Keyframes and MPEG-2 editing

[ffooky]

I routinely record, edit and archive programmes recorded with EyeTV (DVB-T). The editor in EyeTV itself is fine for rougher stuff but I then export to MPG and do the finer cuts with MPEG Streamclip.

This is fine in most cases but some UK channels have a very annoying way of blending the last part of a show and their channel ID before commercial breaks (Five in particular) and this seems to be more problematic with programs transmitted in 4:3 and ads in 16:9. I always cut on keyframes but occasionally this still leaves a brief but infuriating flash of unwanted content. Is there any tool, OS X, Windows or Linux that will allow me remove this without necessitating any re-encoding or anything else major ?

On another point, the MPEG-TS inside each EyeTV recording is always much larger than the exported MPG and MediaInfo reports a higher bitrate. Is this merely a consequence of it being a transport stream and the extraneous info about other channels on the same frequency, or is the export genuinely lossy in terms of quality ?

[jagabo]

Womble's MPEG editor is smart -- it only reencodes GOPs that have changed, cut, in your case.

MPEG TS streams are 5 or 10 percent bigger than PS streams. If you're seeing a difference bigger than that you're reencoding with a different bitrate.

file size = bitrate * running time

(plus a little overhead for container)

[ffooky]

Thanks jagabo. I should have specified freeware but if the free trial cuts the mustard I'll consider springing for it.

I'll check the exact ratio between MPEG-TS and exported PS size with my next recording. EyeTV defines the export as not re-encoded and the process seems too fast but I'll check it out.

[Frobozz]

It isn't free and there is no free trial but Capty MPEG Edit EX is specifically designed to do frame-accurate editing of MPEG 2 files. It is available at pixela-1.com.

The EyeTV recordings are also in an EyeTV wrapper so it can be described, played and edited within EyeTV so that is another reason the file is larger than the exported MPEG 2 file.

[ffooky]

Frobozz, I've always assumed it was the .eyetvp, .eyetvi, .eyetvr and .tiff files within the .eyetv package that performed those functions. I currently don't have any recordings with a single audio track (preferably no subs either) to make a valid comparison.

Unfortunately I don't have £45 to spare at the mo...a secure free trial seems more likely to lead to a purchase than relying on people buying on the off chance but I suppose it must be working for them. Does it also only re-encode changed GOPs ?

[ffooky]

Well, after most of a day mucking around with MPEG Streamclip, MediaInfo, PVAStrumento (which runs very nicely under Wine on OS X) and a host of others...demuxing, transcoding etc. I've determined that EyeTV's export to MPG function does not involve any re-encoding.

When examining the .mpg file contained within an .eyetv bundle, most applications will only recognise the video and audio streams but anything that uses ffmpeg also spots the subtitles, EPG info and other sundry crap, some of which is pretty sizeable.

Demuxing a raw MPG of 1.07GB with ffmpegX produced:

000000000f398460.mpg-8294-1.unk 236.4MB
000000000f398460.mpg-8294-2.unk 45.7MB
000000000f398460.mpg-8294-3.unk 1.9MB
000000000f398460.mpg-8294-4.unk 1.2MB
000000000f398460.mpg-8294-5.unk 372KB
000000000f398460.mpg-8294-6.mp3 16.2MB (64kbps MP2 audio)
000000000f398460.mpg-8294-7.mp3 48.7MB (192kbps MP2 audio)
000000000f398460.mpg-8294-8.m2v 592.5MB (video track)

totalling 943MB

An MPG exported by EyeTV weighs in at 649.7 which is clearly the video + 192kbps audio. As to what the two large .unks are, I have no idea.

[Frobozz]

Frobozz, I've always assumed it was the .eyetvp, .eyetvi, .eyetvr and .tiff files within the .eyetv package that performed those functions. I currently don't have any recordings with a single audio track (preferably no subs either) to make a valid comparison.

I see your point. This may be a good question in the ElGato forum. I do know the exported MPEG file has no re-encoding so there is no loss of quality due to that export. I don't know why the exported file size is smaller.

