Question Panasonic recording setup (HG)

[_Dragon_]

The camcorder im using has its setting on HG 1080 is that what it should be set on? Done a bit of reading and it seems these setting are to do with compression? So its Quality of the recording.

 

[Terfyn]

HG 1080 is the second to lowest quality. Either go for 1080/50p or PH 1080/50i.
Don't know the model number but at the back of your User Manual there is a section:-
Recording modes/approximate Recordable time
This will give you a rough idea of quality vs recording time. I use 1080/50p as standard.

 

[_Dragon_]

At the moment im using a Panasonic HCV770, recording in AVCHD so i can put it on a usb stick to play through the bluray player, Ill have to look through the manual if i can find it,Thanks.

 

[dosdan]

The camcorder im using has its setting on HG 1080 is that what it should be set on? Done a bit of reading and it seems these setting are to do with compression? So its Quality of the recording.

Here is a 2-part msg I posted on the Photography (and Video) forum at forums.whirlpool.net.au concerning what compromises would be required to reduce the media consumption rate to 4GB/hr. Since it discusses how various parameters affect the compression achieved, and it uses the formats available in a HC-V750, the same formats as in the HC-V770, I think it's worthwhile reading it all and trying to get to grips with the concepts....

Video data is enormous. When shooting Full HD, each frame (a picture typically taken 25 or 50 times a second) is 1920px wide & 1080px high. So there are 1920x1080 pixels in a frame = 2MP. A byte is 8 bits. Since the colour is 24 bits in depth, there are 3 bytes/pixel, so each frame requires 6MBytes. At 50p (50 frames/sec, no interlacing), 1 minute of uncompressed video requires 6MB * 50fps * 60secs = 18GB/min. So obviously, compression is required.

One way to reduce the data rate is to reduce the frame size. 1080p or 1080i ("p"= progressive i.e. non-interlaced, "i" = interlaced) is 1920x1080. 720p (I don't think 720i is ever offered) is 1280x720 = 921KB (using a "K" of 1,000, not 1,024). So shooting in 720p would more than halve the data rate compared to shooting at 1080p. This drop in framesize is good if the destination is the internet.

Another way is to reduce the frame rate. Shooting at say 720p25 (25 frames/sec, no interlacing) would halve the date rate compared to shooting at 720p50. But fast action will look smoother at 50p than at 25p. So the choice would depend on how static or active the subject is.

Then we have interleaving. This was introduced in the very early days of TV to reduce the transmission bandwidth. Instead of transmitting a new frame every 1/50th of a second, a half-frame aka 1 field is transmitted, consisting of every 2nd horiz. line. So Field1 contains Line1, Line3... while Field2 contains Line2, Line4 ... This greatly reduces the amount of data being sent every 1/50th of a second. Now if the scene contains a vertical edge moving horizontally, its position in Field 2 will be different from Field 1 because the later field was recorded 1/50s later. If we pause playback of interlaced video, the combining of Field1 and Field2 to make a complete frame means that we see "combing". There are ways around this, but they involve loss of vertical resolution and can make mistakes. You'll sometimes see this in TV news broadcasts. If the pros still have problems with interlaced content, what hope have us amateurs? I think that interlacing is like a pact with Satan: enticing, but problematic. In today's HQ video environment, interleaving is best avoided.

So correctly, 50p is 50 frames/sec, but 50i is really 50 fields/sec. You can just use "fps" for both.

Finally we come to compression. I won't go into the nitty-gritty because it's very complex. Most video recording is variable bit-rate, so more bits are used in a complex scene with movement than in a simple static scene. There is a maximum bitrate and a lower typical biterate. Since much of the background, or in the case of a static scene, all of the data may not change significantly between frames, it is possible to record a large keyframe aka I-frame and then follow it by number of smaller partial frames aka P-frames & B-frames that just indicate changes. This greatly reduces the avg. bitrate, but makes it more problematic when you go to edit it, since a new keyframe may only occur say every 15-18 frames in the relatively low-compression MPEG-2 format used on DVDs, or every 30-33 frames in the highly-compressed AVC formats.

