Workflow for DVB recordings in 1080i

[McEric]

Hello,

I have a ton of .ts files in 1080i that I recorded from DVB-C, and I want to make really sure I don't mess up when I edit them for archiving. I could use some guidance regarding two topics that got me confused.

1.) I've read the article Editing MPEG capture (DVB or IVTV) in the Wiki. As I understand it, the article wasn't written for recordings in HD. Neither ProjectX nor MPEG-PS seem to be supporting video tracks in H.264. Are there similar steps needed when dealing with recordings in 1080i? How would I go about that?

2.) As I understand it, I should be able to produce a file in 1080p25 from a recording in 1080i50. That's what I'm trying to achieve, ultimately. However, after experimenting a bit, I got pretty confused by the results.

Before any editing is done, VLC shows the file as having 25 fps. File -> Information in Avidemux seems to count the fields, not the frames, so it shows 50 fps. When navigating around the timeline, the steps between individual frames are 40 ms, so there are indeed 25 frames per second. After re-encoding the video stream to h.264 with a smaller bitrate, VLC shows the video as containing 50 fps. When observing the file in Avidemux, there are still 25 frames per second (and File -> Information still shows 50 fps). That's the first part that I don't understand.

The second part is that the filters for deinterlacing also produce unexpected results. "Merge Fields" produces a video with the resolution of 1920x2160. Both VLC and Avidemux show the frame rate as 25 fps, but the steps between the frames are 80 ms, so the real frame rate is 12.5 fps. Using YADIF with the preset "Temporal & spatial check" produces a file with the correct resolution, but both VLC and Avidemux still show the video as containing 50 frames per second. In both cases, I was expecting to get a progressive file in 1920x1080 with 25 frames per second. It's clear that I have no idea what I'm doing, but what exactly am I missing?

Thank you for your time,
Eric

[eumagga0x2a]

I'd recommend to avoid reencoding at almost any cost. if you can't avoid reencoding, add the "Change fps" filter to Yadif (if you can't use hw accelerated deinterlacing) converting from 25(!) fps to 25 fps as a workaround.

There are more issues with 1080i h264 streams like mistedected keyframes.

[zakk]

Do not rely too much on FPS information given by softwares.

[AQUAR]

ADM has had this issue of confusing fields with frames with interlaced AVC video for a long time.
The work around (see eumagga0x2a reply above) has been to add the Change fps filter to the deinterlacing filter chain and set it up as "from 25 fps to 25 fps".
This sets the meta data correctly for other video information software to properly report the frame rate of the recoded video.

[McEric]

Thank you all for the suggestions!

I'll have to re-encode many of the videos to resize them for storage reasons. Actually, that's a major reason for deinterlacing them in the first step - I want to ensure that the full resolution is used as the input for the resize filter. Not sure if the resize filter would do that anyway. I think I won't re-encode the ones I want to keep in 1920x1080 or just a very small part, so I can cut between keyframes.

Using the Change FPS filter to correct the metadata is a good idea, thanks. This information clearly doesn't match the actual video in the cases where Avidemux writes it as 50 fps.

One more thing I noticed: Re-encoding without any filters changes the scan type displayed by MediaInfo to from MBAFF to progressive. Don't know what to make out of that.