fix: ignore buffered content less than 1e-4s (shaka-project#6802)

On Firefox, in some cases after a period ends, seeking shortly after
will cause playback to fail or stall.
This occurs when the next period has small gaps and we're seeking to
after the gap. Seeking to before the gap succeeds. Even though the seek
requests the soure buffers to be fully cleared, Firefox actually keeps
around less than 1e-4s of content and won't let us forcibly remove this
content. Trying to call flush causes in infinite loop.
This leftover content makes shaka think that the buffer end in where we
used to be even though the presentation time reflects where we seeked
to. This means that playback doesn't continue. The buffer contitues
getting filled and playback will either fail when the SourcBuffer is
filled and triggers a QuotaExceededError or contiue when the buffer will
reach the presentationTime.

lib/media/time_ranges_utils.js

@@ -11,6 +11,19 @@ goog.provide('shaka.media.TimeRangesUtils');
  * @summary A set of utility functions for dealing with TimeRanges objects.
  */
 shaka.media.TimeRangesUtils = class {
+  /**
+   * Returns whether the buffer is small enough to be ignored.
+   *
+   * @param {TimeRanges} b
+   * @return {boolean}
+   * @private
+   */
+  static isBufferNegligible_(b) {
+    // Workaround Safari bug: https://bit.ly/2trx6O8
+    // Firefox may leave <1e-4s of data in buffer after clearing all content
+    return b.length == 1 && b.end(0) - b.start(0) < 1e-4;
+  }
+
   /**
    * Gets the first timestamp in the buffer.
    *
@@ -22,8 +35,7 @@ shaka.media.TimeRangesUtils = class {
     if (!b) {
       return null;
     }
-    // Workaround Safari bug: https://bit.ly/2trx6O8
-    if (b.length == 1 && b.end(0) - b.start(0) < 1e-6) {
+    if (shaka.media.TimeRangesUtils.isBufferNegligible_(b)) {
       return null;
     }
     // Workaround Edge bug: https://bit.ly/2JYLPeB
@@ -45,8 +57,7 @@ shaka.media.TimeRangesUtils = class {
     if (!b) {
       return null;
     }
-    // Workaround Safari bug: https://bit.ly/2trx6O8
-    if (b.length == 1 && b.end(0) - b.start(0) < 1e-6) {
+    if (shaka.media.TimeRangesUtils.isBufferNegligible_(b)) {
       return null;
     }
     return b.length ? b.end(b.length - 1) : null;
@@ -64,8 +75,7 @@ shaka.media.TimeRangesUtils = class {
     if (!b || !b.length) {
       return false;
     }
-    // Workaround Safari bug: https://bit.ly/2trx6O8
-    if (b.length == 1 && b.end(0) - b.start(0) < 1e-6) {
+    if (shaka.media.TimeRangesUtils.isBufferNegligible_(b)) {
       return false;
     }
 
@@ -92,8 +102,7 @@ shaka.media.TimeRangesUtils = class {
     if (!b || !b.length) {
       return 0;
     }
-    // Workaround Safari bug: https://bit.ly/2trx6O8
-    if (b.length == 1 && b.end(0) - b.start(0) < 1e-6) {
+    if (shaka.media.TimeRangesUtils.isBufferNegligible_(b)) {
       return 0;
     }
 
@@ -128,8 +137,7 @@ shaka.media.TimeRangesUtils = class {
     if (!b || !b.length) {
       return null;
     }
-    // Workaround Safari bug: https://bit.ly/2trx6O8
-    if (b.length == 1 && b.end(0) - b.start(0) < 1e-6) {
+    if (shaka.media.TimeRangesUtils.isBufferNegligible_(b)) {
       return null;
     }