Index: docs/mythtv-HOWTO.sgml =================================================================== --- docs/mythtv-HOWTO.sgml (revision 9044) +++ docs/mythtv-HOWTO.sgml (working copy) @@ -6334,57 +6334,182 @@ content even if the slave backend that recorded a program is not available. What is this transcoder thing, and how do I use it? -

The transcoder re-encodes files from one MythTV format to another. The -main purpose of the transcoder is to allow users with hardware -encoders (PVR-250) or systems that can only record in RTjpeg due to -performance reasons (multiple capture cards, slow system, etc) to create -MPEG-4 streams to save space. +

MythTV's built-in transcoder re-encodes recordings from one +codec/format to another. Transcoding is most commonly used to allow +users with hardware encoders (PVR cards, DVB cards, ATSC HD, etc.) or +systems that can only record in RTjpeg due to performance reasons +(multiple capture cards, slow system, etc) to create MPEG4 streams to +save space. However, with the addition of HD sources transcoding has +come to be used to transcode and resize HD MPEG2 recordings into +MPEG4 files to be played on systems too slow to deal with the original +HD recordings. There are even more uses for transcoding though, +including the ability to fix up MPEG2 recordings or remove commercials +without transcoding at all.

+

When MythTV transcodes a file to MPEG4 or RTjpeg the file format is +actually NuppelVideo (nuv.) You may have difficulty playing these +files back in other video players. If you want something more +portable you can look at some of the other sections in this HOWTO. -The transcoder can be used in two ways: +

The original file is actually removed when the transcoding process +is complete. Unless you're sure that you will be satisfied with the +result you may want to enable the mythv-setup option which causes +mythbackend to keep the original after transcoding. This option is on +the second page of the General section in mythtv-setup. Enabling this +allows you to compare the two files and restore the original if you +like. Outside of the initial setup phase it usually isn't necessary +to leave this option enabled. +

+ +

A recording can be transcoded in two ways: -Automatically re-encode every file once it has completed recording - After marking commercials, the transcoder can be run manually to -delete the commercials from the file (thus further saving space) +Automatically transcode the file once it has completed +recording. +Manually choosing to transcode a recording, usually after +importing a cutlist or manually marking commercials to be +removed. -The two methods are independent. The first is an automatic process that can be -enabled/disabled through the setup program; the second is a manual method which -must be invoked on each recording individually. -The second method can be used on files that have already been transcoded (or -files which were are already in the correct format), so only the frames -immediately following a cut section will be re-encoded, resulting in a very -minimal loss of quality. +

The second method can be used on files that have already been +transcoded (or files which were are already in the desired format), so +only the frames immediately following a cut section will be +re-encoded, resulting in a very minimal loss of quality when removing +commercials.

-To enable automatic transcoding, do the following: - start the setup program - under the host-specific settings: - set the Transcoder Auto-run checkbox +

The current transcoding system has a lot flexibility, but there are +a number of steps involved in setting it up. In order to +automatically transcode a given recording you must do the following: + +Configure recording profile for your capture source and enable +transcoding on one or more profiles. +Configure one or more transcoding profiles. +Create or alter existing scheduled recordings to enable +transcoding for that recording. + -For either manual or automatic transcoding: - start mythbackend - start mythfrontend - select setup, and the Transcoding recording profile. - now select either RTjpeg or MPEG-4 (selecting any of the hardware - encoders will result in the transcoder not working). - set the other parameters as you'd like. For best performance, you - should match the audio to the 'Default' profile. If you plan to - only use the manual transcoder, you can choose to set the video to - be the same as the default profile too (as long as it is MPEG-4 or - RTjpeg) +Configuring Recording Profiles to Allow Transcoding -Everything should now be setup properly. If you elected to use the -Auto-Run feature, the transcoder will automatically launch after each -recording is complete. The transcoder thread runs at a low priority, so it -should not impact any critical tasks or other recordings. +

Enter the Utilities/Setup,Setup,TV Settings,Recording Profiles +section in mythfrontend. Choose the option that corresponds with your +capture source (ignore the Transcoders for now.) Choose the quality +profile you are interested in enabling auto-transcode for. Make sure +"Enable auto-transcode after recording" is checked. This option might +ought to be called "allow auto-transcode" as we'll soon see though. +You might want to verify that the other settings for this profile are +correct while your here.

-If you want to manually transcode a program, simply press 'X' while -watching a recording (you should have already finished marking all -commercials). If you change your mind, hitting 'X' again will stop the -transcoding. +Configure Transcoding Profiles -Once the transcode is complete, mythbackend will replace the old file -with the new as soon as it is no longer in use. +

Enter the Transcoders section under Recording Profiles. There are +three quality settings to choose from and a two special Autodetect +settings. Later, when scheduling recordings you'll have to choose one +of Autodetect, High, Medium, and Low Quality transcode settings in +addition to the recording profile we set up above. If you choose the +Autodetect transcoding profile for a recording, MythTV will use the +"Autodetect from RTjpeg/MPEG4" profile for recordings which are +RTjpeg/MPEG4 files. Otherwise, it will use the "Autodetect from +MPEG2" provided it's an MPEG2 recording. If you choose one of the +others (High, Medium, Low) it will use the settings in that profile +regardless of the codec of the original recording.

