Cablecast Supported File Formats

Applies To

• Cablecast Video servers

Overview

Cablecast video servers can play back many different combinations of file formats, video codecs, and audio codecs. To work with the video server, files must meet certain requirements. This article lists those requirements so you can prepare files that are compatible with Cablecast servers.

The article is organized into sections. The first covers basic broadcast information that applies to all file formats, including video resolutions and audio settings. Later sections cover each supported file format, then list requirements for specific codecs.

This article covers playback only.

"File format" and "file wrapper" mean the same thing throughout this article.

Recommended Encoding Settings

Use the settings below when encoding files for upload to Cablecast. These settings give you the best chance of compatibility.

HD/MP4

Video Encoder

Broadcast Video Resolutions

Broadcast video resolutions are made up of the following elements:

• Width: number of pixels per line

• Height: number of lines

• Aspect Ratio: the shape of each pixel

• Frame Rate: the number of frames shown per second

• Scan Mode: the order in which each picture (field or frame) is displayed

Every file played by the video server must match one of the supported resolutions below. This is the first step to making a file compatible. For example, if a file contains SD content and the server is in the US, its video settings should match the NTSC resolution below.

Note: Interlaced video is sometimes measured in samples per second instead of frames per second. For example, 29.97 frames per second equals 59.94 samples per second, where each sample is one video field. This article always uses frames per second. Cablecast video servers also work in frames per second.

NTSC

[Note 2] Compressed video spans 480 lines; uncompressed video usually spans 486 lines.
[Note 3] Progressive scan content is supported.

PAL

[Note 2a] Compressed video spans the listed lines; uncompressed video may span more.
[Note 3a] Progressive scan content is supported.

720p

1080i

[Note 4] Some encoders support a width of 1440 (MPEG-2, H.264/AVC).
[Note 5] Progressive scan content is supported, but is not to be confused with 1080p below.

1080p

Audio Specification

Audio specification is not affected by video resolution.

[Note 6] With the exception of MPEG files, where 44,100 samples per second (44.1 kHz) is also supported.

File Formats

The following sections cover each supported file format and how its content must be set up to work with Cablecast video servers.

Each table shows the supported combinations of video and audio content for that file format.

MOV / MP4

MOV [Note 7] and MP4 files are treated the same way in Cablecast video servers.

[Note 7] Playback does not rely on QuickTime.

PCM Audio Restrictions

PCM audio supports 2 to 16 channels at 16-bit or 24-bit (24-bit in a 32-bit container), at 48 kHz. Audio can be stored as stereo pairs, mono tracks, or one multiplexed (muxed) track. All tracks in the file must use the same format — all mono, all stereo, or all muxed. Both big endian and little endian are supported; little endian is preferred.

Cablecast plays out the first two audio channels only.

AAC Audio Restrictions

AAC audio must use the Low Complexity (LC) profile at 48 kHz with 2, 4, or 8 channels. AAC audio is only supported with H.264/AVC video.

Cablecast plays out the first two audio channels only.

Closed Captioning and AFD

Closed captions and AFD (Active Format Description) are only supported when the video codec is H.264/AVC. The caption or AFD data must be stored using one of these standards: AVCHD, AVC-Intra, ANSI/SCTE 128, or ETSI EN 301 775.

For AVCHD and AVC-Intra, store the data as unregistered SEI (Supplemental Enhancement Information) messages in the H.264/AVC stream. For ANSI/SCTE 128 and ETSI EN 301 775, store the data as registered SEI messages in the H.264/AVC stream.

Note on AFD: If no AFD is decoded from the content file, Cablecast injects the appropriate AFD code into the playback's ancillary data stream.

MPEG

Video with multiplexed audio in a program stream or transport stream, saved as an .mpg, .mpeg, or .m2v file.

Audio Restrictions

MPEG audio must be combined (multiplexed) with the video at 44.1 kHz or 48 kHz, at 16 bits per sample.

The audio stream can contain 1, 2, 4, or 8 pairs of stereo audio tracks (2, 4, 8, or 16 total channels).

Closed Captioning and AFD

Closed captions and AFD should be stored in the user data (metadata) of the MPEG-2 file. That data must follow the ATSC A/53 standard.

Note on AFD: If no AFD is decoded from the content file, Cablecast injects the appropriate AFD code into the playback's ancillary data stream.

AVI

Codecs

The following sections describe how compressed content must be set up to work with Cablecast video servers. These requirements apply regardless of the file format used.

Video Codecs

H.264/AVC

• Profile: Main, High, High 10, High 4:2:2

• SD Level: 2.2, 3, 3.1

• HD Level: 3.2, 4, 4.1, 4.2, 5, 5.1, 5.2

• AVC-Intra class 50

• AVC-Intra class 100

• Entropy: CABAC, CAVLC

• Max GOP size (N): 30 [Note 8]

• Frame rate mode must be constant

• Color primaries: BT 601, BT 709

[Note 8] Longer GOP sizes will play but may result in non-real-time playback, especially around cut points inside sequences or when resuming playback.

Tip: H.264/AVC files with a fast start header (also called a "moov atom" at the start of the file) are recommended if you plan to use the Trim File feature in Show Records. See Trimming Files in Cablecast for details.

MPEG

• Main profile @ Main level (4:2:0)

• Main profile @ High level (4:2:0)

• Main profile @ High level-1440 (4:2:0)

• 422 profile @ Main level

• 422 profile @ High level

DNxHD

• 36, 145, 220, 220x

ProRes

• ProRes 422

• ProRes 422 HQ

• ProRes 422 LT

• ProRes 422 Proxy

Audio Codecs

PCM

• 48 kHz with 2, 4, 8, 16, or 32 audio channels [Note 9] at 24-bit (24-bit in a 32-bit payload) [Note 10]

• 48 kHz with 2 audio channels [Note 9] at 16-bit

[Note 9] Cablecast video servers play the first 2 audio channels only.
[Note 10] 24-bit audio is stored inside a 32-bit container using the most significant bits (8–31). Some applications may identify the audio as 32-bit.

AAC

Low Complexity profile at 48 kHz with 1, 4, or 8 channels [Note 9].

Troubleshooting

Active Lines

The active lines information below can help you diagnose files that play with jerky motion or excessive aliasing, especially in NTSC. Following these specs helps prevent field inversion and temporal inversion artifacts, which are most common in MPEG-2 480i NTSC footage.

Note: These are quality guidelines. Not following them will not affect other parts of playback.

NTSC Active Lines

Uncompressed NTSC video uses Bottom Field First (BFF) field order. However, MPEG, H.264/AVC, and ProRes video should be stored with Top Field First (TFF) field order. This difference exists because compressed NTSC video is 480 lines tall, while uncompressed NTSC video is 486 lines tall.

During compression, 5 lines are removed from the top of the frame and 1 line from the bottom — 6 lines total. Because an odd number of lines is removed from the top, the field order of the remaining content shifts to Top Field First.

When the decoder reads the file and detects Top Field First, it places the decoded 480 lines starting at line 5 and plays back the full 486-line frame using Bottom Field First — reversing the original compression process.

If the field order is tagged incorrectly in the file, the decoded content will be placed in the wrong position, causing field inversion artifacts.

PAL Active Lines

720p Active Lines

1080i Active Lines

1080p Active Lines