About this guide
This guide explains the most common warning and error messages in an Alta Channel Log: what each one means, what triggers it, and where to look first.
To find a message, search this page for a fixed part of the text, such as PCR Discontinuity or Input gap of. Don't search for numbers, because they change every time the message appears.
Message wording can vary slightly between Alta releases. If a message isn't listed here, contact AI-Media support with the log lines around it.
Reading a log line
Each Alta channel writes its own log. Logs roll over daily at midnight and when they reach a size limit. The same lines appear live in the Alta UI.
Each line shows a timestamp, a severity and the message:
2026-10-27 14:03:11: <warning> fblib: PCR Discontinuity detected: ...
Prefixes tell you which part of Alta wrote the line:
| Prefix | Component |
| fblib: | MPEG-TS processing (2022 / SRT / UDP channels only) |
| iCap: | Caption connection to iCap / LEXI |
| SCTE104: | SCTE-104 ad-insertion signalling (2110 channels) |
| FFmpeg Driver: | Audio processing, including LEXI Voice |
| Telnet: | Telnet caption input or output |
| No prefix | The Alta channel itself |
Severity levels:
- warning – something unusual was detected and Alta handled it automatically.
- error – an operation failed or data was dropped. Check what happened around it.
- fatal – usually at startup, from invalid settings or a missing licence. The channel stops or won't start.
Throttled lines. Alta writes at most 200 lines per second. Above that, it writes one summary line instead: Log messages have exceeded maximum threshold... Messages throttled count: N. The lines just before it show the cause, and the log around that moment is incomplete.
Input timing (PCR)
PCR (Program Clock Reference) is the timing signal inside an MPEG-TS input. Alta times its output from it, so problems with the incoming PCR appear here. The cause is almost always upstream: a source switch, a router cut, an upstream encoder restart, a splice between unrelated sources, or a corrupted input.
| Message | Triggered when | Severity |
| PCR Discontinuity detected | The input clock jumped backwards, or jumped forwards by more than 0.5 s (fixed CBR output rate) or 4 s (automatic rate). Alta re-syncs its output clock; large jumps reset processing. | warning |
| PCR's not following in continuous domain | Successive clock values don't agree on a single timeline. The input clock is erratic. | warning |
| PCR's difference of N (< 0 or > 0.2s) so push everything to output as is | Low Latency CBR mode only. Clock values are more than 0.2 s apart (the standard requires one at least every 0.1 s), so Alta sends data out without pacing. | warning |
| No PCR in low latency CBR buf for 0.2s... / No PCR at the start of low latency CBR buf... / Back to back PCR's | Low Latency CBR mode only. The input has too few, or irregular, clock values. | warning |
These informational lines are normal and need no action: PCR Wraparound detected (the clock's regular 26.5-hour rollover), putting PCR on probation, dropped single PCR sample and accepting new PCR domain.
Input stream integrity
These messages mean the MPEG-TS input was damaged or incomplete before it reached Alta. Check the source and the network path to Alta.
| Message | Triggered when | Severity |
| realtime ts out of sync, skipping to next sync byte | A packet didn't start where expected. Logged up to 10 times, then suppressed until the stream recovers; Suppressed N ts sync errors gives the total. | error |
| continuity count error on PID=XXXX exp A but got B | Packets on that stream were lost or arrived out of order. Same 10-then-suppress rule, per stream. | error |
| PAT / PMT error | The stream's program tables are missing, or arrive more than 0.5 s apart. | error |
| transport stream errors being indicated | An upstream device has already flagged packets as corrupt. | warning |
Output rate and buffering
These messages mean Alta's buffers are filling faster than the output can drain them. The usual fix is a configuration change, most often raising the CBR transport rate.
