, it can
>> lead to incorrect packet duration, which in turn causes issues with the
>> output file's duration.
>>
>
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