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Logfile Playback

CANtrace supports the playback of existing log files in the Vector ASCII (ASC) and Vector Binary Log Formats (BLF). CANtrace supports any compatible file, whether generated by CANtrace, a hardware CAN logger, or a third-party tool. If a log file is not in a supported format, an error message will be displayed.

Quick guide

  1. Select your logfile by clicking browse (format: .asc, .blf, or .txt).
  2. Activate the channel.
  3. Click Close and Go on bus.

Figure: Play Log File Settings

Playback Channel Modes

Playback can be configured in one of three ways:

1. Determined by the Log File (Normal Internal Playback)

  • Function: Used for normal internal playback, displaying messages in the Trace, Data, and Graph tabs as if they were coming from a real CAN bus.
  • Behavior: Messages retain their original channel numbers as recorded in the log file.
  • Network Impact: No real CAN messages are received or transmitted from the physical CAN network.
  • Timing: Playback starts when going "on bus" and continues until the log file reaches its end, at which point CANtrace automatically goes off bus. With Loop Playback on, playback starts again from the beginning instead.

2. Channel 0 (Display Only)

  • Function: Used for internal playback, similar to "Determined by the Log File."
  • Behavior: Regardless of the original channel recorded, all messages appear as originating from software channel 0.
  • Network Impact: Live CAN messages can still be received or transmitted from the network on other channels.
  • Timing: Playback starts when going "on bus" and stops at the end of the file, unless Loop Playback is on.

3. Channel 1 to 9 (Physical CAN Bus)

  • Function: Messages from the log file are transmitted to a configured physical CAN channel.
  • Behavior: All messages, regardless of their original channel, are sent to the selected physical CAN bus.
  • Timing: CANtrace remains "on bus" after playback is complete.

Timing Accuracy

When sending messages to the physical CAN bus, timing accuracy is limited by Windows timers. Because Windows is not a real-time operating system, a message may occasionally be sent up to 100ms later than indicated by the timestamp. Messages are always sent in the correct order.

Configuration Options

Channel Active

  • This setting is disabled until a log file is specified.
  • Ticking this box activates log file playback.
  • Unless a physical CAN channel is selected, you will be prompted to deactivate all other channels to prevent mixing live data with log data.

Playback Channel Selector

  • This drop-down menu allows you to select the software channel for playback.
  • If the channel amount selector is set to a value greater than 1, physical options (e.g., "1 - CAN bus") will appear.
  • Important: A CAN interface hardware channel must be assigned to the selected software channel for physical playback to function.

Log File Path

  • Click Browse to select a file. The dialog defaults to compatible extensions (ASC, BLF, and TXT).
  • The first message in the log file is played back immediately upon going "on bus," regardless of its timestamp.

Log Playback Rate

There are two playback rate options:

  • Maximum Rate: Plays back messages at maximum speed. Ideal for quickly processing lengthy logs to generate graphs.
  • Recorded Rate: Plays back messages at the same speed they were recorded, ensuring real-time replication.

Playback Options

  • Loop Playback: When the end of the log file is reached, playback starts again from the beginning and continues until you go off bus.
    • Loop Playback is only available with the Recorded Rate. Selecting Maximum Rate clears and disables the option.
    • Timestamps keep increasing from one loop to the next, so the Trace and Graph tabs show one continuous timeline instead of jumping back to the start of the log.
    • With Loop Playback on, CANtrace does not go off bus at the end of the file, whatever the playback channel.
    • The setting is saved in the project file.

Playback Status

The status bar shows the state of the log file playback when channel 0 (Log File Playback) is active:

  • Progress bar and percentage: The bar and Playback: xx % show how much of the log file has been played. Every percent fills one more step of the bar.
  • Repeat icon: Shown next to the percentage when Loop Playback is on. The bar and percentage are then for the current loop and start again from 0 % on every loop.
  • Details: Hover the mouse over the playback status to see the log file name, the played time and the full length of the log file, for example Playing 1:23 / 5:00 | mylog.blf. The first word tells the state: Ready, Playing, Stopped or Finished. Logs of an hour or longer are shown as hours:minutes:seconds.

After going off bus, the status bar keeps showing how far the latest playback got and whether Loop Playback is on. The hover then tells whether the playback was stopped or played to the end. Before the first playback, the status bar shows 0 % and the hover shows the length of the log file. When another log file is selected, the status starts again from 0 %.

When log file playback is not in use, the status bar shows Playback: N/A.

When the log file is played to a CAN bus channel and that channel goes error passive or bus off, the percentage turns brown (error passive) or red (bus off) and the hover shows for example Channel 3 error passive. The playback continues, but its messages may not reach the bus, for example when no other node on the bus acknowledges them.

The progress is based on the timestamps in the log file, not on the number of messages. CANtrace reads the first and last timestamp from the beginning and the end of the log file, so this is quick also for large files. If the length of the log file cannot be found, for example because the file is damaged, the status bar shows -- % and the full length is shown as --:--. Time spent paused is not counted as played time.