| Message | Triggered when | Severity |
| Input TS rate (N bps) exceeds CBR output TS rate (M bps) by more than 0.25% | The input bitrate is higher than the configured CBR output rate. Raise the CBR transport rate in channel settings. | error |
| Output buffer is filling up! N% full... | The output buffer is more than 75% full. Output is draining slower than input arrives. | warning |
| not enough buffer space for a new GOP... followed by Clearing GOP buffer to avoid backups, some data may be lost | The output buffer can't hold the next group of pictures, so it is cleared. Some output is lost. | warning |
| Input mux buffer full - could not commit complete input data..., clearing buffer | The input buffer is full and incoming data is dropped. | error |
| buffer delay < 0 ... temporarily disabling PES smoothing | A stream has fallen behind the output clock. | warning |
| EMERGENCY OVERRIDE: Forcing selection of extremely late packet... | A packet is more than 10 s late and is forced out. | warning |
| ts_out overflowed | An output chunk filled up during processing. | error |
| [MUX_DRIFT] ..., [MUX_STALL] ..., [TSTD_OVERFLOW] ... | Internal timing diagnostics. Include these lines when contacting support. | warning / error |
Licensing
At startup, Alta looks for an offline licence first, then tries cloud licensing. Each running channel uses one licence.
| Message | Triggered when | Severity |
| Unable to get offline license | No valid, unused offline licence file was found. Normal on cloud-licensed systems; Alta moves on to cloud licensing. | warning |
| Cloud license error on initial check: <reason> | Cloud licensing also failed. The reason will be one of: invalid key, no licences exist, no licences available, licence expired, network error, or licence server error. This is the line that matters. | error |
| Cloud license error on initialize: ... | The cloud licensing service could not start. | warning |
| Container startup refused: no license key provided | A containerised deployment started without a licence key. | warning |
| Unable to get any valid license | No offline or cloud licence was available. The channel won't start. | fatal |
| Entering license renewal grace period, you have D days, H hours... | A licence renewal failed. The channel keeps running for the grace period shown. | warning |
| You have D days... to renew your license... | Reminder during the grace period. | warning |
| License failure grace period has ended / Terminating due to licensing failure... | The grace period expired and the channel stops. | error / fatal |
If you see licensing errors, check that the licence key is correct and that the Alta system can reach the licence server.
Network input and output (RTP / UDP / SRT)
These messages cover receiving the video stream into Alta and sending it back out.
| Message | Triggered when | Severity |
| video channel: Input gap of N ms | No input packets arrived for more than 1 second. | warning |
| No output coming from parser for extended period - resetting | Input is arriving, but nothing usable has come out of it for about 10 seconds' worth of data. Alta resets input processing. | warning |
| Input FIFO full, resetting parser | Input is arriving faster than Alta can process it. | warning |
| UDP packet payload size not a multiple of TS packet length (188 or 204) | The input isn't whole TS packets. Usually Alta is set to UDP while the sender uses RTP, or the reverse. | error |
| Dropping SRT message with non-188-byte-aligned size | The SRT input isn't whole TS packets. Logged at most every 5 s. | error |
| epoll returning persistent errors... SRT receive is broken, not merely idle | 100 SRT receive errors in a row. Logged at most every 30 s. | error |
| SRT transmitter dropping packets, there is no connected receiver | Nothing is connected to the SRT output, so output packets are discarded. | warning |
| SRT ... could not apply encryption, refusing ... | The SRT passphrase or key length was rejected. Alta won't fall back to an unencrypted connection. Check the passphrase settings at both ends. | error |
| Could not join specified multicast group... / Failed to bind UDP socket on port N | Alta couldn't open the configured input address or port. Check network settings and that the port isn't already in use. | error |
| Send buffer runout. Target rate: N | Alta ran out of data to send at the target output rate. | warning |
| Must wait to fill buffer before beginning to write again... | Follows a runout. Consider increasing the UDP buffer size in channel settings. | warning |
| Packet send pacer reporting elapsed time of N ms between emitted packets... | More than 100 ms passed between output packets. Usually high CPU load on the host or UDP buffer limits. | warning |
| UDP receive buffer limited by OS settings to N bytes | The operating system capped the receive buffer below what Alta requested. On Linux, raise net.core.rmem_max. | warning |
LEXI Voice and audio processing
These lines start with FFmpeg Driver: and cover audio handling, including LEXI Voice dubbing.
