[PD] Re: [GEM-dev] Codecs in Gem (again!) & ffmpeg

[B. Bogart]

Correction:

I just created a TOC from a mpeg2enc -f 1 file and I CAN seek backwards!

I was confused because a -f 0 mpeg (mpeg1) did not allow this, and
"file" reports my -f 1 (mpeg2) stream as a v1 stream... blech.

Anyhow I need to tweak the quality a bit and we're in business.

For the archives this is the command I used to create the mpeg2 from
frames using mjpegtools:

jpeg2yuv -f 25 -I p -v 0 -j ./test/link/%d.jpg | mpeg2enc -o test3.mpg
-g 1 -G 1 -f 1 && mpeg3toc test3.mpg test3.toc

which looks pretty ugly for the record, even being 600MB (small)

Thanks all.

B>

B. Bogart wrote:
> Hi all,
>
> Thanks for the wealth of info.
>
> I made a couple mpegs and TOCs and it works fine. I decided to create
> GOPs of only a single frame to force the lack of interframe compression.
>
> So it *almost* works in Gem, almost eh...
>
> Well I can seek only forwards, not backwards.
>
> Lets call the current frame Fc and the previous frame Fp:
>
> if Fp < Fc
>   seeking works fine
> if Fp > Fc
>   the mpeg immediatly jumps to the first frame and sticks on the first
>   frame for as long as this condition is true.
>
> Maybe I need a 2 frame GOP to get bidirectionality?
>
> I've been unable to seek any mpeg at all without using the mpeg3toc
> thing, Including my single frame GOP, they just scrub forward as you
> twiddle the frame number.
>
> We'll I'm close anyhow. off to look at lvs-studio...
>
> Thanks again,
>
> B.
>
>
>
> chris clepper wrote:
>
>> On Aug 30, 2005, at 10:05 PM, B. Bogart wrote:
>>
>>> Thanks for the suggestions.
>>>
>>> I'm not sure about using a mpeg for the following reasons:
>>>
>>> #1. was does the interframe compression thing work, in other words how
>>> does it compare when seeking to a quicktime with photo-jpg codec?
>>
>>
>>
>> You want to avoid interframe compression at all costs.  In order to
>> grab a random frame in an interframe codec the nearest previous
>> keyframe must be found and all interframes between it and the  requested
>> frame are decoded.  You could get lucky and hit a keyframe  or be very
>> unlucky and hit the frame right before one.
>>
>> Interframe  compression techniques are used almost exclusively for
>> final content distribution (web, DVD, ATSC).  Acquisition and
>> production codec never use this with the exception of HDV (which is
>> MPEG2).
>>
>>> Aside: What id the different between mjpeg and photojpeg as a video
>>> codec?
>>
>>
>>
>> mjpeg is motion-jpeg which is for interlaced two field video.  Each
>> field (50 or 60 per second) is a compressed with jpeg techniques.
>>
>>> ffmpeg reports my sequence of jpegs as "mjpeg"...
>>
>>
>>
>> It is mistaken if your sequence is single progressive frames, which  it
>> almost certainly is.
>>
>> cgc
>>
>> _______________________________________________
>> PD-list at iem.at mailing list
>> UNSUBSCRIBE and account-management ->
>> http://lists.puredata.info/listinfo/pd-list
>>
>
> ------------------------------------------------------------------------
>
> _______________________________________________
> PD-list at iem.at mailing list
> UNSUBSCRIBE and account-management -> http://lists.puredata.info/listinfo/pd-list

-------------- next part --------------
A non-text attachment was scrubbed...
Name: signature.asc
Type: application/pgp-signature
Size: 256 bytes
Desc: OpenPGP digital signature
URL: <http://lists.puredata.info/pipermail/pd-list/attachments/20050831/0f39dac5/attachment.pgp>