[LAU] screencast using jack

[Patrick Shirkey]

On Tue, March 19, 2013 6:10 pm, Federico Bruni wrote:
> Il 19/03/2013 02:25, Len Ovens ha scritto:
>>> I have another issue with the tutorial above.
>>> >It says:
>>> >"Now you have two separate files, an .mkv and a .wav file and because
>>> >jack_capture was started right after ffmpeg audio should be no more
>>> out
>>> >of sync then just a few millisecs."
>>> >
>>> >Actually my files are out of sync because they have different
>>> durations.
>>> >Video is 5:31 and audio is 9:21.
>> My first guess is a frame rate issue... like a half frame rate that is
>> also mistranslated from 25hz to 29.*dropframe (or vise versa). It really
>> doesn't matter at this point, check two things. Listen to the wave, does
>> it sound right"? Watch the video stream, does it look really fast? Do
>> they
>> play back at the listed times?
>>
>> Are you using spdif for audio in? If so, where is it getting sync from?
>>
>> These are all shots in the dark. The first thing is to play them back
>> and
>> see if there is an issue with audio or video or both.
>
> Your guess is probably right.
> The audio is ok, while the video is a bit too fast.
>
> Yes, they play back at the listed times.
> Here's what ffmpeg say:
>
> Input #0, matroska,webm, from 'screencast_video_20130318-23h53.mkv':
>    Metadata:
>      ENCODER         : Lavf54.29.104
>    Duration: 00:05:31.00, start: 0.000000, bitrate: 426 kb/s
>      Stream #0:0: Video: h264 (High 4:4:4 Predictive), yuv444p,
> 1280x800, SAR 1:1 DAR 8:5, 30 fps, 30 tbr, 1k tbn, 60 tbc (default)
>
> Input #0, wav, from 'screencast_audio_20130318-23h53.wav':
>    Duration: 00:09:21.79, bitrate: 2304 kb/s
>      Stream #0:0: Audio: pcm_s24le ([1][0][0][0] / 0x0001), 48000 Hz,
> stereo, s32, 2304 kb/s
>
> But I don't understand... I've recorded at 30 fps and I'm watching at 30
> fps. Why it's playing faster than the recording?
>

It possible that your machine was dropping frames while recording. You can
slow down playback 'stretch" the video to the timelength you require.

http://ffmpeg.org/trac/ffmpeg/wiki/How%20to%20speed%20up%20/%20slow%20down%20a%20video




--
Patrick Shirkey
Boost Hardware Ltd