Compression is occurring both spatially (within a single frame, similar to how JPEG reduces the size of a photographic image) and temporally (between frames). As we keep decreasing the bitrate through heavier and heavier compression, compression artefacts become visible, like blockiness in action scenes, and the loss of fine detail.

Part 2 follows...

 

[dosdan]

Now I'll demonstrate the actual effect of these format choices on filesize. I'll use the formats in my Panasonic HC-V750, but show you how you can get them for your Sony.

You'll need to get the free MediaInfo MediaInfo

When you install this small program, it brings up a preferences menu. The only thing you need to do here is to click the box "Explorer Extension" so you can later R.click on a media file in Windows Explorer and examine it in MediaInfo.

Record a 60s clip using each of the format choices in your camera. Then load the SD card in a reader and R.click on each file and choose MediaInfo.

Here's my results. Mine's an American model so it has 30/60 fps:

AVCHD – all Full HD (1920x1080)

Option  60s  Bitrate (max/typ)  1HR      BPF
        MB     Mbits/sec         GB    Bits/(Pixel*Frame)
60p    180     28/25            10.8    .190
PH     154     24/21.5          9.24    .325
HA     113     18/15.7          6.78    .236
HG      87.9   18/12.3          5.27    .184
HE      35.2   18/4.93          2.11    .070

PH, HA, HG, HE are all 60i


MP4

Option         60s      Bitrate (max/typ)  1HR       BPF
                MB         Mbits/sec        GB   Bits/(Pixel*Frame)
1080p60 50M    325         49.2/45         19.5     .362
1080p60 28M    183         26/25.2         10.9     .202
720p30          58.2       14/8.0           3.49    .289
iFrame (540p30) 65.0       26/8.95          3.9     .576

On the SD card, you'll find the AVCHD files in the the \PRIVATE\AVCHD\BDMV\STREAM directory, with .MTS file extensions e.g. 00006.MTS.

MP4 files are found in uniquely named session directories under \DCIM e.g. \DCIM\207YAPHH\S2070001.MP4

MP4 & AVCHD both use H.264 aka MPEG-4 Part 10 aka MPEG4-AVC video compression. There are differences in the audio compression formats used in these 2 container formats. (A media "container" format, like MP4 or AVCHD, is just a wrapper around a compressed video format file and a compressed audio format file. The use of a container ensures that both the video and audio portions aka streams of the recording say together during distribution, and that they remain in sync when played back.) AVCHD also supports ancillary data. For the same level of compression, an AVCHD version will be slightly bigger. The audio in both formats is 1%-2% of the final filesize.

The 1hr filesize is just the 60sec filesize * 60.

The Bits/(Pixel*Frame) value takes into account the framesize & frame rate, and shows how many bits in the data stream are being used to encode each pixel in a frame. In the 1st posting I mentioned that uncompressed data requires 24 bits/px to quantify each pixel's colour and brightness, so if I understand this correctly, 0.190 bits indicates that the video compression ratio is 24:0.190 = 126:1. So, 1080p60 takes up 0.18GB/min, instead of 21.6GB/min uncompressed. (This is approx. 120:1 instead of 126:1, but it includes the audio and container overhead too.)

You can see, when comparing AVCHD 60p and PH-level of compression, where the typical bitrates are not that dissimilar, but the BPF is higher for PH, how interlacing improves either the quality (less compression applied) at similar bitrates, or allows a similar quality at a lower bitrate. Of course, with 60i, there's effectively only 30 full frames redrawn per second.

In the MP4 list, you can see that interlacing is not offered at all with this format. 720p is 1280x720 and 540p is 960x540. Notice also that the BPF of the iFrame format is relatively high, indicating lower compression. This is because a simpler level of compression is used to suit playback in a mobile device with its lower CPU power.

You can see to get below 4GB/hr, on this camera you'd need either to record using 720p30 in-camera, or convert it later in a program like AVIDEMUX or HANDBRAKE.

