[FFmpeg-devel] Live encoding into mxf...

[Eng. Tweellt]

Hi Michael,

I did what you've suggested and found out how to encode directly from a
live source and it works indeed. I got some buffer alerts but the output
video was much better than mine, without artifacts.

When I'm encoding should I order the frames in some way?

Cheers

2015-02-27 10:05 GMT+00:00 Eng. Tweellt <tweellt at gmail.com>:

>
> 2015-02-26 23:46 GMT+00:00 Michael Niedermayer <michaelni at gmx.at>:
>
>> On Thu, Feb 26, 2015 at 05:26:36PM +0000, Eng. Tweellt wrote:
>> > Hello everyone,
>> >
>> > I'm trying to encode video and audio directly from a capture board, 1
>> video
>> > stream and 8 single channel audio streams into a MXF file encoding it in
>> > Mpeg-2.
>> >
>> > Everything is working fine except when I call av_write_trailer() at the
>> end
>> > (and before freeing CodecContext as stated in the documentation).
>> >
>> > After using av_write_trailer, I end up with the whole video looking like
>> > this http://i.imgur.com/M6HkcpR.jpg . It seems like the decoder is
>> > misplacing the b-frames in the wrong position, but  If i don't call this
>> > function I can play the media file, with the image as it should be, in
>> VLC
>> > but the timestamp is completely wrong.
>> > Looking at mediainfo I can see that my file doesn't  have the file
>> duration
>> > (which later made sense when I looked inside the code.)
>> >
>> > After a few hours with the file mxfenc.c  found  that if I comment the
>> next
>> > part inside the function mxf_write_footer(), the write trailer "kinda"
>> > works,
>> >
>> > (...)
>> > if (mxf->edit_unit_byte_count && s->oformat != &ff_mxf_opatom_muxer) {
>> //
>> > no need to repeat index
>> >         if ((err = mxf_write_partition(s, 0, 0, footer_partition_key,
>> 0)) <
>> > 0)
>> >             return err;
>> >     } /*else {
>> >         if ((err = mxf_write_partition(s, 0, 2, footer_partition_key,
>> 0)) <
>> > 0)
>> >             return err;
>> >         mxf_write_klv_fill(s);
>> >         mxf_write_index_table_segment(s);
>> >     }*/
>> > (...)
>> >
>> > The "kinda" works part, its because I can play the file correctly in VLC
>> > with the correct timestamps, and if I open it with Mediainfo everything
>> > looks good, but If I try to open it with Sorenson Squeeze (for
>> example), I
>> > get a warning saying  "Squeeze does not support playing this file".
>> > I carefully followed the documentation, samples, examples and I'm still
>> > stuck :S.
>> > I am using the ffmpeg 2.5.1 version and I also added a few changes that
>> I
>> > saw in the master, and nothing changed.
>> >
>> > Additional info:
>> >
>> > Target Output file format is a 1080i59.94, XDCam 30Mbit MXF op1a.
>> >
>> > Regarding the 8 audio streams the codec options have the one provided by
>> > avcodec_get_context_defaults3 plus this changes:
>> >
>> > audio_codec_context->channels=1;
>> > audio_codec_context->sample_rate = 48000;
>> > audio_codec_context->bit_rate = 768000;
>> > audio_codec_context->sample_fmt =AV_SAMPLE_FMT_S16;
>> > audio_codec_context->flags= CODEC_FLAG_GLOBAL_HEADER;
>> > audio_codec_context->time_base->num = 48000;
>> >
>> >
>> > Regarding video  I also do avcodec_get_context_defaults3 plus this:
>> >
>> > video_codec_context-> pix_fmt= AV_PIX_FMT_YUV422P;
>> > video_codec_context->height = 1080;
>> > video_codec_context->time_base->den = 30000;
>> > video_codec_context->time_base->num = 1001;
>> > video_codec_context->field_order= AVFieldOrder.AV_FIELD_TB;
>> > video_codec_context->width = 1920;
>> > video_codec_context->codec_id= AV_CODEC_ID_MPEG2VIDEO;
>> > video_codec_context->has_b_frames= 1;
>> > video_codec_context->max_b_frames = 2;
>> > video_codec_context->gop_size= 12;
>> > video_codec_context->global_quality= FF_QP2LAMBDA * 1;
>> > video_codec_context->rc_initial_buffer_occupancy= 10695476;
>> > video_codec_context->scenechange_threshold = 1000000000;
>> > video_codec_context->color_primaries= AVCOL_PRI_BT709;
>> > video_codec_context->color_trc= AVCOL_TRC_BT709;
>> > video_codec_context->qmin= 1;
>> > video_codec_context->flags |= CODEC_FLAG_GLOBAL_HEADER |
>> > CODEC_FLAG_INTERLACED_DCT | CODEC_FLAG_INTERLACED_ME;
>> > video_codec_context->bit_rate =   30000000;
>> > video_codec_context->rc_min_rate= 30000000;
>> > video_codec_context->rc_max_rate= 30000000;
>> > video_codec_context->rc_buffer_size= 10695476;
>> >
>> >
>> > I also had specified me_method and me_range, but nothing changed.
>> >
>> > Any idea what might be the problem?
>>
>> can the problem be reproduced with command line FFmpeg ?
>>
>> [...]
>> --
>> Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB
>>
>> While the State exists there can be no freedom; when there is freedom
>> there
>> will be no State. -- Vladimir Lenin
>>
>
>
> Hi Michael,
>
> I can't really tell. Encoding from another file seams to work fine but
> encoding from a live source it does not.
>
> Now there are some differences, for instance when getting frames from a
> live source I have to deal with PTS values, duration and so on.
>
> Is there a way to encode directly from a live source using command line?
>
> Cheers
>
>