Finding I-Frames in MPEG-2 PS or TS

[ruby33]

Hi guys,
I am trying to find out a way to detect I-Frames in a Mpeg2-PS or TS stream.
I tried it with Mpeg2-PS, as in started looking for the occurrence of the byte sequence "00 00 01 00" for all MPEG-2 PS Packs having a PTS or PTS and DTS with stream type E0 (Video Stream). With this, atleast the I-Frame,P-Frame and B-Frame count matched with that of VirtualDubMod 1.5... Please let me know if this is a correct approach or not.

Thanks,
Ruby

[Guest]

It's too stringent as it is not required that all frames carry PTS/DTS (they can be interpolated), and there are other video stream ids than E0.

[ruby33]

Hi neuron2 thanks soo much for the reply.
Then how is it that i can figure out which Streams contains frames? Is there some documents on the same.
So far the samples which i have contains only EO video frames. Verifying the same with wireshark. If you can point me to the right direction it will be of great help
Thanks,
Ruby

[ruby33]

Hi Neuron , there is a small question which i want to ask.
In wireshark, they say the first Pack always contains the quantization matrix and my first I-Frame is always contained in that. Again i am a noob. If you could take sometime in explaining or point me to a document which does describe everything it will be of great help. Please

Ruby

[Guest]

Refer to the MPEG2 spec for details on stream IDs. You just need to check for the possible legal stream IDs. Almost always it is 0xe0 but I have seen other cases.

I don't know what wireshark is but what you've quoted is not necessarily true.

Just parse for 00 00 01 00 in your elementary video stream and for field pictures count half a frame and for frame pictures count a full frame. Don't make the job harder than it is.

[ruby33]

Thanks a lot neuron , i will complete this work and get back to you.. thanks again.

[kreet]

neuron2: wireshark is the new ethereal.

ruby33: I,P and B -frames are elements in MPEG compression, not the MPEG 2 Transport/Program Stream spec. you cant really rely on PTS/DTS field for information about frames. you need to move up a layer to the elementary stream itself. most streams mark frames clearly in their packets.

you should look at the mpeg2 compression specs or mpeg4 if you are inspecting a mpeg4 encoded video transmitted over mp2ts.

[ruby33]

Hi kreet,I have to learn MPEG-2 and will currently be in studying the same. my idea is to first learn about the PES structure as in able to differentiate between the I,B,P Frames . In order to do that i have started digging into Mpeg2 PS. After i am able to do that i will start working on Mpeg2-TS. With the Mpeg2-ts i have to handle the adaptation field also. I figured it will be easier this way. Ultimately i have to learn MPEG-2 Codec . Thanks for the help
-Ruby

[kreet]

m2ts is the 'Systems' portion of mpeg-2 and covers both PS and TS. they are very similar. I,B,P frames are not covered by this standard at all, you need the 'Video' section 2 (13818-2).

for more on Systems see http://en.wikipedia.org/wiki/MPEG_transport_stream and the standard itself: ISO 13818-1

for more on Video see http://en.wikipedia.org/wiki/Mpeg2, http://en.wikipedia.org/wiki/Video_compression and the standard ISO 13818-2

you should really read and understand the standards first before trying to implement things ;)

[eslave]

MPEG Video stream values are 0xE0 through 0xEF, but scanning for Picture codes alone would certainly be easier.

The last time I dared to tinker with this stuff I made extensive use of these two pages:
http://dvd.sourceforge.net/dvdinfo/mpeghdrs.html
http://dvd.sourceforge.net/dvdinfo/pes-hdr.html
Though slightly lacking in some details I found it much easier to digest than the ISO docs. :)

Learn to use your programming language's bit-shift operations to place the LSB where it belongs, and then use the bit-wise AND operator to mask-off any remaining unwanted bits. Knowing how to merge bytes into words or doublewords and using 64-bit data-types for playing with 33-bit (how handy!) timestamps can also prove useful.

-eslave

[ruby33]

Hi Eslave and kreet,
Thanks a lot to both of you. kreet i couldn't get my hands on the Video Doc 13818-2 and eslave.. Yes i had to depend a lot on the webpage u made it was really helpful.
Now i will be doing research on how to Joining video clips without getting artifacts. When i just tried joining video clips from two different source , i ended up getting artifacts and the error i think was because of the mismatch of Presentation Time Stamps. Anyways thanks again.

Cheers,
Ruby

[Guest]

i couldn't get my hands on the Video Doc 13818-2 Did you try here:

http://neuron2.net/library/mpeg2/iso13818-2.pdf

[ruby33]

Thanks neuron