<div dir="ltr">Well that did the trick! I can't thank you enough James and also second your comment that this should be updated in the transcoding.c example.<div>Is there anything we can do about this?</div><div><br></div><div>As for the GLOBAL_HEADER if I am not mistaken it is done indeed as you suggest, maybe this has been updated, here is the relevant code:</div><div><br></div><div> if (ofmt_ctx->oformat->flags & AVFMT_GLOBALHEADER)<br> enc_ctx->flags |= AV_CODEC_FLAG_GLOBAL_HEADER;<br> <br> /* Third parameter can be used to pass settings to encoder */<br> ret = avcodec_open2(enc_ctx, encoder, NULL);<br></div><div><br></div><div>Thanks again!</div></div><br><div class="gmail_quote"><div dir="ltr" class="gmail_attr">On Tue, Nov 5, 2019 at 2:03 PM James Crisafulli <<a href="mailto:james2048@gmail.com">james2048@gmail.com</a>> wrote:<br></div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex"><div dir="ltr"><div dir="ltr"><div>Hi,</div><div><br></div><div>I used to have the same issue with my application, which I based on transcoding.c (not transcoding but anyways, writing H264 to MP4 file).</div><div>You need to set the AVPacket duration field, for some reason it shows this issue if you let it automatically set it (set to -1).</div><div>I had to do this both using libx264 and mpeg4 encoders.</div><div><br></div><div>Example in my code from the muxing section:</div><div><br></div><div>av_packet_rescale_ts(&packet, codecCtx->time_base, stream->time_base);<br> packet.stream_index = 0;</div><div>// probably best to write this as av_rescale_* functions, but this is old code</div><div>// for example, if 25 FPS, and time_base is 12800, then packet.duration = 12800 / 25 = 512<br> packet.duration = stream->time_base.den / stream->time_base.num / stream->avg_frame_rate.num * stream->avg_frame_rate.den;<br>// now you can mux<br> ret = av_interleaved_write_frame(formatCtx, &packet);<br></div><div><br></div><div>I am not sure why this is needed, I found this in another codebase with a similar comment, and it fixed my issue.</div><div><br></div><div>Might as well mention that in transcoding.c, it also doesn't set the GLOBAL_HEADER flag at the right time, and as such you get a malformed file if writing MP4 format. I noticed it wouldn't open in Adobe Premiere, and Windows 10 Films & TV player, and ffprobe had warnings about it as well but did manage to read it.</div><div><br></div><div>// TOO LATE! has to be done before avcodec open!! In transcoding.c, it does this after the call and as such the flags are ignored.<br></div><div>if (formatCtx->oformat->flags & AVFMT_GLOBALHEADER)<br> {<br> codecCtx->flags |= AV_CODEC_FLAG_GLOBAL_HEADER;<br> }<br></div><div><br></div><div>To fix that, I have hard coded the flag early when I know I am writing MP4, before avcodec_open():</div><div><br></div><div>codecCtx->flags |= AV_CODEC_FLAG_GLOBAL_HEADER;<br> AVDictionary *encoderOpts = nullptr;<br> ret = avcodec_open2(codecCtx, codecCtx->codec, &encoderOpts);<br></div><div><br></div><div>And now everything works well for me. Hopefully it fixed the issues for you as well.</div><div>Would be nice to see transcoding.c updated to fix these small issues as it is used as a base by so many people looking into libav* development.</div><div><br></div><div>- James </div></div></div><br><div class="gmail_quote"><div dir="ltr" class="gmail_attr">On Tue, 5 Nov 2019 at 11:07, Vassilis <<a href="mailto:bpantazhs@gmail.com" target="_blank">bpantazhs@gmail.com</a>> wrote:<br></div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex"><div dir="ltr">This can not be reproduced with the ffmpeg cli, conversion works fine there.<div>However it can be reproduced with transcoding.c for all input files.</div><div>Additionally to what I mentioned, 29.96 fps test files result in 29.98 and 30 to 30.11.</div><div>Another 24 fps file resulted in 24.03. The changes seem to be related with </div><div>the duration of the file: the longer the file the shorter the marginal fps difference. </div><div>The output frame rate can be determined with both fffmpeg -i as well as with</div><div>QuickTime 7 and VLC. Like I mentioned, I have spent some time with investigating this</div><div>and it looks like an issue with the correct conversion of the last frame; I was able</div><div>to get different framerate values when tampering with the pts of the last frame</div><div>but this looked like a nasty hack that I shouldn't be doing, plus it fails</div><div>again when re-encoding the file. Here is the info from an input/output test file</div><div>that has the frame rate changed from 24 fps to 24.03:</div><div><br></div><div> Duration: 00:00:36.08, start: 0.000000, bitrate: 178309 kb/s<br> Stream #0:0(eng): Video: dnxhd (DNXHD) (AVdn / 0x6E645641), yuv422p10le(tv, bt709/unknown/unknown), 1920x1080, 176160 kb/s, SAR 1:1 DAR 16:9, 24 fps, 24 tbr, 23976 tbn, 23976 tbc (default)</div><div><br></div><div> Duration: 00:00:36.10, start: 0.000000, bitrate: 116072 kb/s<br> Stream #0:0: Video: dnxhd (DNXHD) (AVdn / 0x6E645641), yuv422p(tv, bt709/unknown/unknown), 1920x1080, 116526 kb/s, SAR 1:1 DAR 16:9, 24.03 fps, 24 tbr, 12288 tbn, 12288 tbc (default)<br></div><div><br></div><div>You'll notice that there is a slight change in the duration as well, but this happens with the ffmpeg conversion with the cli as well.</div><div><br></div><div>Let me know if you need more information and thanks for the help!</div><div><br></div></div><br><div class="gmail_quote"><div dir="ltr" class="gmail_attr">On Tue, Nov 5, 2019 at 3:42 AM Carl Eugen Hoyos <<a href="mailto:ceffmpeg@gmail.com" target="_blank">ceffmpeg@gmail.com</a>> wrote:<br></div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex">Am Di., 5. Nov. 2019 um 00:16 Uhr schrieb Vassilis <<a href="mailto:bpantazhs@gmail.com" target="_blank">bpantazhs@gmail.com</a>>:<br>
> I am trying simply to perform a transcoding process using the transcoding.c example from doc/examples. However I am seeing a very strange result (even when the example is not modified at all, ie not even changing codecs); the transcoded file has a marginally different frame rate than the original file. For example for a frame rate of 24 fps I get 24.14 fps. I also implemented this with the newer av_send/receive packet/frame functions to no avail. I would be most grateful for any insights, I've spent quite some time trying to troubleshoot this.<br>
<br>
Can you reproduce the issue with the ffmpeg cli or only with transcoding.c?<br>
<br>
Why do you think that the output frame rate is 24.14? What does ffmpeg<br>
-i show for your input file?<br>
<br>
Carl Eugen<br>
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