Unfortunately I don't have £45 to spare at the mo...a secure free trial seems more likely to lead to a purchase than relying on people buying on the off chance but I suppose it must be working for them. Does it also only re-encode changed GOPs ?

I've used Capty MPEG Edit EX a few times. Mostly I used it when wanting to join MPEG files or when wanting to change MPEG audio to AC3. The frame-accurate editing is very clever in that it creates new GOPs around the edit by converting those frames to DV and encoding them back to MPEG 2 (at least that's how I think it does it). The result and speed are impressive. It is necessary to export from that application as elementary streams because its muxed MPEG export seems to only work with CaptyDVD.

Also, it might not accept your EyeTV exports. Here is info about limitations in MPEG Edit EX:
-Does not support MPEG-1 format files.
-Does not support VOB format files.
-Cannot load files of less than 0.5 seconds or more than 12 hours.
-Cannot load files with the timetable reset in midstream.
-Maximum length of files created is 12 hours and mimum length is 0.5 seconds. Note that for DV stream amd QuickTime movie, maximum length of files is 2 hours.
-Handles PCM, MPEG-1 Audio Layer-2, and Dolby Digital Audio formats.
-Handles 48KHz of audio sampling rate. Converts audio sampling rate of files other than 48KHz to 48KHz.
-MPEG-2 with audio sample size other than 16-bit is not supported.
-Handles video bitrate of 2Mbps to 9.8Mbps. Note that when audio format is PCM, maximum bitrate is 8Mbps.
-If video bitrate exceeds 8Mbps, you cannot select PCM as audio format.
-Does not support files with multiple audio streams.
-Handles up to 18 frames in a GOP for NTSC and 15 frames in a GOP for PAL.
-Handles system bitrate up to 10.08Mbps. Even if system bitrate is lower than 10.08Mbps, video bitrate higher than 9.8Mbps cannot be handled.
-Files can be combined in File Combination Mode if they are MPEG-2 format files and their video size, frame rate, aspect ratio, format of interlace and field order, audio sampling rate, and the number of audio channels are identical.
-Handles MPEG-2 format files as follows:
NTSC : 704 x 480, 720 x 480, 352 x 480, 352 x 240
PAL : 704 x 576, 720 x 576, 352 x 576, 352 x 288
-System bitrate is the total bitrate size comprising audio bitrate of MPEG-2 format files and video. Video bitrate varies according to audio bitrate.

(e.g.) When the system bitrate of MPEG-2 format file is 8Mbps, the result is as follows:
When the audio bitrate is 224Kbps, video bitrate will be approximately 7.2Mbps.
When the audio bitrate is 384Kbps, video bitrate will be approximately 6.9Mbps.

[PuzZLeR]

...some UK channels have a very annoying way of blending the last part of a show and their channel ID before commercial breaks (Five in particular) and this seems to be more problematic with programs transmitted in 4:3 and ads in 16:9. I always cut on keyframes but occasionally this still leaves a brief but infuriating flash of unwanted content. Is there any tool, OS X, Windows or Linux that will allow me remove this without necessitating any re-encoding or anything else major ?

The best tool to handle this is with Womble and a little craftiness.

What you do is cut the unwanted content down to a few frames on each side of where the series of ads begin and end. Then fade out the wanted content before the ads, and fade in the wanted content after the ads. It may even improve the program somewhat by artificially installing a millisecond break instead of a harsh transition this way.

As for re-encoding, only those few frames it fades will be re-encoded by Womble, otherwise completely lossless.

[ffooky]

@Frobozz - Thanks a lot for that info. It does indeed look as though I'd be out of luck with Capty MPEG Edit EX as PVAStrumento reported a few GOPs that were more than 15 frames. Given that list of requirements I'd be very reluctant to buy without trying.

@PuzZLeR - Womble's looking like a winner but I can't test it out at the moment as my Windows partition is temporarily out of action and I'm having no luck running it under Wine. Thanks.