videorate for encoded video

[Farkas Levente]

hi,
we'd like to make snapshots of an input encoded video stream.
does anybody have any tip how can we do this?
unfortunately videorate can only accept raw streams.
so suppose we've got a h264 input source and like to save the stream and
every 5 minutes a jpeg image, then this pipeline almost good:
---------------------------
gst-launch -e rtspsrc
location="rtsp://a-h264-url" ! rtph264depay access-unit=true ! h264parse
! tee name="t" ! queue ! matroskamux ! filesink location="test.mkv"  t.
! queue ! ffdec_h264 ! videorate !
video/x-raw-yuv,framerate=1/300 !
ffmpegcolorspace ! jpegenc ! multifilesink location="frame%05d.jpg"
---------------------------
but in this case we've to decode _all_ frames. and we'd like to save cpu
and only decode the required frames.
does anybody has any tips?
thanks in advance.
regards.

--
  Levente                               "Si vis pacem para bellum!"

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[Alexandru Csete]

On Wed, Sep 8, 2010 at 10:22 AM, Farkas Levente <[hidden email]> wrote:

> hi,
> we'd like to make snapshots of an input encoded video stream.
> does anybody have any tip how can we do this?
> unfortunately videorate can only accept raw streams.
> so suppose we've got a h264 input source and like to save the stream and
> every 5 minutes a jpeg image, then this pipeline almost good:
> ---------------------------
> gst-launch -e rtspsrc
> location="rtsp://a-h264-url" ! rtph264depay access-unit=true ! h264parse
> ! tee name="t" ! queue ! matroskamux ! filesink location="test.mkv"  t.
> ! queue ! ffdec_h264 ! videorate !
> video/x-raw-yuv,framerate=1/300 !
> ffmpegcolorspace ! jpegenc ! multifilesink location="frame%05d.jpg"
> ---------------------------
> but in this case we've to decode _all_ frames. and we'd like to save cpu
> and only decode the required frames.
> does anybody has any tips?

Hi Levente,

I don't think you can do that because h264 (and most other video
codecs) rely heavily on inter frame compression. I guess one could do
what you ask by only decoding the key frames, but that would probably
require writing your own decoder.

Alex

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[Farkas Levente]

On 09/08/2010 11:13 AM, Alexandru Csete wrote:

> On Wed, Sep 8, 2010 at 10:22 AM, Farkas Levente <[hidden email]> wrote:
>> hi,
>> we'd like to make snapshots of an input encoded video stream.
>> does anybody have any tip how can we do this?
>> unfortunately videorate can only accept raw streams.
>> so suppose we've got a h264 input source and like to save the stream and
>> every 5 minutes a jpeg image, then this pipeline almost good:
>> ---------------------------
>> gst-launch -e rtspsrc
>> location="rtsp://a-h264-url" ! rtph264depay access-unit=true ! h264parse
>> ! tee name="t" ! queue ! matroskamux ! filesink location="test.mkv"  t.
>> ! queue ! ffdec_h264 ! videorate !
>> video/x-raw-yuv,framerate=1/300 !
>> ffmpegcolorspace ! jpegenc ! multifilesink location="frame%05d.jpg"
>> ---------------------------
>> but in this case we've to decode _all_ frames. and we'd like to save cpu
>> and only decode the required frames.
>> does anybody has any tips?
>
> Hi Levente,
>
> I don't think you can do that because h264 (and most other video
> codecs) rely heavily on inter frame compression. I guess one could do
> what you ask by only decoding the key frames, but that would probably
> require writing your own decoder.

or simple decode only the required i frame and a few p frames instead of
all i and p frames....
that's what i looking for...

--
  Levente                               "Si vis pacem para bellum!"

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