+

There are a myriad of options for transcoding but the simplest +setting is to enable lossless transcoding (the first option) as this +removes all other options. Enabling lossless encoding simply removes +commercials (if you've marked them) and attempts to clean up MPEG2 +streams. Note: with this option MythTV will not apply denoise filters +or anything of the sort. It only attempts to massage the stream into +something cleaner and less likely to have trouble with other less +forgiving MPEG2 hardware/software (including players, video editors, +etc.)

+ +

If you enable resizing of the recording the next page has the +settings for choosing the final resolution. Note: MythTV will scale +the video as appropriate not crop it to this resolution.

+ +

The final two pages allow configuration of the video and audio +codecs. Although RTjpeg is an option for video codec I can think of +no reason you'd want to transcode to that format. It produces larger +files than MPEG4 and the recording will take more CPU +power to play back. The MPEG4 settings are not exactly +self-explanatory but you can judge for yourself the effects on the +final file and it's easy to experiment with until you achieve a good +compromise between size and quality. +

For those who've messed up their MPEG4 transcoding profile, the +defaults from memory are Bitrate: 2200-2500, MaxQ: 2, MinQ: 15, +MaxQDiff: 3, and "Scale bitrate for frame size" is enabled. The other +options are unchecked. If you're getting weird results from MPEG4 +transcoding try setting as above and go from there. + +Create/Alter Scheduled Recordings to Enable Transcoding + +

Transcoding is actually enabled on a per-recording basis. Two +things must be true before any given recording will be +auto-transcoded, however. The first is that the recording must have +been made with a recording profile that has auto-transcode enabled. +Under "Storage Options" for the recording you must set the "Record +using the "X" profile" to the profile you configured in the first +step. In addition, under the "Post Recording Options" section of the +recording you must also set "Transcode new recordings." This is also +where you specify the Transcoding profile to use (Auto, High, Medium, +Low.)

+ +

It may not be obvious from above but the flexibility of this system +is primarily to make it possible to auto-transcode a show recorded via +one source (ie: pcHDTV 3000), and not transcode that same show if it's +recorded on another kind of card (ie: PVR-250.) There are other uses +however. You could have a PVR-250 and a V4L card. You may want to +transcode the MPEG2 from the PVR-250 but there is no need to transcode +the recordings made with the V4L card, as it's already likely to be +MPEG4.

+ +

As an example, you could configure the Default profile for +"Hardware DVB Encoders" (the profile group used for DVB cards, +including the ATSC HD type cards like pcHDTV 3000) to "Enable +auto-transcoding." In the Default profile for MPEG2 Encoders (PVR +cards) you'd leave "Enable auto-transcoding" unchecked. For programs +that are available on both kinds of cards (think Law & Order, which is +available on virtually every channel) you'd set the recording profile +to Default and enable auto-transcoding in the record settings. Then +you pick your transcoding profile. When Law & Order plays on your DVB +card, it will get transcoded. When it plays on a channel available +via your PVR card, it won't be.

+ +Manual Transcoding +

Manually transcoding a recording is also possible. It can be +activated while watching a show by hitting 'x', or from the OSD menus +by choosing the Transcode option, or by choosing Job Options/Transcode +from the info menu accessed from the Watch or Delete Recordings +screens. +

The transcoding profile used for manual transcoding is whatever you +set when you originally configured this recording, even if you didn't +enable auto-transcoding. The only way to change what transcoding +profile will be used is to alter the transcoder column in the recorded +table in the database. The transcoder column contains a number which +corresponds with the id column in the recordingprofiles table. You +can find out the id number for each profile in the transcoder group +with an SQL command like: + + +mysql> select r.* from recordingprofiles r,profilegroups p where p.name='Transcoders' and p.id=r.profilegroup; ++----+----------------+------------+------------+--------------+ +| id | name | videocodec | audiocodec | profilegroup | ++----+----------------+------------+------------+--------------+ +| 21 | RTjpeg/MPEG4 | MPEG-4 | MP3 | 6 | +| 22 | MPEG2 | MPEG-4 | MP3 | 6 | +| 27 | High Quality | MPEG-4 | MP3 | 6 | +| 28 | Medium Quality | MPEG-4 | MP3 | 6 | +| 29 | Low Quality | MPEG-4 | MP3 | 6 | ++----+----------------+------------+------------+--------------+ +5 rows in set (0.01 sec) + +mysql> + + +

Armed with the knowledge of what the profile ID's are you can also +choose to run mythtranscode from the command line explicitly +specifying the transcoder profile. Run mythtranscode with --help for +usage information. + + Changing your hostname

If you need to change the name of the computers used with MythTV you'll