| Message | Triggered when | Severity |
| AAC buffer is full: Skipping processing of dub data until condition clears | The dubbed-audio output buffer is more than 90% full. | warning |
| Buffer buildup detected: Leaking down buffer from remote source... | More than 3 seconds of dubbed audio is queued. Alta trims the queue; audio may sound distorted briefly. | warning |
| Major Buffer buildup detected: disabling audio contribution data... | More than 5 seconds of dubbed audio is queued. Dubbed audio is paused until it clears. | warning |
| Resetting due to change in input stream parameters | The input's video or audio format changed mid-stream (for example, the number of audio channels). Audio processing restarts. | warning |
| Falling behind with more than N bytes in the input buffer... | More than 500 MB of input is waiting for audio processing. The buffer is cleared. | warning |
| Cannot find a video stream with ID ... | The configured video stream wasn't found in the input. | warning |
| Hit EOF / Resetting after EOF | The input ended or was interrupted. Processing restarts when input returns. | warning |
SMPTE 2110
These messages appear on SMPTE 2110 channels only.
| Message | Triggered when | Severity |
| RTP receive - no packets from source for 5 seconds - Waiting for packets | No 2110 packets arrived for more than 5 seconds. | warning |
| RTP packets on input outside of sync tolerance... | A packet's timestamp is outside the expected range. The first 10 are logged, then every 50,000th. | warning |
| Too many out-of-sync packets (N), forcing timestamp resynchronization | More than 100 out-of-sync packets. Alta re-syncs to the input. | warning |
| Rx anc packet not received in time for frame period... | The ancillary (caption) data for a frame arrived late. The first 50 are logged. | warning |
| ptpd resync detected (drift=N samples...) | The PTP clock stepped and the audio output drifted from it. Alta re-aligns. Logged at most once per second. Check PTP stability on the network. | warning |
| Audio queue overflow (N packets), clearing... | More than 1,000 audio packets were waiting. The queue is cleared. | warning |
| SDP: ... / Did not find 2110-xx ... m section in SDP | The SDP (from a file or NMOS) is malformed or is missing the expected stream. | error |
| Receive buffer size limited by OS settings... | The operating system capped the receive buffer below what Alta requested. | warning |
Alerts shown in the Alta UI
Some conditions also raise a named alert counter in the Alta UI. Each alert usually has a matching log line nearby.
| UI alert | Raised when |
| PCR Discontinuity | The input clock jumped (see Input timing). |
| TS Sync Loss | Packets didn't start where expected. |
| Continuity Count Error | Packets on a stream were lost or reordered. |
| Transport Error | An upstream device flagged a packet as corrupt. |
| PAT Error / PMT Error | Program tables are missing or more than 0.5 s apart. |
| PID Error | An expected video, audio or data stream stopped arriving. |
| Video Missing | No video for 1 second or longer. |
| RTP packets lost | Gaps in the RTP packet sequence. |
| RTP packets out of order | RTP packets arrived in the wrong order. |
| RTP packets recovered via FEC | Lost packets were rebuilt using forward error correction. |
| RTP Parse Errors | An RTP packet couldn't be read. |
| RTP Sequence Number Rebase | The RTP packet counter was reset. |
| New SSRC count | The sender's stream identifier changed, usually a source switch or sender restart. |
| Output underflow gaps | Alta ran out of data to send at the target rate. |
| Output jitter gaps | More than 30 ms passed between output packets. |
Startup and configuration errors
Most fatal lines appear at startup and mean a channel setting is missing or invalid. The message names the setting, for example Missing option ..., Invalid ... or Unsupported .... Correct the channel configuration and restart the channel.
Other common startup and connection messages:
| Message | Meaning | Severity |
| Requested media interface address ... not currently accessible | The network interface set for the channel isn't available on this system. | fatal |
| Could not open RTP/UDP primary stream, terminating | Alta couldn't open the configured input. | fatal |
| Could not create output SRT transmitter / Could not create output video session | Alta couldn't open the configured output. | fatal |
| iCap Driver: Connection error: ... | The caption connection to iCap / LEXI failed. Alta retries automatically. | error |
| Logged out of iCap... | The iCap session ended. If it keeps happening, the login may be in use on another device. | warning |
| Not starting iCap networking, no company credential provided | No iCap company is set for the channel. | warning |
| <signal> - closing | The channel was stopped or restarted. | fatal |
| Container environment detected: redis log publishing disabled | Containerised deployments only. Logs are written to file but not shown live in the UI. | warning |