avconv complains "non monotonically increasing dts to muxer in stream" when piping from libx264 on 14.04

Question

I have a piece of code that takes a stream of images and writes them to a file using x264 to encode and avconv. The relevant bits are as follows

// Setup encoder
sprintf(cmd, "avconv -i pipe: -vcodec copy %s", filename);
fp = popen(cmd, "w");
x264_param_default_preset(&params, "ultrafast", "stillimage,zerolatency");
params.i_fps_num = fps;
params.i_fps_den = 1;
x264_picture_alloc(&in, X264_CSP_I420, width, height);
params.i_csp = X264_CSP_I420;
in.img.i_csp = X264_CSP_I420;
x.params.b_vfr_input = 0;
in.i_pts = -1;
out.i_pts = -1;
params.i_width = width;
params.i_height = height;
encoder = x264_encoder_open(&params);

in.img.i_plane = 1;
in.img.i_stride[0] = width;
ret = x264_encoder_headers(encoder, &nals, &nheader);
header_size = nals[0].i_payload + nals[1].i_payload + nals[2].i_payload;
fwrite(nals[0].p_payload, header_size, 1, fp);

...
// Loop body
++in.i_pts;
frame_size = x264_encoder_encode(encoder, &nals, &num_nals, &in, &out);
fwrite(nals[0].p_payload, frame_size, 1, fp);

I've left out error checking for clarity, but no error is ever returned. Indeed, until I upgraded my system to 14.04, this code worked perfectly (and continues to work perfectly for colleagues who've yet to upgrade).

Only now running Ubuntu 14.04, I get this output from avconv

[h264 @ 0x98dec0] Estimating duration from bitrate, this may be inaccurate
Input #0, h264, from 'pipe:'
  Duration: N/A, bitrate: N/A
    Stream #0.0: Video: h264 (Constrained Baseline), yuv420p, 640x480, 25 fps, 25 tbr, 25 tbn, 60 tbc
Output #0, mp4, to '../reel/test.mp4':
  Metadata:
    encoder         : Lavf54.20.3
    Stream #0.0: Video: libx264, yuv420p, 640x480, q=2-31, 25 tbn, 25 tbc
Stream mapping:
  Stream #0:0 -> #0:0 (copy)
[mp4 @ 0x1347800] Application provided invalid, non monotonically increasing dts to muxer in stream 0: 2 >= 2
av_interleaved_write_frame(): Invalid argument

Despite the error, out.i_dts does monotonically increase over the whole duration of the video (it's always equal to in.i_pts).

My general assumption is that newer versions of avconv are more strict with the parameters of the input stream, so while my choice of parameters may have worked before, they do not work now.

Another curiousity, which might be related, is avconv detecting that the stream is 25 FPS, even though x264 is configured with an input FPS of 30.

Edit: Some further information, the same dts error (2>=2) happens regardless of the initial pts (with the output dts matching as expected).

Rachal

I found this question in DDG after FFMPEG gave this error. The problem was an invalid subtitle file. One of the subtitle time stamps occurred before a previous one. I just edited the VTT file in a text editor and deleted it. The invalid subtitle happened to be at the beginning of the file. I believe the faulty time stamp is given by x >= x where x is the milliseconds. – Ipoh

Answer 1

In a moment of "I don't know why this should fix it, but does", changing -vcodec copy to -vcodec libx264 (even though the source codec was already libx264) fixed the dts error.

Rachal

Yes, this works. But it may be that ffmpeg now does not just dump the stream, but it also re-encodes it. – Thrifty

With ffmpeg, my workaround to avoid this error (which I've encountered only with mp2 files) is to drop the start of the file (i.e. remove the first few milliseconds) by adding the following to the ffmpeg command line, so that the file downloads without the first 15 thousandth of a second (but it might be necessary to experiment with the value, in individual cases, as I doubt all files will be identical, so the first step would be to increase the value from 0.015 to some larger figure): -ss 0.015 – Lynnelynnea