Dan.

 

[Terfyn]

Well that really cleared it up. You can get the manual on line through the Panasonic web site. I have the 750 which was replaced by the 770.

 

[_Dragon_]

@dosdan thanks but thats a bit to much information for a beginner to take in.

Ive been reading up a bit if editing in 1080i this can be tough and slow on the pc is that right? And some media players cant handle it if playing on a pc, Is there any truth in this?

 

[dosdan]

Ive been reading up a bit if editing in 1080i this can be tough and slow on the pc is that right? And some media players cant handle it if playing on a pc, Is there any truth in this?

Modern PCs should be able to handle 1080i. Laptops may have a problem, depending on the model. If the real-time playback is jerky inside your video editor due to the amount of processing being performed on-the-fly, you may have the option to select smaller (Auto/Full/Half/Quarter) and less processed (Draft/Preview/Good/Best) previews. (These are the options I see in Sony Vegas.) Doing so doesn't affect the quality of the final rendered version, only how you'll see it when working on it.

As regards playing 1080i media in a PC, any free media player (MPC-BE, MPC-HC, VLC) will handle it.

Regarding the complexity of this topic: yes, a lot of new information, all at once, is intimidating. I suggest you play around with your camera and MediaInfo over the next few days. Reread those 2 msgs, go away, experiment with the different formats on your camera and use MediaInfo to examine the output, take a break, reread, experiment some more, see the visible problems of using low bitrates with a subject with fast motion... and you'll find that your understanding of the topic will soon coalesce. The pay-off for you will be that you'll have sufficient understanding of the trade-offs involved in video compression to be able to make your own informed choices, rather than just relying on what people recommend.

Dan.

 

[Terfyn]

You need a well spec'd PC to run any current editor. For example, if you go on the Corel web site for VideoStudio, you will find a "minimum" specification for your PC to run that editor. I always record in 1080/50p and, yes, occasionally the PC stutters with the edited preview BUT when the video is rendered into your chosen format the resulting output is perfect - so there is a slight trade off.

The pay-off for you will be that you'll have sufficient understanding of the trade-offs involved in video compression to be able to make your own informed choices, rather than just relying on what people recommend

We recommend what we find works with a certain camera. I have the 750 which, as I said before, is the slightly older version of the 770 i.e. it has the same basic spec. I record in the best quality the camera will give me and then render two files, one in MPEG-2 for a standard DVD and a second in AVC/H.264 which gives a AVCHD file suitable for replaying on my Blu-Ray player. To me it makes sense to record in the best quality possible.

 

[_Dragon_]

I suppose you really want to film in the best possible quality mode even if you dont need it to be at this precise moment as then its future proofed for when you might upgrade your equipment,As its always going to be easier to compress the video than you needing to improve the video. So i suppose the question is do you record in 1080i or 1080P.

Merry Xmas

Everyone.

 

[_Dragon_]

HG 1080 is the second to lowest quality. Either go for 1080/50p or PH 1080/50i.
Don't know the model number but at the back of your User Manual there is a section:-
Recording modes/approximate Recordable time
This will give you a rough idea of quality vs recording time. I use 1080/50p as standard.

Does setting it to mp4 make it any better or less than setting it to Avchd?

 

[dosdan]

Does setting it to mp4 make it any better or less than setting it to Avchd?

As mentioned in my 2 msgs, both these container formats are using h.264-compressed video streams. It's the video compression method, framesize, whether interleaving is used and the bitrate that determines the ultimate quality. If all these are similar, since the video compression method is the same for both formats, the picture quality will also be very similar. The two progressive choices below from the formats offered in the V750 will look pretty much the same:

Option                  60s   Bitrate (max/typ) 1HR       BPF
                        MB        Mbits/sec      GB  Bits/(Pixel*Frame)
ACVHD 60p              180         28/25        10.8      .190
MP4 1080p60 28M        183         26/25.2      10.9      .202

Dan.